CHESS.

ANSWERS TO CORRESPONDENTS.

All communications should be addressed to the EDITOR
ALL Communications for this department must be of the ENGLISH MECHANIC, 31, Tavistock-street, Covent
addressed Chess Editor, 22, Chancery-lane, W.C.
Garden, W.C.

NOTICES TO CORRESPONDESTA. CORRECT SOLUTIONS to 701 by J. W. Jubb, W. W., and 8. L.; to 70 by S. L.; to 6 and 700 by W. W. Arsos-Problem 696 is a two-mover, and not a threemover. Please re-examine.

J. W. Juze.-Have writen you.

CRESS ITEMS.

Os Saturday, October 8th last, was the occasion of a bezent given to the Guiding Spirit" of the well-known act/Laton Chess Player, Mephisto. There was a nume rous attendance, including a great number of celebrated Chess Players. Some of the games played were most intersxt ng, and, exepting in one in-tance, all resuited in favour of Mephisto The entertainment was a thorough success, proving the increased popularity of Chess.

Os Wednesday, October 12, last, Mr. Blackburne, the winner of the late Berlin Chess Congress, gave one of his marvellous blindfold fests at the City of London! Chess Club. He was opposed to eight strong opponents, and the result at the finish of the evening was Mr. Blackburne 5 games, one lost to Mr. Piper, one drawn to Mr. Stevens, and one adjourned with Mr Chappell. There was a crowded attendance all the evening; among the visitors were Mears. Steitz, Hoffer, MacDonnell, Collins, and Taylor. The following are the names of the antagonists of Mr. Blackburne: Messrs. Piper, Chappell, Stevens, Cutler, Gastineau, Watson, Humner, and Atkin

HINTS TO CORRESPONDENTS.

1. Write on one side of the paper only, and put drawIngs for illustrations on separate pieces of paper. 2. Put titles to queries, and when answering queries put the numbers as well as the titles of the queries to which the replies refer, 3. No charge is made for inserting letters, queries, or replies. 4. Letters or queries asking for addresses of manufacturers or correspondents, or where tools or other articles can be purchased, or replies giving such information, cannot be inserted except as advertisements. 5. No question asking for educational or scientific information is answered through the post. 6. Letters Bent to correspondents, under cover to the Editor, are not forwarded; and the names of correspondents are not given to inquirers.

...Attention is especially drawn to hint No. 4. The
space devoted to letters, queries, and replies is meant for
the general good, and it is not fair to occupy it with ques-
tions such as are indicated above, which are only of indi-
vidual interest, and which, if not advertisements in them-
selves, lead to replies which are. The "Sixpenny Sale
Column" offers a cheap means of obtaining such infor-
mation, and we trust our readers will avail themselves of it.
The following are the initials, &c., of letters to hand up
to Wednesday evening, Oct. 19, and unacknowledged
elsewhere:-

J. FRASER.-Venables and Co.--H. Milnes.-R. Mills.-
J. B. Battersby.-Earl Russell.-E. P. Alexander.-
Rev. N. S. Godfrey.-C. R. C. Hibbert.-Barnett, Son,
and Foster.-Selig Sonnenthal and Co.-D. Fraser.-J.
E. Nugent.-Cutler.-C. J. E.-M.M.I.Sc.8.-Walter.
-Ignoramus.-Youth-Angler.-Little Binks.-G. H.
Wilkinson.-B. H.-Hot Water.-F. C.-A Young Ob-
server.-R.-Birmingham.-J. J. H.-Nemo.-Poly-
mathy.-Tittesworth. - Mechanic.-W. Osbaldeston.-
Glass Bottle.-Land Lubber.-P. D.-Tarnash.-An
English Yeoman.-J. Stubbs.-W. R. Birt.-Guido.-
L. E. J.-N. W., Ealing. - Dunrod.-Prismatique.-C.
Taylor.-Dubliniensis.-Plate Cleaner.-Vulcanite.-
Lighter.-A. C. P.

plate is cleaned, and then with the card over is sub-
jected to the heavy pressure of a roller. The ink adheres
to the card)-C. S. B. (Culley's work is the most
complete, published by Longmans; but Bond's "Hand-
book of the Telegraph," Crosby Lockwood and C.,
Stationers' Hall-court, E.C., will suit you, as it is pre-
pared for candidates for the service, price 38. For the
other subject you can have nothing better than our back
volumes. There is no cheap and trustworthy book.)-
C. O. (Rather too vague and rambling.)-PUCK. (A
water-clock was illustrated on p. 502, Vol. XXIX. See
also Vol. XXXII., under heads Clepsydrae and sand-
clocks.)-No Go. (In No. 820, but it has been much
modified. 2. Shellac dissolves readily in methylated
spirit. For your purpose use a smaller quantity of
spirit, and apply heat.)- WroMA. (Merely to simplify
and render uniform. They are understood all over the
world now, without so much liability to error.)-B. 0.8.
(See p. 442, last volume, and the numbers since.)-
G. FRYER. (The two queries have been answered ma y
times. Baking powder is composed of tartaric acid,
bicarbonate of soda, and farina. German yeast is pre-
pared by squeezing out the moisture from the yeast
obtained in the German method of fermenting. There
are several imitations. We fail to find any information
in the reply about the orguinette, and cartridge-paper
is too rough.)-H. G. B. (No. 846. If you use a patent
for business purposes you are rendering yourself liable
to an action for damages; if merely for experiment the
damages are clearly so small that no patentee would
bring an action.)-JOHN DAVIES. (We illustrated the
Malden dissolver in No. 401.)-T. W. (Taking the
example given on Oct. 7, T means time of perihelion
passage, longitude of perihelion, longitude of
ascending node, i inclination, and log. 9 log. of peri-
helion distance.)-CARLISSIM. (The transit takes place
a little after ten at night on Nov. 7, and lasts about five
hours, but it is invisible here. 2. Quite possible to
make such a clock; but it would be an awful waste of
time.)-A. K. (Try soaking in melted paraffia, and for
transparencies generally see a discussion in Vol.
XXXI.)-F. L. S. (For the fossils, you should procure
some of the works published by the Palæontographical
Society, and Collins's books on Mineralogy will help
you with the minerals.)-RECULVERS. (All that is
known is that pilocarpin stimulates the growth of the
hair, but it is doubtful whether in this country any ex-
periments have been made with it.)-D. 8. H. (You
can make one with sheets of copper and zinc separated
by bletting paper damped with solution of sulphuri
acid, but it will not do you any good. Take exercise in
the fresh air.)-R. W. (Yes; if the meters are accu-
rate it will make no difference.)-WORKING TOX (If
you know the size they are, in the book, make your
drawings twice, three times, or four times as large. For
instance, if a foot is to be repsesented by half an inch,
you might make your drawings two inches to the foot.
Engravers easily reduce by 2, 3, or 4, but they don't like
1 or 2.)-RANDOLPH, POULTRY FARMER. (You want a
clock to drop a weight on a lever, and it would be pre-
ferable to use one of the lamps which are fitted with
extinguishing contrivances)-F. H. R. (Very probably
it might be used for excluding frost from a garden
frame if the glass was covered with mats. Full par
ticulars in the last two numbers, in which it is distinctly
stated that the action is due to the salt passing from
the solid to the liquid state and back again. The case
is heated to render the salt liquid, and it gives out heatss
it returns to the solid state)-MCSICAL. (You can
probably get a new set of reeds at any music-shop, but
an eight-keyed accordion is at best a toy.)-ETCHER
(Use white wax. The acid eat through pinholes in
your varnish.)-A. S. R. (The Sanders brake was
illustrated on pp. 315, 397, Nos. 689, 692. See the
indices of the last four volumes for more particulars.)
-BRONZE. (Refer to recent indices. The process
depends on the kind of metal.)-W. WATSON. (Nitrate
of silver.)-JUVENTUS. (See p. 295, No.766. It is done
by using varnish to cement the ink, and then rubbing
the paper away at the back; but perhaps you meal
drawings which are split and then mounted on paper.)
-T. MILLER. (Neither disease you mention is "real
cancer." The last you name is generally curable, the
first seldom so, but may be periodically relieved by a
not very severe operation. "Real cancer" is not cur-
able, except, of course, when it can be totally removed
from some accessible part by the knife.)-EXHIBITOR.
(Their present value is about their weight as waste-
(The word is "Stent,"
paper.)-CONSTANT READER.
and the query has been asked before. See Replies 37038,
p. 398, No. 744, Vol. XXIX.)-H. J. Y. (Many such
machines have been patented; you had better search at
the Patent Office Library, or get some one to do so for
you.)-PRINTFIELD. (The makers of your telescope are
still in business, and would doubtless supply what you
want, their address is St. Paul's Churchyard, London.)
-BAKER. (A brick oven would, we should suppose,
serve your purpose best, but your query is a vague one;
as to your second query, it is doubtless possible but
scarcely likely to be undertaken in these days of cheap
railway communication.)-N. J. RENNEY. (We have no
space to spare for directions for the perpetration of
practical jokes.)-W. H. T. (We know nothing of it,
and should certainly recommend Crossley's in prefer
ence.)-J. KYLE. (Poor soil and a late variety, no
doubt; but potatoes never do well in confined spaces.)
-S. A. STEWART. In type; we will send proof, if you
forward address.)

WEATHER. (See p. 553, Vol. XXIX., and many other
places. We believe you can get tables from the Meteoro-
logical Office, and they are given in the handbooks on
the subject.)-W. A. (The question has been fre
quently answered, but you can make your choice of
books by procuring Mr. Calve.t's catalogue from 99,
Great Jackson-street, Hulme, Manchester.)-A. L. C.
(Mix petroleum with a decoction of soapwort.)-AN
ENGLISH MECHANIC. (See p. 415, Vol. XXXII. It is
a matter for experiment. Trouvé's is the only instance
we know of, and that is described at place cited, and
is on view at the Paris Exhibition.)-M. B. (A series
of papers on "Examination of Living Objects Under the
Microscope" appeared on pp. 262, 288, 333, 433, Vol.
XXX. See also the indices of other volume:.)--JOSEPH
E. LYNDALL. (The capacity of haylofts is reckoned at
500 cubic feet per ton.)-VOLUNTEER SERGEANT. (See
p. 334, Vol. XXXII. Have you tried pipeclay or citric
acid? We are afraid you will have to send it to the
dyers.)-S. J. (Make the bit hot, file clean, dress with
flux, and rub over with solder. A shallow hole in a
brick, into which solder and flux are put, is the usual
thing. 2. See the index of the last volume under
Balance, and refer to the articles on Watch Repairing.)
-CHICK. (See p. 136, last week.)-THETA. (1. You
have omitted the word "whole." 2. Inserted. 3. Fre-
quently answered. See p. 580, last volume.)-A. (Toe
query is so indefinite that we can only refer you to the
textbooks and other works on the subject.)-ZEALOUS.
(A Leclanché is better adapted for such work than a
Daniel, but for the construction of either you must con-
sult the indices or refer to an elementary textbook.) -
ELECTRO. (Either a Daniel or a Smee. The former
consists of a copper plate immersed in a saturated solu-
tion of sulphate of copper, and a zinc plate immersed
in a solution of sulphuric acid, the plates being sep1-
rated by a porous partition. The Smee consists of a
plate of platinised silver between two zine plates. Many
forms of both have been described in back volumes.
They are to be bought as cheaply as they can be made.)
-MAGNET. (For a telephone, see the indices of the
last four or five volumes, and you will be able to make
a choice)-H. G. B. (See p. 332, last volume, and the
preceding answer.)-CARIOUS TEETH. (We answered
you on p. v., number for Oct. 7. You can stop them
yourself with the prepared guttapercha, sold at the drug-
gist's. We cannot discuss the fees of dentists.)-
J. A. M. (See recent numbers. It is not possible to
construct a small electric light at a moderate expense.
A dynamo-machine is the cheapest method of produ-
cing the current.-ALEXANDER. (Gannister is a highly
silicious fireclay, which is sometimes mixed with plastic
clay. It is used for lining Bessemer converters, &c.
Can be obtained at Sheffield, Middlesbrough, and other
towns where steel is made. It makes a most refractory
firebrick.) ABRACADABRA. (The answer depends
entirely on your personal tastes and capabilities)-
G. H. (See p. 73 about cleaning violin, and the indices
for varnishing.)-SILENT. (They are probably not set
properly; try lifting them up a little, or, if already high,
press them down. See many replies in back numbers.)
-LAD. Glasgow or Belfast. The premium would be
about £100 if a gentleman apprentice; if prepared to
"rough it," you might find a situation, especially if
you have had a little experience in a general engineer's
shop.)-A DYSPEPTIC. (Rather beyond our sphere. Of
course some have experienced benefit, or imagine they
have.)-J. H. (See p. 94, last volume. You must buy
the prepared rubber. It is mixed with sulphur, and is
vulcanised by beat. Naphtha has nothing to do with
the process)-VOLUSTEER. (There is nothing better
than camphor-smoking. Do you not understand that
if there were any permanent process, it would soon be
known amongst riflemen)-CIVILIAN. (Yes, all par-
ticulars can be had at any recruiting station.)-W.J. Holloway's Pills and Ointment. - Precious
GRIFFITHS. (Instructions for making small dynamo- Remedies.-Cramps, vomiting, and griping quickly yield to their
machines in Vol XXXI, pp. 116, 212, 236. Articles potent properties, the death like sickness passes away, and the
glow of health returns as the friction of the ointment causes the
on Mechanical Drawing commenced in No. 851.)- irritated nerves to become soothed and calmed, In local inflam
PUZZLED. (The ink is forced into the graved lines, themation they act like a charm.

W. SEEKIN.-A Brother Reader.-Geometricus.-Annie Kindersley.-Poor Man.-Your queries can only appear in the "Sixpenny Sale Column."

NOTICE TO SUBSCRIBERS. Subscribers receiving their copies direct from the once are reguested to observe that the last number of the term for which their subscription is paid will be forwarded to them in a Fix Wrapper, as an intimation that a fresh remittance is necessary, if it is desired to continue the Subscription.

The English Mechanic

AND

WORLD OF SCIENCE AND ART.

FRIDAY, OCTOBER 28, 1881.

THE APERTURE OF MICROSCOPE-
OBJECTIVES.-VII.

E are now able to sum up, very briefly, Aperture.

It is important to bear in mind at the outset that there are two entirely distinct branches of the question. The first relates to the definition of aperture, and the mode in which it is to be estimated; whilst the second explains the proper function of aperture.

It has been shown that:-
:-

I. The true definition of "aperture" in a microscope-objective must obviously refer to its primary meaning of "opening"to the capacity of the objective for receiving rays from the object and transmitting them to the image. If, all other things being equal, one objective is found to receive and transmit more rays than another, it must necessarily have a larger aperture.

In regard to the estimation of aperture, a very simple consideration shows that as in a single lens its aperture is determined by the ratio between the utilised opening of the lens and its focal length, so in a compound objective it is determined by the ratio between the utilised diameter of the back lens and the focal length of the objective.*

This ratio is expressed for all media and all cases by n sin u, where n is the refractive index of the medium (air or immersionfluids), and u the semi-angle of aperture of the objective, the values of n sin u for any particular case giving the "numerical aperture, or true aperture, of the objective.

Whether we have an air, water, or oil objective, its angular aperture cannot, of course, ever exceed 180°, sin u then being 10. The indices of air, water, and oil (=n, the other term of n sin u) are, however, 1.0, 1.33, and 1.52. In the case of an air objective of maximum aperture, therefore, n sin u cannot exceed 1.0; while, with a similar water or oil objective it may be 1.33, or 1:52; so that the apertures of water and oil objectives may exceed those of air objectives by 33 per cent. and 52 per cent. respectively, there being in fact a progressive increase in aperture from the lowest air-angle to its maximum of 180°, and thence to the highest water and oil angles.

To express aperture by the angles of the incident rays is, therefore, obviously misleading, for even when the medium is the same, twice the angle does not represent twice the effect, while when the media are different we have two identical sets of figures which, nevertheless, represent not identical, but different, effects.

These simple considerations dispose of the volumes of controversy that were for years written on the "aperture question," and the erroneous supposition that the aperture of an air-objective of 180° angle must represent the greatest possible aperture obtainable,

If, therefore, two objectives have the same focal lengths, their apertures will vary with the utilised diameters of the back lenses. Thus, if these are as 2:1, the aperture of one objective will be double that of the other. If the two objectives have different focal lengths (as in, and in.) and different back lenses, then if the latter are in the ratio of the focal lengths (i..., 2:1), the apertures will be identical; or if they are not in that ratio (say, 3:2), the apertures must be different (12: 16 or 3:4). If the back lenses are the same, the apertures will be inversely as the focal lengths (i.e., as 1:2). VOL. XXXIV.-NO. 866.

and one which could not be exceeded, but
at most only equalled, by immersion ob-
jectives.*

II. The second branch of the aperture
question with which we have dealt-viz.,
the function of aperture, must, as we have
said, be kept entirely distinct from the first.
While even the tyro in microscopy cannot
fail to recognise the fact of the increase in
the aperture of objectives, when we pass from
air to media of higher refractive index, it
is otherwise with the second branch of the

The theory of microscopical vision propounded by Professor Abbe may be summarised thus:

Coarse objects are depicted by the microscope practically in accordance with the laws of ordinary vision, and the image corresponds with the object.

In the case of minute objects, however, those laws cease to be applicable, and the object is imaged by rays which in their passage through it are each spread out by diffraction into a fan or group, the smaller

subject, which depends upon much deeper the object the wider being the spread of the
optical and physical laws, and notably upon fan.
the phenomena of diffraction.

In order that the image should in this
The first branch is wholly independent of case exactly correspond with the object, all
any theory of diffraction. If diffraction the diffracted rays must be gathered up by
phenomena did not exist, or if they were the objective. If any are lost we then get,
proved to have been misinterpreted, the fact not an image of the real object, but of one
of the increase of the apertures of objectives which would give just those diffracted
with the increase in the refractive index of rays which are actually taken up by the
the immersion fluid would still be beyond objective.
dispute.

it was always tacitly assumed that the "angular aper-
• Much of the confusion can be traced to the fact that
ture" of an objective represented its real aperture, and
prior to Professor Abbe it apparently did not occur to
anyone that the so-called "angular aperture was only
one of the factors that determined the true aperture.

An experimental proof of this view is the image of a known object some of its diffurnished by artificially shutting off from fracted rays, when various false appearances will be presented by the microscope, none of which could have been recognised as

spurious if we had not had the known object to check them by.

It is, therefore, impossible to determine by mere visual inspection through the microscope what is the actual structure of the minuter diatom valves and similar objects.

The theory furnishes an explanation of the increased power of vision obtained by increase of aperture in the case of minute objects. A small aperture can admit only a fractional part of the diffraction fan emanating from the object to admit the whole or a very large part, and consequently to see the minute structure of the object, or to see it truly, a large aperture is necessary, and in this lies the value of a wide-angled immersion objective for the observation of very minute objects.

We append the very useful aperture table computed by Mr. Stephenson, which is printed with each issue of the Journal of the Royal Microscopical Society."

REVIEWS.

Hydraulic, Steam, and Hand-Power Lifting and Pressing Machinery. By FREDERICK COLYER, M.Inst. C.E., M.Inst.M.E. London: E. and F. N. Spon.

on the assayer's art has been revised and tation put before teachers to give their
brought abreast with the progress of pupils just that information which they
chemical science. The volume, therefore, know is required to pass the examination,
contains a number of additions and improve- at the sacrifice, it may be, of that sound
ments in processes, to make room for which knowledge of principles which, for future
the older methods have been omitted, the work, is alone valuable, and he has con-
editor's object being not to fill his pages trived to present his subject in such a
with descriptions of all the processes, but to manner that the student who will carefully
present the reader with such as are found read through it, and make the experiments
most useful in differing circumstances. The described, will be in a position to pass the
new chemical nomenclature and notation examination, or to proceed at once to the
have been introduced in the present edition, standard works on the science. Laboratory
which will no doubt meet with the same hints are given here and there, and illus-
favour from practical assayers as was trations help to explain how the operations
accorded to the previous editions. One are carried out.
objection will be made by some of those who
really use the book, and that is both
English and metric weights are used; but it
may be urged that to convert all the weights
and measures as given by the author in his
original work would involve a great deal of
labour, while to translate the metric mea-
sures into English whenever new matter is
added, would be a retrograde step, and in-

crease the risk of error.

Elementary Treatise on Physics. Translated
and Edited by E. ATKINSON, PH.D. Tenth
Edition, revised and enlarged. London:
Longmans.

THE popularity of "Ganot's Physics" is attested by the fact that the tenth edition has been recently issued, although the ninth was published less than two years previously. That the new edition is not a mere reprint, is shown by the facts that it conTechnical Vocabulary. By Dr. F. J. WERS-tains more pages than the ninth, and that HOVEN. London: Hachette and Co. the revision and enlargement commence on TECHNOLOGICAL dictionaries are of necessity P. 2, in article 3. So on throughout the very difficult works to compile, and it is not whole of the volume, which now comprises surprising that some of those already in nearly 1,000 pages, illustrated by 844 woodTHI HIS work will be found useful not only to existence contain numbers of errors which cuts and four coloured plates, the work of engineers, but also to architects, as it will are not unfrequently amusing. Technical revision and addition has been carried out act as a guide in all cases where lifting or terms, especially those which are peculiar to wherever necessary or advisable. Such pressing machinery is to be erected. As the a trade or to a workshop, are not usually inventions and discoveries, for instance, as book is intended for practical men, the sub- found in dictionaries, and to accurately Hughes's Induction Balance, and Graham jects have been treated very concisely, mere translate them into their equivalents in Bell's Photophone, are illustrated and derudimentary description being entirely French, German, or other European lan- scribed as fully as possible, consistent with omitted, and discussion of the comparative guages necessitates a special research or the the elementary character of the work. value of certain machines limited to the mini- assistance of a large number of editors. A Pocket Guide to British Ferns. By MARIAN mum. Nearly all the apparatus described, Dr. Wershoven's little book makes no preS. RIDLEY. London: David Bogue. with the exception of certain specially men- tentions to the dignity of a dictionary, but tioned machines, have been personally it is an excellent vocabulary for the use of THE authoress having experienced a diffiexamined, experimented with, or erected students who can read French and for culty in determining the genera and species by the author. The volume is made up of visitors to technical exhibitions. The one while specifying the peculiarities in detail, of ferns, because writers on the subject, 120 pages of text, and 73 plates of litho- objection to it is that from the arrangement omit the decided special features or chagraphs, and is well adapted as a suggestive adopted the terms require looking for, but textbook for engineers and others. Hy- the author has contrived to bring all the racters which would guide the amateur draulic power is now applied in so many terms relating to one department together, book for the use of those commencing botanist in his work, compiled this little cases, and is withal found so useful and so so as to economise time as much as possible. the study of ferns, who often give up the little trouble (except in very cold weather), Thus under the head of " Workshop," the that such a book as this will no doubt be various parts and tools connected with a this volume is intended to remove. The pursuit on account of the difficulties which welcomed by the profession, especially as it lathe are arranged together, without, howwill enable them to decide where to prefer ever, any order of sequence. Besides tech-plan adopted by the authoress is to put down steam appliances. draulic lifting, the cost of pumping is about even whole sentences, descriptive of opera- the description of each fern occupies a page, In high-pressure hy-nical terms, the author gives phrases, and in a tabular form the characters of the different ferns: thus, in the book before us, 108. per 1,000 gallons, and the usual maxi- tions, which will undoubtedly be found use- the features being printed at the side in such mum pressure is 750lb. to the square inch; ful; but the person who sets out to use the but on a small scale for supplying a few book should familiarise himself with its a manner that its peculiarities can be taken in almost at a glance. In black type at the cranes, the cost may run up to 12s. and 14s. contents before he actually needs its serside we find " generic characters,' per 1,500 gallons. The cost of lifting, say vices. In about 300 pages the book before tinctive specific characters," "rhizome or at docks, and similar places, is about us contains a number of words and phrases caudex," stipes and rachis," and so on, 14. per 100 foot-tons, if in constant of constant occurrence in works on physics to "where found," and general rework; but for railway goods stations and mechanics, on gas-making, glass, pot-marks," and opposite these we find the it is probably 3d. per 100 foot-tons. Com-tery, paper, and beer manufacture. peculiar or special features briefly stated. pared with hand-power, the hydraulic machinery costs id. a ton for labour, Inorganic Chemistry. By WM. JAGO, F.C.S., The introductory and explanatory chapters, London: Longmans. with glossary, key to the genera, and an whereas the former is rarely less than 3d. per ton, and the speed of working is scarcely THE multiplication of textbooks for the index, will render this little book very welcome to those who are seeking to gain comparable. The work includes descrip- benefit of students in science classes may tions and plates of all the usual forms of be taken as evidence of the popular interest such a knowledge of British ferns as will hydraulic and steam-lifting machines, hand- in the study of scientific subjects; but if enable them to class them in their respective and determine the species. teacher" of, genera say, power lifting machines, and hydraulic- every

"certificated

pressing machines, with accounts of such chemistry, wrote a textbook, students would
appliances as Clark and Standfield's canal have some difficulty in deciding which to
and railway lifts for shifting barges and chose. Unless, then, we find a new textbook
trains bodily. The lithographed plates show is in some respects superior to the existing
the apparatus to a good-sized scale, and the
text is in clear type, though disfigured by
such printer's errors as "rivetted" and "des-
moate,"

A Manual of Practical Assaying. By Jonn
MITCHELL. Edited by William Crookes,
F.R.S. London: Longmans.
Tux fifth edition of this well-known manual
15 must be borne in mind in using the column of
"penetrating power" (which is in inverse ratio to the
numerical aperture a) that several other data besides
en to make up the total depth of vision of the micro-
Journ, &, Micr. 8oo., I. (1581), pp. 881-2.

"dis

We have also received The Unicorn, by ROBERT BROWN, jun., F.S.A. (Longmans), a mythological investigation, and a contribution to the science of psychology, in which the author traces the origin of a number of old legends, and apparently arrives at the conclusion that the sun is the lion and the moon the unicorn.-Hunter and the Stag (Williams and Norgate) is a letter to Prof. Owen, by CHARLES ADAMS, in which the writer replies to the address which Prof.

works, or puts old facts in a better way, we
are inclined to look upon it as a bit of pro-
fessional advertising. We have already too
many textbooks
specially adapted" to
the wants of students connected with the
Science and Art Department; but we can
make room for Mr. Jago's volume, because
although primarily designed for students of Owen delivered at the unveiling of the
the science classes, it is really an elementary
textbook of the science of chemistry that
will be found useful by those who are not
cramming for an examination, and have not
the benefit of personal instruction from the
teacher. The author is aware of the temp-

Harvey Memorial, and demolishes the argument of the vivisectionists based upon Hunter's alleged discovery.--Practical Chemistry, by J. HOWARD, F.C.S. (Colling Sons and Co.) is a new and revised edition of one of the publishers' elementary scie

C. Detaille.

series. Handbook of the Economic Ster-pany, Limited. Diploma of honour awarded to 1 a.m. on the 8th, between two and three hours ling-Silver Newtonian, by A. J. S., is inventors: Sir William Thomson, Hughes. prior to which he will Transit the Sun's disc. a tractate by our well-known correspondent, Diploma of Co-operation: King's College, Royal As the last-named phenomenon, however, does in which he sets forth his system of making Institution of Great Britain. Gold Medals: not begin until 10h. 16m. 13s. p.m. G.M.T., it sterling silver Newtonians. It is illustrated Brush Electric Light, Bright, British Electric will obviously be invisible in this country. by several engravings and a photographic Light Company, Elliott Brothers, Indiarubber Mercury attains his greatest elongation West frontispiece: The Use and Adjustment of Muirhead, and Company, J. W. Swan. and Telegraph Compary; Latimer Clark, (19° 52') at 8 p.m. on the 24th. His considerable, the Silver-on-Glass Reflecting Telescope, by and late in the month again increasing, South F. E. FAHRIG and Co., Southampton, is Declination, though, at this time, immerses him in the mists of the autumn horizon; and he is sufficiently described by its title. very indifferently placed for the observer. His brochure also contains the price-list of the angular diameter increases from 9.4" on the first publishers.-The Furniture Trade Catato 9.8" on the 7th, and then decreases again to logue (Wyman and Sons) is a handsome 6" by the end of the month. volume of plates containing designs for every description of modern furniture of the styles in general demand. It is a volume that will be appreciated by furniture dealers and their customers at home and abroad.

THE PARIS ELECTRICAL
EXHIBITION.-IX.

The

THE Congress is closed, the awards have been distributed, the Exhibition is manifestly

Day of Month.

ASTRONOMICAL NOTES FOR
NOVEMBER, 1881.
The Sun.

Souths.

At Greenwich Mean Noon.

Day of

Month.

Declination
South.

Souths.

h. m.

0 36.4 p.m. 11 57-4 a.m. 11 15.0 10 44.8 ""

Right
Ascension.

h. m.

14 27 21 14 34 48 14 43 38.54
14 47 816 7 25 15 3 21.31
15 7 16 17 33 19 15 23 4.09
15 27 46 18 51 39 15 42 46.87

26

12 19-3 14 33.5 12 28.4 14 51.3 14 2.3

10 31.3 "" 10 29.3 ""

h. m. 8. a.m h. m. s. 111 43 42-36

611 43 46 79

drawing to its end, although the exact date of
closure is not known. The following decisions 1111 44 12-15
have been taken by the Congress:-

1. The centimeter-gramme second system (C.G.S.) will be adopted for electrical measures. 2. The ohm and volt remain as before.

3. The ohm will be represented by a column of mercury Imm. square in section, at the temperature of 0.C. An international commission will determine its length.

4. An ampère is the current produced by an electro-motive force of one volt through a resistance of one ohm.

5. A coulomb is the quantity of electricity defined by the conditions that in the current of one ampère one coulomb per second pass the section of the conductor.

6 A farad is defined by the condition that, a coulomb in a condenser, whose capacity is one farad, establishes between the armatures a difference of potential of one volt. The farad remains as defined by the British Association. It will be observed that the ampère is identical with the British weber. The name has been changed in order to avoid confusion with the German weber.

The following resolutions have also been taken by the Congress :

source of

16 11 44 59.05
21 11 46 7.23
26 11 47 35 36

13

13 58.2

h. m.
12 48.5
13 11.5
34.7 8
10 24-2

3 25.1
5 47.8
8.0

11

19.4

3

56.3 a.m.

10 11.9 10 15.7 10 19.9 10 24:5

7 33.1 39

11 34.5 ""

4 24.0 p.m.

Establishment of an international commission for determining electrical units; for the study of terrestrial currents; for the study of atmospherical electricity; of lightning-conductors; are telegraph and telephone-wires a danger or of protection against lightning? All diameters of telegraph wires to be designated in millimeters, without reference to any gauge; at 8 p.m. on the 5th; with Jupiter at 6 p.m. on The Moon will be in conjunction with Saturn comparisons of electric light to be made with the the 6th; with Mars at 11 p.m. on the 10th; Carcel lamp; an international commission is to with Venus at 1 a.m. on the 20th; and with determine the unity of light; the Congress hopes that steps will be taken by each Govern- Mercury at 8 o'clock the same morning. ment, in order to insure the inviolability of submarine cables.

The

The electric light has been experimented with at the Opéra with much success. The great staircase was lit up by 32 Brush lamps, fed by machines at the Exhibition. The total length of the Brush cable was about 6 kilométres. foyer was lighted, partly by gas and partly by Edison's lamp. It was very difficult to judge of the electric light in this way, but the moment the current was turned off it was very easy to see that the thin threads of incandescent carbon afforded the best part of the light. The interior of the theatre was lighted by 54 Jablochkoff candles; Maxim's lamps were very brilliant in the two small saloons on each side of the foyer; Swan's lamps were also mixed with the gas flames of the lustre. The buffet was very nicely lit up by Jaspar's system, to which I have already referred in a former article.

Hence, it will be seen that Venus travels from Virgo into Libra. She will be very close to Virwill be seen 4° North of Spica on that of the ginis during the Early Morning of the 4th, and 8th. After this, her path lies through a region void of conspicuous stars until the 26th, when

she will be less than 1° North of a Libra. Occultations of (and near approaches to) Fixed Stars by the Moon.

Name of
Star.

†6 10 S. by E.
+9 7 p.m.
N.
11 54 Bright.
4 +1 10 a.m. S.
2 4 Bright.
+12 43 p.m. S. by W.
1 30 a.m. Bright.

89

177
130
46

2 59 a.m. *Dark
625

239 Dark 285

324

185

143

78

39

+4 53 p.m. 8. by E.

5 5 7 36 5 15 11 28

Dark 128

Dark 61

151 89 Dark 101 82 Dark 111 147

Dark 241 210 290

21

† Near approaches. But apparently bright.

Mercury

Grand diploma of honour to the British Post-
office. Diploma of honour: Society of Telegraph
Engineers and Electricians. Diploma of honour
for industrial establishments: Eastern Telegraph
Company, Siemens Brothers and Company, Sets after the Sun for the first four days of the
Limited Submarine Telegraph Company; month, later on becoming a Morning Star. He
Telegraph Construction and Maintenance Com- comes into inferior conjunction with the Sun at

Bright. 319 312 Bright. 295 334

Jupiter

Vertex.

Is visible from sunset to dawn, and, coming into opposition to the Sun at 9 a.m. on the 13th, with very considerable North Declination, is about as

39 P.M. 211AM

32 P.M.

Ee Eclipse; Oc Occultation; Tr Transit of Satellite; Sh Transit of Shadow; D Disappearance R Reappearance; I Ingress; E Egress. The printing of a phenomenon in italics indicates that its visibility is rendered doubtful, either by the brightness of the twilight or by Jupiter's proximity to the horizon. The student should carefully observe the Transits of Satellite III. on the nights of the 18th and 25th, and note whether any (and if any, what) change of colour occurs in the Satellite as it crosses Jupiter's disc.

Day of

Month.

Greenwich Mean Time of Southing of Fourteen of the Principal Fixed Stars on the night of November 1st, 1881.

Star

a Capricorni
a Cygni

Neptune.

Right
Ascension.

Declination
North.

Souths.

1

h. m.
253.6
2 53-1

11

2.52.5

16

2 52-0

14 40.9
14 38.5
14 36-1
14 33-7

h. m.
12
11 47.8

11 27-6

10 27.0

8.0 p.m.

a Cephei

a Aquarii
Fomalhaut
Markab..

Piscium

5.52 48.34 29

6 31 3-76

7.14 54-10

8

6 10-28 11

8 13 54-46 "

8 48 48-72

9 17 8.90, 9 48 36-467 10 31

8.54,,

11 15 3.80 " 12 10 29.85", .. 12 30 15-09 " .. 12 54 44.32 99 The Method of finding the Greenwich Mean Time of Southing of either of the Stars in the above List, for any other night in November, as also that of determining the instant of its Local Transit at any other station, will be found on p. 390 of Vol. XXXII. The rules there given, however, are not rigidly accurate when applied to Polaris and other circumpolar stars, although they are sufficiently so for all ordinary purposes.

Shooting Stars

There seems but little need to retell here the strange story of the great Meteoric stream through which the Earth travels from the 12th to the 15th of November, nor to repeat the history of Professor Adams's identification of this ring of aerolites with the little comet discovered by Tempel in 1866. Suffice it, then, to say that 11 19.8 p.m. this annulus of discrete matter revolving round the Sun and intersecting the orbit of the Earth, possesses one region of exceptional richness; but, as it describes its path in 33 years, that period must always elapse between two displays Her limited path this month lies wholly in of extraordinary brilliance. As the last of these

h.

m.

7 2 28.9

3

43.3

17

2 19.7

25.6

10 31.3

27

2 12-3

222

Cetus.

occurred in the year 1866 (oddly enough the