'211 



PYROMETER. 



Pyrometers 

 fur measur- 

 ing the "ex- 

 pansion of 

 metallic 

 bodies. 

 Miiiichcn- 

 licoek's 

 pyrometer. 

 PLATE 



i < <. I J.XXI. 



No. II. 



Fig. 1. 



P>rotTK'tcr. X HE name Pyrometer, from ri/j, far, and turpi, a 

 '*~T~~' measure, is piveii to those instruments which measure 

 tin- expansion of solid bodies by heat, and to another 

 class (if instruments which measure degrees of heat 

 above those which can IK* indicated by the mercurial 

 thermometer. This last application of the name is by 

 no means judicious, and, consequently, pyrometers of 

 this kind hhould be considered as thermometers. We 

 shall, however, proceed to describe these instruments 

 in the order of their invention, and under the two 

 different classes now mentioned. 



CHAP. I. ON PYROMETERS FOR MEASURING TUB 

 EXPANSION OF METALLIC BODIES. 



I. Muschcnbrock's Pyrometer. 



Tins machine, which we shall describe nearly in the 

 words of the original inventor, is represented in Plate 

 CCCCLXXI. Xo II. Fjg. 1, where AAA is a piece 

 of iron turned up perpendicularly at one end, the re- 

 turn being 1 T R _ inch high. The other end, distant from 

 it J inch is aUo turned up, and is turned back again, 

 bo as to make a broad square plate, the side of which 

 is 2 inches. The iron itself is 1 inch wide and ^ thick. 

 Upon the iron plate stands a brass machine, which 

 Fig. ?. i drawn by itself in Fig. 2, where it is represented 

 larger, and seen from another side, th& better to 

 discover its parts, which are marked with the same 

 letters as in Fisr. l. This is fixed to the iron by two 

 screws X, X, which are its legs. D is a circular plate 

 of 2 T l r, inches diameter, divided into 300 equal parts. 

 This divided plate stands upon four pillars E, E, E, E, 

 which join it to the lower brass plate ; between these 

 two plates there is a perpendicular steel axis F, which 

 has on its lower part a pinion of 6 leaves, and on its 

 upper a wheel of 60. teeth marked G : There is also 

 another axis I H, supported by a cock from the upper 

 plute, and which axis receives the index I K ; having 

 at its lower end a pinion of 6 leaves to. take the teeth 

 of the wheel G. The index, by one turn of the pinion 

 H, is carried round to all the divisions. There is be- 

 sides, a little rack L with teeth, which take the leaves 

 of the pinion F, while the rack slides along under two 

 small cocks P, P, where it is pressed towards the pinion 

 F by two small screws M, M, or drawn from it as 

 there is occasion, that the teeth may neither stick nor 

 be loose. - The teeth of the rack are 25 in an inch, and 

 as it moves forward and backward, the pinion F is car- 

 ried round, and consequently the wheel G, which car- 

 ries round the pinion H, together with the index I K. 

 Let the rack have run one inch ; then F and G will 

 have turned round 4 times and ; and consequently the 

 pinion H will have gone round 10 x 4^, that is, 41y 

 times. Hence 41| x~ 300 = 12,500 parts. Therefore 

 one division corresponds to the 12500th part of an inch. 

 Fig. 3. Fig- S- represents a square bar, or parallele- 



piped of metal, upon which the experiment is made, 

 5,^0 inches long, and ^ of an inch thick. One end of 

 it O has a small tail, that it may communicate no sen- 

 sible degree of heat to the iron A A ; it is received in 

 a notch near B, and fixed by the screw C. Its other 

 end X has a hole in it, through which goes the screw 

 Q, which makes it fast to the rack L. 



The bar being thus fixed, cannot become longer, 

 without pushing forward the rack L, and moving 

 round the hand I K ; so* likewise, when it becomes 

 shorter, it must move the contrary way. The weight of 



the bar is support, d by a piece of watch-spring be. 

 tween the nquare iron and bras plates E A. Tu apply 

 conveniently the flame of spirits, there is a box of 

 brass. 3 inches long, 1 -^ inch wide, and -^ inch 

 deep, covered at top with a piece of blue stone, such 

 as will bear the fire. It has a long hole cut through the 

 middle, into which is let in a brass plate T, which has 

 5 small equidistant holes * ff parts of an inch asunder, 

 and T-J--T inch in diameter, to transmit the wicks of the 

 lamp. This lamp has 4 feet, which closely take in the 

 iron A between them, that the flame may come against 

 the middle of the bar; but the bottom of the lamp 

 must not touch the iron. The distance between the 

 bottom of the bar and the upper surface of the lamp, 

 must be half an inch, that the cotton wicks which stand 

 up ,". of an inch may give an equal flame. The cot- 

 ton threads mut be fine and even, and 5 of them 

 must make a wick of about T -j of an inch. If the 

 wick is drawn up too high, the flame will be too large. 

 In experiments with highly rectified spirit of wine, 

 there was always an equal quantity put into the lamp. 

 In the following table, the expansions are marked in 

 parts, of which each is the 17 }--i 7 part of an inch : 



See Muschenbrock's Tentamina Academiae deli Ci- 

 mento 1731, Part ii. p. 12; and Desagulier's Xat. 

 Phil. Vol. i. p. 439. Edit, third. 



2. Desaguliers' Improvement o.i Muschenbrotk't 

 Pyrometer. 



Dr. Desaguliers made several important improve- Desagu. 

 ments on this instrument. In place of square rods '"' -ro- 

 of metal, Dr. Desaguliers used cylindrical ones, B N, P r * PT- 

 Fig 4, as they could be made more uniform, by being Jj" 11 ' 

 drawn like wires. Instead of the pinion F, he used a CCCCLXXU 

 small roller H made of steel, truly tempered, but not po- jjo. II. 

 lished, and filed on its surface in the direction ot its axis, Fig. 4. 

 so that it became a small wheel with an infinite number 

 of teeth. The wheel gg, on the same axis, has no teeth, 

 but has a groove, to receive a fine watch chain, or a 

 horse's hair, which carries round a roller i, having 

 also a small groove. Upon the upper end of the axis 

 of this roller the index k i n is fixed. In order that the 

 chain by which gg carries i may be properly extended, 

 the whole dial plate, and the cock and pinion i, can 

 be moved to or from the wheel gg by a screw fastened 

 to the upper frame plate. Instead of the rack M 



