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XX. On a new Register-Pyrometer, for 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. 
Read June 17, 1830. 
In the year 1821 I published in the Journal of the Royal Institution* an ac- 
count of a new pyrometer, and the results of some experiments with it, which 
were the means of 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 instrument was capable of affording correct 
determinations, connected in an unexceptionable manner with the scale of 
the mercurial thermometer ; but, although applicable to scientific investiga- 
tion in careful hands, it could be inserted only into experimental furnaces of a 
particular construction, which greatly limited its use. The great desideratum 
still remained of a pyrometer, which might universally be applied to the higher 
degrees of heat, as the thermometer has long been to the lower ; and which, in 
addition to its use in delicate researches, might effect for the potter, the smelter, 
the enameler and others, in the routine of their business, what the latter daily 
performs for the brewer, the distiller, the sugar-refiner, and the chemist. 
I shall now have the honour of laying before the Royal Society a description 
of a contrivance which, I trust, will be found to answer all the desired purposes; 
and which, while simple enough to be intrusted to the hands of common work- 
men in every variety of fire-place, I hope to prove, by the results of my experi- 
ments, to be sufficiently delicate to extend considerably our knowledge of the 
expansion of metals, upon which so much labour has been bestowed by some 
of the first philosophers. 
I was not aware, at the time when I wrote the account above referred to, that 
the subject had been previously investigated by M. Guyton de Morveau, and 
that he had proposed to apply the expansion of platinum as a measure of high 
* Vol. xi. p. 309. 
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