192 Mr. Daniell 07i a ne-w Register-Pyrometa'^ 



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 experiments, to be sufficiently delicate to extend 

 considerably our knowledge of the expansion of metals, upon 

 vi'hich 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 tempe- 

 rature, and more particularly to the purpose of connecting the 

 indications of Wedgwood's pyrometer with the mercurial 

 scale and verifying its regularity. I have since carefully 

 studied his laborious papers in the Annates de Chimie*, and 

 the Memoires de Vl7istitut\, which appear to have been but 

 very little known in this country ; and previously to entering 

 upon the moi-e particular object of the present paper, I must 

 claim indulgence for a few remarks upon the general state of 

 the inquiry at the time when its pursuit was abandoned by 

 that able philosopher. 



M. Guy ton's pyrometer consisted of a small bar or plate of 

 platinum 4-5 millimetres (1.77 inch) long, 5 millimetres (about 

 0.2 inch) broad, and 2 millimetres (about 0.08 inch) thick, 

 placed in a groove formed in a piece of highly baked porcelain. 

 One extremity of this bar rested upon the solid end, which 

 terminated the groove, and the other pressed upon the short 

 arm of a bent lever, the longer arm of which terminated in a 

 point and moved on a pivot over the graduated arc of a circle ; 

 indicating by its motion any lengthening of the bar by increase 

 of temperature. The short arm of the lever was 2.5 milli- 

 metres and the long arm 50 millimetres in length, and the 

 latter carried a nonius by which the tenths of a degree might 

 be read off. The whole was constructed of platinum ; and a 

 plate of the same metal was made to press, in the manner of a 

 spring, upon the extremity of the index, to prevent any dis- 

 placement when withdrawing it from the fire. The description 

 of this instrument in the first Essay, published in the year 

 1803, was not accompanied by any explanatory figure ; and 

 the notice in the Annates terminates by announcing that the 



* Tome xlvi. p. 27fi. 



f )808i Second Semestre, tome ix. — 1811, ibid, tome xii. 



inventor 



