THERMOMETER AND PYROMETER. 



31 



sion of the zinc c d will bend the whole 

 bar, as in the figure ; and the index g 

 will move along the graduated arc, 

 from right to left, in proportion to the 

 temperature. In order to convert it 

 into a register thermometer, Crighton 

 applied two slender hands h, h on the 

 axis of the index: these lie below the 

 index, and are pushed in opposite direc- 

 tions by the stud /, a contrivance seem- 

 ingly borrowed from the instrument of 

 Fitzgerald. 



On the whole, the principle of this 

 pyrometer is just ; but it does not seem 

 to possess any considerable advantages 

 over several of those already noticed. 



17. We have some doubts of the 

 propriety of noticing a sort of air py- 

 rometer, fig. 23, proposed by M. Schmidt 



of Jasy in Moldavia.* It is so evi- 

 dently a mere theoretic proposal, and is, 

 besides, an expensive, clumsy, and pro- 

 bably not very accurate mode of ascer- 

 taining high temperatures. It consists 



of a bottle a, and narrow tube b of pla- 

 tina, the former to receive the impres- 

 sion of the heat, and the latter to convey 

 the expanded air into c c, an air-tight 

 cistern partially filled with water. The 

 cover of the cistern is perforated by 

 three holes ; in one of which the end of 

 the platina tube is cemented ; in the 

 second is fixed a glass tube d, contain- 

 ing a common thermometer ; and in 

 the third, a slender graduated tube e, 

 which dips into the water in the cistern. 

 The thermometer is for ascertaining 

 the temperature of the included air of 

 the cistern before the experiment ; the 

 graduated tube for ascertaining the 

 temperature communicated to the pla- 

 tina bottle by the ascent of this water 

 raised by the pressure of the expanded 

 air on the surface of the fluid in the 

 cistern. Any further description would 

 be superfluous. 



The pyrometer of Mr. Daniell (Jig. 

 24) was first described in Brande's 

 Quarterly Journal* The moving power 

 is a rod or wire of platina 1 0.2 inches 

 in length, and 0.14 inch in diameter, 

 fixed in a tube of blac;klead ware a, b, c, 

 by a flanch within and a nut and 

 screw without the tube at a. This tube 

 has a shoulder moulded on it at b, for 

 the convenience of always inserting it 

 into the furnace, or muffle, to the same 

 depth. From the extremity of the pla- 



Fig. 24. 



.A 



tina rod at b proceeds a fine wire of 

 the same metal, ^ inch in diameter, 

 which comes out of a brass ferrule d, 

 and passes two or three times round 

 the axis of the wheel t, B, Jig. 24. It 

 then bends back, and is attached to a 

 slender spring m n, which is fixed by 

 one end to the pin at ?i, on the outside 

 of the ferrule. 

 The substitution of a silk string for 



Nicholson's Journal, 8vo, series, vol. ii. 141. 



that part of the platina wire lapped 

 round the wheel, and connecting it with 

 the spring, has rendered the motions of 

 the index more sensible. The axis of 

 i is = 0.062 inch, and the diameter of 

 the wheel one inch : its teeth play in 

 the teeth of another wheel just one- 

 third of its diameter, by which the 

 wheel k has three times the movement 

 of i ; and the index on the axis of k 



JVol. xi.p.309. 



