258 
MR. DANIELL ON A NEW REGISTER-PYROMETER 
temperature, and more particularly to the purpose of connecting the indications 
of Wedgwood’s pyrometer with the mercurial scale and verifying its regularity. 
1 have since carefully studied his laborious papers in the Annales de Chimie *, 
and the Memoires de ITnstitut'f-, which appear to have been but very little 
known in this country ; and previously to entering upon the more 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. Guyton’s pyrometer consisted of a small bar or plate of platinum 45 mil- 
limetres (1.77 inch) long, 5 millimetres (about 0.2 inch) broad, and 2 millime- 
tres (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 millimetres 
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 displacement 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 Annales terminates by announcing that the in- 
ventor had at that time only begun “ a series of experiments to determine its 
march, to compare it with the pyrometer pieces of Wedgwood, and to ascer- 
tain the degree of confidence which might be placed in the indications of the 
latter.” The second Essay did not appear till the year 1808, and in it M. Guy- 
ton observes that “ many persons had expressed a wish to be made acquainted 
with the improvements which he had made in the instrument since its first 
construction ; and that he had determined in consequence to give a fresh de- 
scription of it accompanied by drawings, which might enable artists who under- 
took its construction to render it comparable. He, however, thought it right to 
give a previous account of the labours of others in this branch of science, and 
• Tome xlvi. p. 270. 1808, Second Semestrc, tome ix. — 1811, ibid, tome xii. 
