« ElőzőTovább »
this ftar, and of the opinions of the the London Magazine for last May. astronomers in different parts of Europe, The eulogium is well merited by such was presented to our readers, in the eminent abilities. Those who enjoyed Aftronomical department of our last the pleasure of attending Mr. Barry's Magazine.
exhibition will acknowledge the truth To this poem Mr. Tasker has sub- of the praise, and thank Mr. Tasker, joined a copy of verses to Dr. Johnson, for recalling to their memory a work of which the thoughts are sometimes which displayed so uncommon an exvigorous, and the lines generally mu- ertion of the human powers, and so fical. The line on Mr. Barry, the won rfal an union of splendid tapainter, which follow, were published in lents and indefatigable induitry:
ART. XIX. The Doctrine of Ecliples, both folar and lurar; containing there and inly Precepts for computing jolar and lunar Eclipses. The general and geographical Phenomena of Polar Eclipses. The Phenomena of jolar Eclipses for any particular Place, with or without Parallaxer, fully and clearly explained, from the latest Discoveries and Improvements; whereby any person of a moderate Capacity may be able in a fiart Time to Jol-ve thefe grand and fublime aftronomical Problems. With correct astronomical Tables from a manufcript Copy of the Tabrile Dunelmenfes, fiited to the Meridian of Greenwich. By Blich Hancock, Teacher of the Mathematics. 8vo. Booth at Norwich.
THE contents of this pamphlet are are not so convenient for use. The set forth in the title-page to fully, that merits of the Tabulæ Dunelmenses are now it is unnecessary for us to add a word well-known to everyone who is converon the subject. With respect to the fant in these speculations though toleraexecution, we have only to fay that bly exact, confidering the number of there are reasons for thinking the au- equations that are employed, they are thor knows what he is about; but, un very inferior, in that respect, to the fortunately, he expreffes his meaning tables of Mayer and Morris. 1o badly, that we fear no other person We cannot conclude this short arwill, who is not, at least, as well ac ticle, without expressing our astonishquainted with the subject as himself. ment that the name of Dr. Parr, of
The tables are not the Tabula Di- Norwich, who, in depth of learning and uclmenfes, but acompilation from them; elegance of taste, has fo few rivals, which, for any thing that we know to should be found at the head of the the contrary, may be as exact, but they dedication prefixed to this performance.
Arr. XX. Philosophical Transaélions of the Royal Society of London, Vol. LXXII. for the lear 1782, Part II. London. Davis and Elmiley.
THIS volume contains ten papers, in this memorial. He begins with obof which some are on very curious serving, that “ a measure for the highsubjects. We shall give an account of er degrees of heat, such as the comtheir contents, in the order which has mon thermometers afford for the lower been assigned them, in this second part ones, must be an important acquisition, of the Philosophical Transactions for both to the philosopher and the practithe year 1782.
cal artist." I. An atteinpt to make a thermome As there are many experiments, in ter for measuring the higher degrees which the precise measure of heat emof heat, from a red heat up to the ployed has never been ascertained, Itrongest that veffels made of clay can such an instrument will be of fingular fupport. By Jofiah Wedgwood. Com- use. Many processes will be rendered anunicated by Sir J.Banks, Bart. P.R.S. easy, and their success certain, which
(Read May 9, 1782.) have frequently failed, owing to the Mr. Wedgwood, formerly the part- difficulty of seizing the moment when ner, and now the fucceffor, of the late there was neither an excess of heat, Mr. Bentley, displays uncommon in nor a deficiency. genuity and very extensive knowledge Mr, Wedgwood tells us, that he has
frequently been perplexed, in the ex the different shades of colour. This periments which he has made for the diminution begins in low red heat, and improvement of his manufacture, to proceeds, as the heat increases, till the ascertain the exact degree of heat to clay is vitrified. The contraction of which his experiment pieces were ex fome good clays is confiderably more posed. Red, bright red, and zohite heat, than one fourth part in every dimension. are indeterminate espressions; and on He then proposes to get a " meathe measures which the kilns afforded sure of fire fufficient for erery purpose he could not always place dependance. of experiment or bufiness, by con
The effects of fire upon some known triving to measure the contraction of body can alone ascertain its force. It clays, unvitrescible, and alwave equal is well known that it changes colours, ly contracted by heat, with ease and and he observed that compositions of minute accuracy." calces of iron with clav aisumed such The best clay for supporting the indistinct colours and shades, as pro- tensity, and measuring the degrees of mised to afford useful criteria of the fire, he found to be the purest Cornish respective degrees.
porcelain clay, which he prepared in He, therefore, prepared feveral cir- the following manner: cular pieces of such a composition, When the clay is washed over and about an inch in diameter, and a quarter passed through a lawn, of which the of an inch thick. These were placed interftices Mould be less than the in a kiln heated as uniformly as polii- 100,000 part of an inch, it must be dried, ble for fixty hours.
and put into boxes, to prevent, the At equal intervals these pieces were effects of air and moisture. taken out, and piled, in a glass tube, “ The dry clay is to be softened upon one another, and exhibited rather for use, with about two fifths of its an extenfive series of colours; from a weight of water; and formed into flesh colour to a decp brownish red, small pieces, in little moulds of metal, thence to a chocolate, and so on to fix-tenths of an inch in breadth, with nearly black, with all the intermediate the sides pretty exactly parallel, this tints.
being the dimenfion intended to be To this tube a back was fixed, and measured, about four-tenths of an inch the numbers of the pieces marked upon deep, and one inch long. To make it respectively oppolite to them, like the clay deliver easily, it will be necesthe scale of a thermometer. These fary to oil the mould, and make it numbers resemble thermometric divi. sions or degrees; so that if another “ Thefe pieces, when perfe&tly dry, picce of the fame composition were are put into another iron mould or heated in any other kiln, not exceed- gage, confifting only of a bottom, ing the utmost heat of the first, it with two sides, five-tenths of an inch would acquire a colour corresponding deep; to the dimensions of which fides to some of the pieces in the tube, and the breadth of the pieces is to be pared point out the degree of heat which that down. piece has undergone.
“For measuring the diminution A thermometer on such a principle, which they are to suffer from the action Mr. Wedgwood allows is liable to ob- of fire, another gage is made of two jections. Ideas of colours cannot be pieces of brass, twenty-four inches communicated by words. The various long, with the sides exactly straight, shades cannot be equally distinguished divided into inches and tenths, fixed by all eyes, nor by all lights, and may five-tenths of an inch asunder at one be altered by phlogistic vapours.
end, and threc-tenths at the other, The diminution of argillaceous bo- upon a brass plate; so that one of the dies by fire, Mr. Wedgwood observes, thermometric pieces, when pared down is a distinguishing character of this or- in the iron gage, will jutt fit to the der of earths, and is a more accurate wider end. Let us suppose this piece and extensive measure of heat than to have diminished in the fire one-fift!
of its bulk, it will then pass on to into intense fire, and, when they have half the length of the gage; if dini- received its heat, may be plunged as nished two-fifths, it will go on to the suddenly into cold water, without the narroweit end; and in any interme- least injury from either. diate degree of contraction, if the piece “ Even whilst saturated with water be flid along till it rest against the in their porous flate, they may be thrown converging fides, the degree at which immediately into a white heat, withit stops will be the measure of its con out bursting or fuffering any injury. traction, and consequently of the de Sudden cooling, which alters both gree of heat it has undergone." the bulk and texture of most bodies,
These are the outlines which Mr. does not all affect there, at leatt not Wedgwood gives, as neceflary for in any quality subfervient to their thermaking and uting this thermometer. mometric uses. He then tells us, that there are inex “ Nor are they affected by long conhaustible mines of this clay in Corn- tinuance in, but folely by the degree wall; and adds that all the clay em- of heat they are exposed to. In three ployed in these thermometers should minutes, or less, they are perfectly pebe perfectly similar.
netrated by the heat which acts upon The qualities of this clay are very them, so as to receive effeci) the full accurately described, and rules are laid contraction which that degree of heat down, that all thermometers which is capable of producing, equally with are made on this principle may be those which had undergone its action equally altected by heat, though made during a gradual increate of its force in different parts of the world, and by for many hours. Strong degrees of different persons.
heat are communicated to them with Rules are then given for the forma more celerity than weak ones: perhaps, tion of a scale. Mr. Wedgwood at the heat may be more readily transone time hoped that the gradation of mitted, in proportion as the texture bethe common thermometer might be comes more compact.” continued up to the red heat, at which After relating the qualities of these the shrinking of the clay commences, thermometer pieces, Mr. Wedgwood so as to connect the two thermometers proceeds thus: together by one series of numbers; « The use and accuracy of this therbut he found that the loss of weight mometer for measuring after an operawas not suficiently uniform, or pro- tion the degree of heat which the portional to the degree of heat, to an matter has undergone, will be apparent; Iwer that purpose. Mr. Wedgwood the foregoing properties afford means relates the following fingular properties of mcafuring it, also, easily andexpediof these thermomiters, which rensler tiously during the operation, so that them peculiarly fit for the purposes to we may know when the fire is encreased which they are applied.
to any degree previously determined “ When baked by only moderate upon. The piece may be taken out of degrees of fire, though they are, like the fire in any period of the process, other clays, of a porous texture, and and dropped immediately into water; imbibe water, yct, when faturated with so as to be fit for measuring by the the water, their bulk continues exactly gage in a few seconds of time. At the same as in a dry state.
the same inftant, another piece may * By rery streng fire they are chianged introduced into the place of the former, to a porcelain of femi-vitreous texture; to be taken out and measured in its nevertheless their contraction, on fur- turn; and thus alternately, till the dether augmentations of the heat, pro- fired degree of beat is obtained. coeds regularly as before, up to the as the cold piece will be two or three highest degree of fire that I have been minutes in receiving the full heat, and able to produce.
corresponding contraction; to avoid “ They bear sudden alternatives of this loss of time, it may be proper, on heat and cold; may be dropped at once fome occasions, to have two or more
pieces, according to convenience, put The Roman
about 360 in together at first, that they may be Worcester china vitrified at fuccedively cooled in water, and the Chelsea china at
105 degrees of heat examined at shorter in- The Derby at
Bow at Mr. Wedgwood's scale commences Bristol china shews no vitrification at at red heat, fully visible at day-light,
135 and the greatest heat which he has been But the common Chinese porcelain he able to obtain is 160 degrees, which could not vitrify. It became soft at was produced in an air furnace about 120°, and funk down, and applied iteight inches fquare.
self close to the irregularities of the Various experiments have been made surface underneath, at 1569. He could with this new thermometer, to ascer- not foften the true stone Nankeen, nor tain the degree at which pure metals the Dresden porcelain. go into fusion. It has been found, that Mr. Pott says, that it is “ among
Swedish copper melts at 270 the master-pieces of art” to melt a
23 mixture of chalk and clay in certain Gold
proportions, which from his tables apBrass *
pear to be equal parts. Mr. WedgIt has been likewise discovered, that wood found that this mixture melted he welding heat of iron is from go to 95 into a perfect glafs at The smith's forge can be heated only to All experiments may have their re
125 fpective degrees of heat ascertained by Calt iron melted at
130 repeating and accompanying them with Iron is run down among the fuel at 150 these thermometric pieces. By these Copper melted at
27 means they may be rendered more in- On examining glass furnaces, in one telligible and useful to the reader, the the perfect vitrifcation of
experimenter, and the working arFlint glass was
1140 tili. In another only
70 By this ingenious discovery Mr. Plate glass
,124 Wedgwood has opened a field for therDellt ware is fired at
40 or 41 mometrical inquiries, which has never Queen's ware at
86 been explored. He has enabled manStone ware, or Pots du Grès, at 102 kind to judge with more clearness and
These thermometers have enabled the precision about the differences of the ingenious inventor to ascertain the degrees of strong fire, and their corheats by which many of the porcelains responding effects upon natural and arand earthen wares of distant nations tificial bodies. These degrees may and different ages have been fired. now be accurately measured, and comCompositions in which clay is the pared with each other, as well as the principal ingredient suffer no diminu- lower degrees of heat, which are meation in buik, till they are exposed to surable by the common mercurial thera greater heat than they underwent ori- mometer. ginally. Mr. Wedgwood finds, there This paper is followed by an Appenfore, that the ancient Etruscan wares dix, which exhibits an analysis of the appear to have undergene heats from clay with which these thermometric 20° to 32°:
pieces are formed. Mr. Wedgwood Jasper diminishes in fire; granite is concludes from his experiments, that it enlarged; while flint and quartoze is a substance of a liliceous kind, bestones are neither enlarged nor dimi- cause it cannot, from its qualities, beniihed. These experiments were made long to any other order of earthy boin fires betiveen 70 and 80° of this dies. The clay he proves to consist thermometer.
of two parts of pure filiceous earth to Mr. Wedgwood informs us, also, that three parts of pure argillaceous or aulthe Etruscan ware melted at 33° minous earth.
II. An * It is remarkable, that in brass and copper founderies the workmen carry their fires to 140.
II. An Analysis of two Mineral fhire. It is of a dark brownish gres, Substances, viz. The Rowley Rag a granulated texture, with several caStone, and the Toad Stone. By Wil- vities filled with crystallized spar. It liam Withering, M. D. Communi- does not strike fire with steel, and irelts cated by Joseph Priestley, LL. D. to a black glass. F. R. S. to Sir J. Banks, Bart.P. R. S. We must omit the experiments,
Dr. Withering's accuracy in pro- which are very curious. From them, cesses of the kind is well known; and the Doctor proves that 100 parts of the sanction given by the name of this specimen of toad-stone contained Priestley, who communicated this pa Siliceous earth
6316 per to the President, cannot but con Calciform iron
16 firm his former reputation.
Calcareous earth Dr. Withering's analysis of the dif Earth of allum
14 ferent marles found in Staffordshire was published, in the Philofophical Tranfactions, some years ago. *This exami From the addition of 1-5. of weight, nation of these two minerals are to be it is probable, that the substances ca considered as part of a chemical ana- pable of uniting with fixable air, were lysis of all the substances which exist not in the specimen used fully faturated in the earth, in large quantities. with it, as they would be after their
The Rowley Rag Stone forms a chain precipitation by the mild alkaly. of hills in the southern parts of Staf Dr. Withering has subjoined to this fordshire. The lime itone rocks of paper, a table to thew the folubility or Dudley bed against them. The highet insolubility of several saline subkances part of them is near the village of in Alcohol. Rowley. This stone is found likewise III. New Fundamental Experiments at some distance from the hills, and al- upon the Collision of Bodies. By Mr. ways appears in rhomboidal pieces. It John Smeaton, F. R. S. in a Letter to has lately been employed in paving the Sir Joseph Banks, Bart. P. R. S. streets of Birmingham, and has been (Read April 18th 1782.) sold in powder, as a substitute for eme It is universally acknowledged that ry, in cutting and polithing.
the first principles of science, and more Its appearance is a dark grey, with especially of those sciences which imnumerous minute thining chryfials. It mediately relate to the practical parts strikes fire with steel, cuts glass, melts of mechanics, cannot be examined with under the blow-pipe, and becomes too much minuteness: the public is, magnetic when heated in an open fire, therefore, greatly obliged to this excel
For the experiments we must refer to lent mechanician for his many ingenious the paper, and content ourselves with enquiries into these interesting branches laying the conclufions before our readers. of science. His firit paper, containing an
The proportions in a 100 parts of account of his experimental enquiries this stone were found to be these: into the natural powers of wind and waPure filiceous earth
ter to turn mills and other large maPure clay, free from fixable air 321 chines, was published in the PhilofophiIron in a calciform state
cal Transactions for 1759, and for it he was honoured with Sir Godfrey Copley's
prize medal for that year: that paper, we From this view of the component believe, was read with universal fatisfac. parts, Dr. Withering concludes that it tion. In the Philosophical Transactions might be used with advantage as a for 1776, his experimental enquiry into fius for calcareous iron orcs, which the the quantity and proportion of me. makers of iron have seldom worked, chanic power necessary to be employed for want of a Aux at once cheap and in giving different degrees of velocity eficacious.
to heavy bodies, from a state of ret, TOAD-STONE.
was published; and the experiments re. The Toad-Stone is found in Derby-lated in that paper, as far as we know,