Mr. Daiiiell on a nexo Register-Pyrometer. 

 Planes al, a2, «3, cl, c2, ^1, ^2, ^3, f\,f% 



5 3 13 



Symbols O, O, O, A, 



1 

 A, 



3 



E, 



191 



h. 



2 11 * d 1 



E, E, D, D, B, H. 



= 159° 30' 

 = 150 23 

 = 129 42 

 = 110 12 

 = 132 55 

 PJ^2 = 120 42 

 P,M = 104 48 



P,al 

 P,a2 

 P,a3 

 P,A 



P,„ 



P,el = 



P,e2 = 



V,eS = 



P,.- = 



M,M' = 



86 



145 7 



133 43 



115 33 



93 52 



95 38 



Some of the crystals are hemitrope, the plane of revolution 

 being parallel to the terminal plane. 



XXV. On a nex<o Register-Pyrometer, Jar Measuring the 

 Expansions of Solids, and determining the higher Degrees 

 of Temperature upon the common Thermometric Scale. By 

 J. Frederic Daniell, Esq. F.R.S.* 

 [With a Plate.] 



IN the year 1821 I published in the Journal of the Royal 

 Institution! an account of a new pyrometer, and the re- 

 sults of some experiments with it, which were the means ot 

 correcting the highly erroneous notions which had, up to that 

 time, been generally entertained of the degrees of temperature 

 beyond the boiling point of mercury. The mstrument was 

 capable of affording correct determinations, connected in an 

 unexceptionable manner with the scale of the mercurial ther- 

 mometer; but, although applicable to scientific investigation 

 in careful hands, it could be inserted only into experimenta 

 furnaces of a particular construction, which greatly limited 

 its use. The great desideratum still remained of a pyrometer, 

 which might universally be applied to llie higher degrees o 

 heat, as the thermometer has long been to the lower ; ami 

 which, in addition to its use in delicate researches, might ellcct 

 for tiie potter, the smelter, the cnameler and others, in the 



• From ti.e Philosoijhical Transactions for 1h:?0: Part II., and revised 

 Ijv the Author. t Vol. xi. [>. 309. 



' routme 



