and the screw produced will be the same must be always used for cutting such work, he is driving a locomotive of the ordinary type. as the slide-rest screw, and this must and the velocity at which it is driven must M. Mallet contends, on the other hand, that be, as before stated, 10 to the inch. The be governed by the material used. I have it is necessary that compound locomotives difference in the pitch of the screws or now an arrangement to my best slide-rests should be so arranged as to work when required spirals is obtained by the difference that will admit of the operator simply as non-compound, and that any simplifiof the extreme wheels-viz., that on looking on when all the apparatus is set, cation of gear which involves the engine the chuck and slide-rest screw, the number and it is simply that the main screw of the always working as a compound is paid for of teeth in the intermediate wheel signify rest is worked by a tangent screw from the at too high a price. The fact that English nothing so long as all are in one plane, and over-head very slowly at the same time as locomotives designers have been aware of if only one is placed between those on the the drill is running at a high speed from the existence of the compounds and their chuck and slide-rest the spiral produced will the same driving power. I have cut a alleged economy without making, so far as be right-handed; but to make the same spiral 12in. long without turning a handle, we are aware, the slightest sign of adopting left-handed, it is necessary to place and have found it a great saving of labour, the improvement, might be regarded as the arbor with permanent pinion of 30 teeth, and I can safely say that the action is more sufficient expression of their opinion, did we Fig. 6, between, in order to reverse the regular than that obtained by the hand; not know that the official railway mind movement of slide-rest screw. however, I will not say more upon this now, is essentially conservative, and not given to as I hope to give an illustration of the slide-exploiting far from the beaten track; but it rest at some future period.

It will be observed that the holes in the large wheels are different in size to those in the pinion, Fig. 8, the former being bored out to our standard size of 14in., the lathe

is not impossible that in this case engineers in this country, taking the 20 per cent. of coal saved with a grain of salt, may look

being in. diameter. The brass bush, Fig. COMPOUND AND FOUR-CYLINDER upon a compound locomotive as rather too

7, is fitted to the larger holes, and the hole in it is then fitted to the arbor. The large wheels are not so thick as the smaller pinions, the object of this being to allow of the face of bush, Fig. 7, being admitted; it is a nice point in fitting up an apparatus of this kind to have all the wheels in line perfectly, and when the double arbor is employed it requires extra care in the length of the different parts.

There is naturally a little management required in choosing wheels that will admit of the slide-rest being brought up to its work; but the wheels may be changed without interfering with the actual screw or spiral, so long as the ratio is unaltered, and, I may say, that no great difficulty will attend the choice. By way of example, if only two wheels are employed as the train, that is to say, one on the spiral chuck, and one on the slide-rest, all such wheels as may be termed pairs, that is, the one having double the number of teeth that the other has-for example, 15 and 30, 18 and 36, 36 and 72, 48 and 96, 60 and 120, 72 and 144. These numbers, it will be obvious, represent a proportion of one to two, and will, of course, all produce the same relative velocity, and should any of the former of these pairs be used, the screw cut will have twice the number of threads of that in the sliderest, viz., 20 instead of 10 threads. The choice of which pair of wheels are to be used will simply concern the accommodating of the slide-rest to the axis of the lathe. These remarks as to relative distance of slide-rest from lathe-centres of course apply to all the arbors, whether single, double, or perma

THER

LOCOMOTIVES.

much of a good thing. Granting all that can be said in favour of expanding steam HE question has been often asked in in two cylinders instead of one, it is not engineering circles why, if the com- quite clear on which side the advantage lies pound system is so economical and advan- when all the points are considered; for in a tageous in the case of marine engines, it has locomotive there are many things to be not been introduced with more success in thought of besides mere economy, even the case of locomotives. The ready answer when the latter is so large as 20 per cent., is invariably that it is too complicated, and which would clearly mean a very large sum that the advantages to be obtained will not to some of our companies. When, however, compensate for the extra cost and the extra so little is done to preserve the steam from care needed. The locomotive is already a the cooling influence of the cylinders, it is complicated machine, which often moves at scarcely worth while to complicate the a high speed, and designers, at all events in machine by the introduction of two this country, have a decided and not un- extra cylinders and special valve-gearing natural aversion to the introduction of merely for the sake of saving a few coals. even an extra bolt. Nevertheless, So If the extra cylinders are to be introduced, long ago as 1876, M. A. Mallet, of most engineers would declare in favour of Paris, having successfully adopted the com- using them for balancing purposes, as the pound system on the Bayonne-Biarritz line, most direct way to secure economy, by savendeavoured to introduce compound loco-ing wear and tear, and by conducing to motives in Germany, but not meeting with safety. As locomotives are now generally much encouragement, he did not take out a constructed, there is no attempt made to patent in that country. Since then, at least heat the cylinders, with the view of preventone firm of German engineers has turned its ing condensation; and, in some cases, very attention to the subject, and has produced little is done to prevent radiation and coolcompound locomotives for which a saving of ing by contact with the atmosphere a source fuel ranging from 16 to 20 per cent. has of, possibly, greater loss than the gain to be been claimed, besides an appreciable obtained by compounding. It is incontesteconomy in oil. It seems obvious that if by able that, if the steam is exhausted from one compounding marine engines a saving can cylinder to another, the first cylinder is not be effected-if in fact the compound engine cooled down so much as it would be if the is more economical than the single type- steam exhausted direct into the air; but the there is no valid reason why the system economy to be obtained by the former should not be applied to the locomotive, for method of treating the steam is only that the mechanical details will not long puzzle which is due to the greater degree of expanthe skilled engineer. M. Mallet has, sion, less the extra back-pressure caused we believe, supplied designs for compound by the transference of the steam from locomotives, which are now running in Spain, one cylinder to another; and, when the In addition to right- and left-hand screws Austria, and Russia, besides those on the compounding does nothing more for the or spirals, it is no difficult matter to produce Biarritz and other French lines, a principal locomotive, it may be justly regarded as a double, triple, and quadruple, in fact, any feature of his engines being that they can very doubtful advantage. If it reduced number of threads. When the apparatus be worked either compound or single, at the strains and made the engine run easier and was first introduced years ago, it was, of will of the driver. A self-acting reducing- steadier, the 'improvement "' would not course, not nearly so complete as it is in the valve insures an equality of effort in the two have been left entirely in the hands of present day, and the only means of dividing cylinders when working compounded-an foreigners, for if engineers are conservative the work into double or triple threads was arrangement which is said to give excellent here, they are sufficiently go-ahead in by shifting the wheels-that is, the teeth results. The firm of F. Schichau, Elbing, America to have at least made the experiwere marked and the one shifted round so Germany, who appear to have taken up the ment. On the contrary, there they have many each time; but this, I need scarcely subject after M. Mallet had made his pre- also turned the cold shoulder to the comsay, has been obsolete now for a very long liminary trials, simplify the arrangement by pound locomotive, while at least one of their time, and the dividing is effected by means so constructing the valve-gear that the number has taken up the idea exhibited by of spiral chuck, Fig. 3. This, it will be engines always work compound. The Mr. Haswell, of Vienna, in the London seen, has a revolving wheel with 96 teeth German firm contends that the manipulation Exhibition of 1862-viz., four cylinders, and a detent, so that it would be possible to of the valve-gear must remain as simple as the pistons of which receive steam simuleven cut a spiral with 96 separate threads; it is in the ordinary locomotive, the relative taneously on each side, one moving in one but this, of course I only mention as best degrees of cut-off in both cylinders direction and one in the opposite. In illustrative of the action of the chuck being determined once for all, so as to be Haswell's locomotive the cylinders were to make it more clear. We will as-made automatically and in such a manner arranged two on each side of the engine, sume that a screw with four threads is that any interference on the part of the connecting-rods being coupled to cranks required; it will then only remain to divide the driver is prevented. For obvious placed opposite one another. The object the wheel into four parts, 96, 22, 24, 48, reasons that is advisable, as it is of of the designer-almost perfect balancing, the 96 being the starting-point; but it is in the first importance that the work done with the consequent great steadiness in ornamental turning that the spiral appa- in the small cylinder should be as nearly as running-was attained; but the complicaratus is so useful and so highly appreciated possible equal to that done in the large tion of machinery was found to be so disby our amateur turners, and it is when such cylinder, in order to insure an equalisation advantageous that this type of engine spirals as are required for the purpose of orna- of strains. This object has been accom- never became more than an experiment. mentation are produced that they are called plished by simple means, and in such a Nearly twenty years after the exhibition Elizabethau twists, and referring to my manner that the driver himself, for all he of Haswell's locomotive, we hear that his former remarks, a drill or universal cutter can find out on the foot-plate, may believe idea has been taken up in America by

nent.

Mr. H.F. Shaw, of Roxbury, Mass., who has
designed a four-cylinder engine, which,
according to report, does excellent work at
high speeds, with more economy than the
ordinary type of locomotives. So far as the
frame, boiler, and truck are concerned, the
engine is of a common class turned out at the
Hinkley Works, Boston; but instead of two
cylinders 16in. by 24in., it has four, which
are 10 in. by 24in., and which, being con-
tained in two castings, do not materially
increase the width of the engine. The in-
crease of piston-area thus obtained is as 346
to 201, while the space occupied is increased
by about 6in. in one direction, and reduced
in another. Each couple of cylinders is
supplied with steam through one valve, TOOLS AND MOTIVE POWER FOR
operated by the usual link-motion and
rock-bar. This valve, which is one of the

to

minutes-a rate certainly not remarkable for before finally tightening the bolts, and any error
high speed, but which is two minutes under in the adjustment corrected. We have now the
schedule time. Probably, if the task were means of using the power of the engine at any
set, the locomotive could do much better desired part of the shop, and having determined
than that, and we shall no doubt hear before upon the locality of our lathe, let that be the
long further particulars of its performances, before said that the lathe should be placed in
first tool to apply power to. I think I have
which will, we think, be read with more front of a window so as to get the light direct
attention than those of compound locomo- on to the work; no other position is satisfactory.
tives, which simply complicate the existing Our first business is to determine the speeds at
designs without introducing any advantage which to drive the lathe; without gearing, these
besides a small economy in fuel, that is speeds should range from 250 to 800 or there-
probably swallowed up in the extra repairs abouts. I cannot give more than these general
and first cost of the engine.
figures, because the circumstances of each indi-
vidual shop will necessarily vary so much, so
that the calculations must be made by the work-
man himself. Suffice it to say that what is
called a countershaft must be fixed above the
lathe and parallel with the main driving-shaft;
the bearings of this shaft may conveniently be
mounted in brokets of wrought-iron, about
of the ordinary form shown (shaded) in Fig. 18,
14in. by in., and secured to the beams of the
shop by coach-screws or bolts; these brackets
are tied together at the side nearest window by
a transverse bar, upon which is pivoted a shift-

AMATEURS.-XIV.

Ait becomes necessary to provide shafting
and pulleys, through which to convey its power
to the various machines in the shop. A main
driving-shaft should run almost the entire
length of the shop, or within about 4ft. of it;
upon this shaft, which may be lin. or 1in. in
diameter, pulleys or "drums" of different sizes
are keyed; the one at the end being fixed over
the engine-pulley passes up over it. An approxi-
the engine, so that the main driving-belt from
mate calculation must be made of the speed of
the engine, and the pulleys must be arranged so
that the main shaft revolves at about two-thirds
of this quantity: thus supposing the pulley on
the engine to be 8in., that on the main shaft
must be 12in. The average speed of one of these
small engines is 250 revolutions per minute, so
that the main shaft revolves at about 160 per
minute; it is well to know within a little how
quickly this revolves, as the pulleys can then be
desired to drive. All the drums on this shaft
easily calculated for any machine it may be
are double the width, on the face, of the belt they
are intended to carry, and turned parallel on the
faces, excepting the one at the end, which needs
to be only the width of that on the engine-i.e.,
about 1in., and turned slightly convex,
because the belt always seeks to run on the
highest part of a pulley, and if this be the middle
of the face, it follows that the belt is less likely

FTER the engine has been fixed in its place

to run off. We must now consider the means to

employ for getting this main shaft in line with
is intended to run in brass bearings seated into
the engine-shaft. Let us suppose that the shaft
hangers of a pattern similar to Fig. 17; it will

most important features of the locomotive,
is of the plain D type at one end, while at the
other it is a B valve with a bridge, the
steam entering one cylinder in the ordinary
way, and passing under the valve to reach
the other cylinder, both, as mentioned above,
taking steam simultaneously. Two valves
would be objectionable, because they would
unnecessarily complicate the gear and be
more liable to derangement; but it was
thought that the difference of friction at the
two ends of the single valve, owing to the
steam passing under it at one end, would
tend to slew it out of position, and also
cause excessive friction between valve and
seat. The result of a practical trial shows
that the valve works as easily as the usual
plain D valve, and, apparently, with no more
friction-probably less, because the steam
being admitted at one end under the valve
would necessarily help to balance it. The
exhaust is indistinguishable from that of
an ordinary locomotive, for the simple
reason that each couple of cylinders ex-
hausts at the same instant. The driving-
wheels are accurately balanced, but are cast
without counterbalance weights, except that
there are two crankpin bosses, one to
receive the
the
pin, and
other
act as
balancing
a
weight. The
crank is double, of wrought iron, working
in a substantial centre - bearing held in
pedestal jaws attached to a girder suspended
from the main frame. By this arrangement
the action on each side of the engine is the
same: one piston is pulling the wheels round
while the other is pushing them round; thus
nearly all the power of the steam is exerted
in rotating the driving-wheels; but with the
ordinary arrangement, the power applied to
the piston is necessarily transmitted to the
bearings as well as to the crank, and there
is consequently undue friction and rapid
wear of the parts. It is tolerably clear that
the swaying motion of the engine, specially
noticeable in the case of locomotives with
outside cylinders, must be almost entirely
avoided when the action is balanced
as it is in these four cylinder engines,
and experiments with the "H. F. Shaw"
fully bear out theory, for we learn
that with the throttle valve fully
open and 130lb. of steam, the driving-
wheels did not slip, and no swaying from
side to side was noticeable, although heavy
train was attached. The total weight of be seen that the shaft can be lifted down at any
time for alteration, or substitution of drums and
engine alone in working order is a little over pulleys, and is thus the most advantageous form
33 tons; the driving-wheels are 63in. in to select. I should recommend the following
diameter, four coupled, with a leading four-plan to be adopted: stretch a piece of cord
wheeled truck; the locomotive presenting tightly the entire length of the shop, near the
to the uninitiated the ordinary appearance floor, and carefully adjusted at each end, so that
of a common type of American engine, ex- it shall be exactly parallel with the engine-
cept that the peculiarity of the cranks would shaft; this need not be very difficult to arrive at,
catch the eye of the observer. The object if a long, straight rod be placed in the bearings
of the experiment is high speed with safety; of the engine, from which the crank-shaft, etc.,
that has been attained, and economy of fuel have been temporarily removed. Now sling the
as well: it remains to be proved how the shaft from the cross-beams of the shop and ad-
engine will stand on the repair list when it level, until it is true with the line, and also truly
just it by means of a plumb-line and a spirit-
has been fairly tested over a number of horizontal. It will not now be difficult to sub-
It frequently takes a train stitute a permanent hanger for the temporary
composed of five cars, two of them " palace," slings; and as these hangers have certain powers
from Boston to Providence, 444 miles, in 57 of adjustment, the shaft must be tried again

miles run.

FIG.17

FIC.18

FIC./9

ing-fork shown in Figs. 18 and 19: any similar
arrangement will do, but sliding-bars carrying
the fork are generally noisy. The shaft itself
need not be more than 1in. diameter, as its
length is but short; it carries upon it fast and
loose pulleys, and a cone pulley the counterpart
of the one upon the lathe. The fast pulley, as
its name implies, is keyed fast upon the shaft,
the loose one being free to revolve, whilst pre-
vented from endlong motion by the abutment on
the one side by the boss of the fast pulley, and
on the other by a collar bored to the size of the
shaft and fixed by a set-screw.
W. S. Brown.
(To be continued.)

DR: DUDGEON'S POCKET SPHYGMOGRAPH. PHYGMOGRAPHS or pulse-writers of

SPHYious kinds have been in use in the medical profession for upwards of ten years. Hitherto they have all been of such monstrous dimensions and of such difficult adjustment on the patient's arm, that their use has been almost exclusively limited to hospital practice. The sphygmograph recently introduced by Dr. Dudgeon, of London, contains all the good points of recommendation-that it is of small size, 24in. by previous sphygmographs, with this additional 2in., very light, 4oz., therefore can easily be carried in the pocket, and capable of being adjusted to the patient's wrist with the utmost case and rapidity. It possesses other advantages over

previous sphygmographs-viz., the pressure of a treadle arranged to act always in one directhe spring on the artery can be altered at will tion. Fig. 1 represents the contrivance in end while the instrument is on the wrist, and it view. Fig. 2, is a side view of the clutch pulley magnifies the movements of the artery in a with one of the plates removed, and Fig. 3 is a definite manner-to wit, 50 times. The com-sectional view of the clutch on the line x x of pactness of the instrument has been obtained by Fig 2. The appliance is shown on a frame in secmaking the several parts of the instrument con- tion in Fig 1, which carries an upper cross-shaft tribute to its stability. Thus, the box that con- A and lower cross-shaft B sustained in suitable tains the clockwork required to propel the smoked bearings. The shaft A is the driven shaft, and paper through the instrument rests upon the carries clutch pulley P and flywheel C. The

and F is

wrist and steadies the machine. In the other treadle shaft B carries a large pulley D,
sphygmographs the clockwork machinery is all smaller pulley E, both of which are fast.
in the air, and requires to be steadied by numerous the treadle hung by one end to the frame of the
straps and arm-rests. One inelastic strap is all machine. From the treadle F a strap passes to
that Dr. Dudgeon's instrument requires, and it and around the pulley E, and from the pulley D
may be used whether the patient is standing, two straps, S T, pass to and around the clutch
sitting, or lying, whereas the other instruments pulley P. These straps S T, are placed side by
require the patient to be in a certain position-side, and are wound in opposite directions, so
generally sitting-in order that it may be used.
The difficulty of applying them, and their large
size, has hitherto prevented the employment of
sphygmographs in ordinary practice; but these
objections are completely done away with in Dr.
Dudgeon's instrument.

that they pass off at opposite sides. The ends of
the straps are connected to the pulleys. The
clutch pulley P is bored centrally for the shaft,
and formed at the sides of the central aperture
with tangential grooves that extend from end to
end of the hub, and open into the bore. In the
grooves are pins or rollers, behind which are
springs that tend to force the rollers towards the
shaft. There are preferably three grooves, and

tion for clutching the shaft A; the shaft is con-
sequently turned, and continues to turn by
momentum of the flywheel during the re-
turn movement of the clutch. This movement
of the clutch by strap T winds the strap S on the
clutch pulley, so that the reverse movement of
the shaft B will unwind strap S, reverse the re-
volution of the clutch, and rewind strap T. The
reversal of the movement is to be accomplished
by a spring or equivalent device. As shown,
there is a spiral spring on shaft B connected to the
frame and to pulley D. At the forward move-
ment the spring is wound, and reverses the
movement of the shaft by its reaction.
be seen that the treadle always turns the treadle
shaft in one direction. The shaft A is turned in
the same direction or the reverse according to
the arrangement of the clutch. The clutch
shown can be used with other forms of treadles,
and the treadle used with a clutch of different
construction. The patentees claim the com-
bination.

It will

the rollers are of such diameter that they M to the front of the dip, and with a saw cut
will jam between the shaft and the tangent sides the cheek down to the depth you require for the
of the grooves.
pulley can turn freely on the shaft in one direc-

With this construction the

turned the reverse way. As shown, the pulley
clutches when turned to the left; but that may

FIG. 2

FICE

臘

Mayo and Perry, of Lowell, Mass. The inven- be changed by simply reversing the pulley on tion is applicable to all machines, such as circular the shaft. In operation, the treadle being saws, lathes, &c., in which high speed with com- pressed down, the strap turns pulley E and shaft paratively small power is required, and consists B, and the strap T being thereby wound on in a "clutch pulley of novel construction" and pulley D, turns the clutch pulley P in the direc

water-lock; then cut the other side, and finally across the top. Prepare a piece of stout lead K, just wide enough to drop into this cut, and burn it there, or, with a copper bit, solder a good thick seam all round the cheeks and top; or, prepared so that it will stand out an inch all should you prefer to wipe it in, let the plate be round.

The object for making this style of trap, • From the Building News. All rights reserved.

is to obtain the width across the dip, which as shown at F. Be careful not to have any allows anything to pass from the inlet side to sharp angles, and that the trap is not wider the body of the trap.

with a stop or solid end, and taking the soil- sometimes do away with the dip, and the trap pipe right down as at J, Fig. 90. Make the is doubtlessly useful in many places where the joint Fon the bottom of the band (which should ordinary trap cannot be used-viz., for be straight at this point), wipe round the check, illustration sake under the bottom of a cistern,

and so on. Now, this mode of connection is very
important, for it will at once be seen that since
the actor is not at the same distance from each
microphone, we hear him differently in each ear,
and just as by our two eyes we have binocular
vision and can judge of distances by sight, so
by our two ears we have binauricular audition, and
can judge of distances by hearing. We can con-
sider this part of M. Ader's invention as a sort
of "stereoscope" for the ear. Thus, at the
Palais d'Industrie, not only we can perceive

sounds, distinguish every voice and every note
of each instrument, but we can also perceive
distances; and although we do not see the actor,
we can hear him move. The microphones on
the stage of the opera are supported on india-
rubber pillars, fixed to a block of lead in order
that the shaking of the floor, when dancing is
going on, may not interfere with the sounds to
be transmitted. On referring to Fig. 1 it will be
seen that the battery Bis short-circuited, and is,
of course, liable to soon get polarised. In order
to avoid this there are four series of batteries
which, by means of commutators, are alternately
put into circuit. This part of the exhibition is a
very great success, both from a popular and
scientific point of view, and there are always
hundreds of persons waiting at the doors of the
telephone rooms in order to hear the opera for
the short space of two minutes.

THE

C. Detaille.

SCIENTIFIC PRINCIPLES
INVOLVED IN ELECTRIC LIGHT-
ING.-VIII.*

By Professor W. GRYLLS, ADAMS, F.R.S.
(Concluded from p. 86.)

The Werdermann or Joel Electric Light.

In the, thread point

the Werdermann system or the Reyner sys

electric light of 6,000-candle power, the cost would be 5d. per hour. If the same illumination be produced by 15 lights of 400 candles each, the cost would be 2s. 1d., or five times as much. Hence the cost for a 400-candle light would be at the rate of about 13d. per hour.

the price of the electric light when obtained by
Now, by comparison, we may get some idea of

means of the Werdermann or Joel lamp. If we
compare the light obtained by the Joel or
Werdermann lamp with that from the 400-candle
light from
the arc, we get about 320-

or, say, 300-candle power in the Joel light
for 800-candle power in the other. Hence the price
of the electric light from the Joel lamp should be
at the rate of 6d. per hour for a 600-candle
power light.

Now, according to Mr. Alex. Siemens' estimate for gas, the price of gas would be at the rate of about 5d.-or nearly 6d.-per hour for the same light. In other words, the cost of the electric light from the Joel lamp would be nearly the same as gas at the rate of 48. per 1,000 cubic feet.

In estimating the candle-power of lamps, it is usual to place the photometer on the same level with the lamp, so that the surface is illuminated by the rays proceeding horizontally from the lamp. Now, in all lamps, whether Werdermann or are lights, which are fed by a continuous-current machine, the current passes from the positive carbon to the negative always in the same direc tion; and in the arc lights, the upper positive carbon becomes worn away into a hollow; hence a portion of this carbon obstructs the light, and the greatest intensity of light is not in a horizontal direction, but downwards, at an angle of about 60° below the horizontal. The illumination in this direction is about three times-or even more than three times-the illumination in the same horizontal plane with the arc; hence, when it is said in the report of the Glasgow tests that a dynamos machine, at 1,200 revolutions per minute, will give a light of 2,060 candles, for an expenditure of 4 h.p.-the light being measured horizontally-we see that the illumination, in a direction inclined downwards at an angle of 60% below the horizon, would be 6,500 candles for 4 h.p., or at least 1,625 candles per h.p. This will also explain why lights fed from continuous-current machines. should be placed at a considerable height above the area to be illuminated. This, combined with the fact that it is far more economical to produce one very powerful light by means of a large machine than several smaller lights to illuminate the same area to the same degree, will explain why Dr. Siemens erected his large lamps at so great a height for the trials of electric lights which we have an opportunity of seeing in the City.

Sub-division of the Electric Current. The next point to which I propose to draw your attention this evening is the sub-division of the electric current.

It will be simplest to regard first the case where this case, according to Ohm's law, there is a battery of given electromotive force. In

E = C (R+ r),

where E is the electromotive force, C the current, R the resistance of the battery, and r the external resistance. If the poles of the battery be joined by two separate resistances r1 and re,

then EC(R+

against a plate or edge of carbon or of copper, and
becomes heated by the current so as to give out a
glowing light, and gradually consumes away, but
more and more slowly as the carbons are more and
more improved. In these lamps, kindly lent to
me by Mr. Latimer Clark, and in these Joel lamps
kindly lent me by Mr. Joel, who has introduced
several improvements into the original Werder
mann lamp, the resistance of the contact of carbon
is very small, about 134 of an ohm; hence it will
take several of them-7 or 8 (or perhaps 10) If the resistance of each branch is equal to r, and
resistance of the electric arc. To work these lamps
arranged in series in the same circuit, to equal the if C1 be the current in each,
of low resistance, only a low electromotive force
is required, and so the result is attained

the internal resistance of the

(

then E = C (R + r) = 2 C, (R+ 5).

then 100 C (1 + 100) = 101 C,
and 100 2 Ci (1 + 50) = 102 C1.
Hence, nearly the same current flows in each
branch as when there is only one wire. If there
are 10 branches instead of two branches, and if C
be the current in each,

then 100 C (1+10) = 110 Cy
100

magnet, of circular form, with two pole-pieces,
around which the bobbins of insulated wire
BB are wound. The particular feature of
this instrument is a soft-iron ring, XX, which by driving a small-resistance dynamo-electric Let E = 100 volts, R = 1 ohm, and r = 100 ohms,
is placed in front of the vibrating-plate, and machine at moderately low speed, or by
which is found to intensify the sounds received. placing a considerable number of lamps in series,
These are the receiving-instruments generally so as to make their combined resistance equal to or
used in Paris, and which have also been adopted greater than
for the Opéra. In Fig. 3 are shown the con-
nections between the Opéra and the Exhibition
P is the prompter's box, on each side of which
are the transmitting-microphones M. There
are ten of them, each connected with a series of
eight telephones. There are ten series, placed
in four rooms, at the Exhibition. I have shown
the connections of one series of eight tele-
phones. Each person has two telephones, one
for each ear.
Now, on examining Fig. 3,
it will be seen that each left-hand tele-
phone is connected with microphone No. 1,
whereas each right-hand telephone is connected
with microphone No. 6. I have not shown the
connections of the other series, but it will easily
be understood that the left-ear telephones of
the second series will be connected with micro-
phone No. 2, and the right-ear ones with No. 7, before the Society of Arts.

machine. Thus a Gramme machine, revolving at
the rate of 1,200 revolutions a minute, giving an
electromotive force of about 130 volts, will give
a current of 50 webers through about 10 lamps
in series. But this current gives an illumination
of 320 candles in each lamp, so that with this i.c., the current in each branch is instead
170
current we get an illumination of 3,200 100
candles in 10 lights. Now, the energy expended 102 If there are 50 branches, and C, be the
to produce this rate of revolution in a Gramme current in each,
machine, is about 9 or 10 h.p. Hence the
Werdermann or the Joel lamp gives at least two
lights of 160 candles each for each h.p. of energy
expended.

Mr. Alex. Siemens lays down in his paper on "Electric Lighting" that 4lb. of coal, costing 15s. a ton, will produce 1 h.p. of energy per hour, and that, if a steam-engine be employed to produce an

* A series of "Cantor Lectures" delivered this

year

=

then 100 C, (1 + 2) = 150 Cg, thus the current in each is 100

150

or 1, and the heating or glowing effect is 4-9ths of its valus with only one branch.

Now, if with 50 branches in multiple are. diminish the external resistance of each branch as to get the same current as at first thenugh each branch,