THERMOMETER AND PYROMETER. 



29 



w. 



Red heat in full day-light ............ o u 



Enamel heat ..... " . ............... 6 



Brass melts. ......................... 21 



Swedish copper melts ................ 27 



Fine silver melts .......... .. ........ 2tt 



Settling heat of flint glass- .......... 29 



Fine gold melts ...................... 32 



Delft ware baked .................... 41 



Working heat of plate glass .......... 57 



Flint glass furnace, low heat ........ 70 



Cream coloured ware baked .......... 86 



Welding heat of iron, least ........ 90 



Ditto ditto greatest ........ 95 



Stone ware, baked ................. U>'J 



Derby China vitrefies ................ 112 



Flint glass furnace, high heat ........ 114 



Inferior Chinese porcelain softened ---- 120 



Bow porcelain vitrified .............. 121 



Plate glass furnace, greatest heat ____ 124 



Smith's forge, greatest heat .......... 125 



Cast iron begins to melt .............. 130 



Bristol porcelain vitrifies ............ 135 



Hessian crucible melted .............. 150 



Cast iron thoroughly melted .......... 150 



Chinese porcelain, best sort softened . . 156 

 Greatest heat of an air furnace eight 

 inches in diameter; deduct soften 

 Nankeen porcelain at all .......... 160 



Extremity of Wedgwood's scale ...... 240 



F. 



K>77 

 1K57 

 3!!n/ 

 4~>:\7 

 471? 

 4847 

 5237 

 6407 

 84H7 

 10,177 

 12,257 

 12,7/7 

 13,427 

 14,3:17 

 15,637 

 1. 1,897 

 16,677 

 16,807 

 17,197 

 17,327 

 17,9/7 

 18.627 

 20,577 

 20,577 

 21,557 



21 ,877 

 32,277 



These results are rendered doubt- 

 ful by the causes already noticed; 

 and the experiments of Morveau and 

 Daniell with pyrometers of platina lead 

 to very different results. 



14. The metallic thermometer of 

 Regnier is described in a report of the 

 French Institute for 1 798.* The inven- 

 tor had remarked, that when a thin 

 metallic rule, resting on a table, is raised 

 by the middle, it forms a segmental arc 

 of which the versed sine, that is a line 

 perpendicular to the chord, drawn to the 

 centre of the arc, is twelve times longer 

 than the space through which the extre- 

 mity of the bar has moved ; and, on this 

 principle, he proposed to construct an 

 instrument for noting variations of atmo- 

 spheric temperature. The small models 

 which he exhibited answered perfectly ; 

 but his intention was, to apply his 

 invention to instruments on a larger 

 scale for public use. 



The instrument consists of two plates 

 of yellow copper, two metres long, fixed 

 in an iron frame, in a bent position, 

 with their concave surfaces toward 

 each other, as in the sketch, fig. 20. 

 On one is fixed a pinion of eight leaves, 

 on an axis, the end of which supports 

 an index to mark the temperature. To 

 the centre of the other plate is attached 

 a toothed rack, in the position of the 

 versed sine of the curve, playing in the 

 leaves of the pinion. When the plates 

 are cooled they approach each other, 

 when heated their centres recede; and the 

 only circumstances of consequence in 

 the position of the bars or plates are, 



* Mtfmoiresde 1'Institut. Nationale, torn. ii. an. ?. 



that they should be at some little distance 

 Fig. 20. 



from each other, and so bent that they 

 cannot become parallel by any reduction 

 of temperature to which they may be 

 exposed. Regnier found, that two such 

 bars, of two metres in length, by a 

 change of temperature equal to 60 cen- 

 tesimal degrees, changed the relative 

 position of their centres, or had a play 

 equal to 65 millimetres ; but the cor- 

 rection for the expansion of the iron 

 frame reduces this by -? 5 ; so that there 

 remains about 26 millimetres for the 

 real play of the centres of the bars ; 

 and if the frames, in public instruments 

 of this sort, are made of stone, that 

 change, by diminishing the expansi- 

 bility" of the frame, will increase that of 

 the bars. Regnier gave a radius of 659 

 millimetres to his index ; so that it 

 will traverse over a circle of 1.299 me- 

 tres in diameter. The pinion has 8 

 leaves in a diameter of 27 millimetres ; 

 and these proportions are such, that a 

 temperature of 60 degrees centesimal 

 will nearly cause a whole revolution of 

 the index round a dial 4.085 metres in 

 circumference. Hence each degree 

 would be about 68 millimetres in size, 

 or rather more than 2 inches ; and 

 consequently might be distinctly seen at 

 some distance. 



15. The platina pyrometer of Guyton 

 de Morveau, /. 21, was laid before the 

 French Institute in 1804, and was de- 

 signed to measure the heat of open fire- 

 places and of furnaces. 



Its basis is a small, yet solid plate 

 , b of highly baked porcelain, in which 

 is a grove capable of containing a flat 

 bar of platina c, 1.75 inch in length, 

 0.2 of an inch broad, and about 0.1 of 

 an inch in thickness. One end of this 



