

PYROMETER. 



IVometer. ther distinl at one end EG than at the other end III, 

 ao as to include a long converging canal, which i.s divided 

 on one Mile into a number of Miiall equal parts. 

 it a body I is so adjusted as to fit exactly at the narrow 

 end Ml of the canal, so that its lower tide stands ex- 

 actly at ; then, if it is expanded by heat, and ap- 

 plied in that expanded htate to the scale, it will no 

 longer fit into the narrow end FH, but will fill a wider 

 part of tin- scale farther up, and the divisions opposite 

 to the lower side of I, when it fits, will indicate tin- de- 

 gree of expansion. In like manner, the degree of 

 contraction will be obtained by the reverse operation. 

 The following Table, given by Mr. Wedgewood, shows 

 the relation between his pyrometer and the thermome- 

 ter of Fahrenheit 



Extremity of the scale of Wedge- 



wood's Pyrometer, 

 Greatest heat of 31 r. Wedgewood's 



great furnace, 

 Cast Iron melts, 

 Greatest heat of a common smith's 



forgo, ... 



\Vclding heat of Iron. Greatest, 



. Least, 



Fine gold melts, 



Fine silver melts, 



Swedish coppev melts, * 



Brass melts, 



Heat with which Mr. Wedgewood's 



enamel colours ure burnt in, 

 Red heat fully visible in day-light, 

 . in the dark, 



Fahrenheit. Wedgewood. 



32,277 



21,877 

 17,977 



17,327 



13,427 



12,777 



6,237 



4,717 



4,o87 



3.B07 



1,857 

 1,077 

 947 

 600 

 212 

 97 

 32 

 



240 



160 

 130 



so 



32 



28 

 87 



Mercury boils, 



Water boils, 



Vital heat, 



Water freezes, 



Proof spirit freezes, 



The point at which mercury congeals, 

 and consequently the limit of mer- 

 curial thermometers, - 40 



See Phil. Trans. 1782, v. Ixxii. p. 305. Id. 

 v. Ixxiv. p. 358 ; and Id. 1786, v. Ixxvi. p. 390. 



6 







1 



3.673 

 6.658 

 7.548 

 8.042 

 8.289 



8.596 

 1784, 



2. Description of Guyton's Platina Pyrometer. 

 Guyton's The object of this instrument, which was exhibited 

 platina py- to tne Xational Institute in 1803, was, to measure the 

 rometcr. n jgh est degree of heat in our furnaces. It consists of 

 A rod or plate of Platina, placed horizontally in a groove 

 formed in a cake of hardened white clay. This plate 

 is supported, at one of its extremities, on that part of 

 the mass which terminates the groove, while the other 

 extremity presses against a bent lever, whose longest 

 arm forms an index to a graduated arch, so that the 

 expansion is indicated on the scale by the inuex. The 

 bar of Platina was an inch and three quarters long, 

 a quarter of an inch wide, and one-thirteenth of an 

 hich thick. The arm of the bent lever, against which 

 the platina bar presses, is one-ninth of an inch ; and 

 the arm, at fight angles to it, which acts on the index, 

 one inch and eight-tenths, or twenty times as long. 

 The index carries a nonius, which divides each degree 

 into ten parts ; hence Guyton calculates that we may 

 measure an expansion of the 5730-th part of the radius. 

 In order to prevent the position of the index from be- 

 ing changed, in removing the instrument from the 

 furnace, a plate of platina is fixed so as to form a spring 

 against its extremity. See the Annalex de Chimic, No. 

 138. vol. xlvi. p. 276, and Nicholson's Philosophical 

 Journal, vol. vi. p. 89. 



3. Description pj' Mr. Daniell't Platina Pyrometer. P/romeur- 



The pyrometer of Mr. Wedgewood, ingenious as it 

 is, had nevertheless fallen into disuse, both from the fj"^ 1 ' . 

 extreme difliculty of procuring pieces of clay of uniform ^^^g^' 

 composition, and from its having been found that 

 time has an influence on the contraction of the clay 

 pieces, the longer continuance of a low degree of 

 heat producing the same contraction as a higher de* 

 gree of heat continued for a shorter time.* 



Mr. Daniell was therefore led to construct a py- 

 rometer free from these defects, and which promises 

 to be of much utility in the arts, as well as in 

 the sciences. It is represented in Plate CCCCLXXI. PIATE 

 Fig. 10 and 11 ; Fig. 10 representing the whole Instru- " 

 ment, and Fig. 1 1 a part of half the real dimensions. "' 

 The tube a b c is made of black lead earthen ware, n/ 

 and the shoulder in its centre is moulded when it is 

 formed. The end a of the tube is close, and the end 

 c, which is open, is accurately fitted into a ferule of 

 brass rf, which carries the scale efgh. Within the 

 tube a b is a bar of platinum 10.2 inches long, and 0.14 

 of an inch in diameter, extending from b to a, where 

 it is fixed by a nut and screw of the same metal on the 

 outside, and a pin or shoulder on the inside. At b it 

 is kept in its place by a small perforated plate of pla- 

 tinum through which it passes. A fine platinum wire 

 about 100th of an inch in diameter, proceeds from the 

 end b of the platinum wire, and coming out of the 

 tube at d, a piece of silk thread attached to it. is coiled 

 twice or thrice round the axis of the wheel i, fixed on 

 the back of the scale, and shown in Fig. 11. The 

 thread is then turned back, and attached to the ex- 

 tremity of a slight spring m n, which is stretched on 

 the outside of a brass ferule, and fixed by a pin at n. 

 By this means the action of the spring keeps the wire 

 in a state of tension. The axis of the wheel is 0.062 

 of an inch in diameter, and the wheel itself, which is 

 toothed, works in the teeth of another smaller wheel 

 /c, one third the diameter of the other, and having o;re 

 third of the number of teeth. An index /is fixed to 

 its axis, which passes through the centre of the scale 

 efg h, which is divided into 360 degrees. 



When the extremity a b of the instrument is put 

 into the fire, the index /.at first moves backwards 10 

 or 20 degrees, in consequence of the expansion of the 

 black lead tube, before the heat has reached the pla- 

 tinum bar ; but in a short time it moves rapidly for- 

 ward, and indicates on the scale the degree of expan- 

 sion experienced by the bar. By various interesting 

 experiments, for which we cannot find room, Mr. Da- 

 niell obtained the following results, which we give, 

 along with those of Mr. Wedgewood. 



Fusing point of cast iron, 

 Fusing point ot gold, 

 Fusing point of copper. 

 Fusing point of pure silver, 

 Fusing point of brass, 

 Heat of a common parlour 



fire, ... 

 Red heat, just visible in day- 

 light, . 



Fusing point of zinc, 

 Mercury boils, . 

 Fusing point of lead, 

 Fusing point of bismuth, 

 Fusing point of tin, 



DANIELL. 



Fahr. Pyrometer. 



3477* 

 2590 

 2548 

 2233 



1141 



980 

 648 

 644 

 609 

 462 

 441 



497 



370 



361 



319 



267 



163 



140 

 94 

 9 

 87 

 66 

 63 



WEDGEWOOD. 



Fahr. Pyrometer. 



17977 

 5237 

 4587 

 4717 

 3807 



1077 



600 



130 

 32 

 27 

 28 

 21 



3.673 



Mr. Sirright has proposed to substitute pieces of Agalmatclite in phici of Widgewood't clay piece*. 



