260 
MR. DAN I ELL ON A NEW REGISTER-PYROMETER 
not expect that the platinum pyrometer could ever come into general use : 
“ enfin, ces corrections ne peuvent manquer d’aj outer a l’utilite du pyrom&tre 
d’argile, soit dans les travaux chimiques, soit dans les arts ; quand meme le 
pyromhtre de platine, plus exact mais moins usuel, serait reserve pour en as- 
surer la marche, et pour servir a des recherches plus importantes.” 
M. Guyton, however, although he abundantly proves the incorrectness of 
Mr. Wedgwood’s estimate of the higher degrees of temperature, is very far in- 
deed from establishing the point at which he so earnestly laboured, namely, 
the regularity of the contraction of the clay pieces ; or from substituting a more 
correct value of the degrees throughout the whole range of the gauge than the 
one which he so completely overturned. His comparative experiments with 
the platinum pyrometer, at the boiling points of mercury and linseed oil, and 
the melting point of antimony, led him to reduce the equivalent of each degree 
from 130° Fahr. to G2°.5. The zero point of the clay pyrometer was thus car- 
ried back to 517° instead of 1077° ; but it seems to have escaped his notice that 
this zero point was declared to be a red heat visible in the day-light, — a descrip- 
tion which cannot be mistaken, and which clearly could not be below the 
temperature of boiling oil, melting lead, or boiling mercury ; all of which are, 
however, placed above it in M. Guyton’s table. M. Guyton also places the 
melting point of silver at the 22nd degree of Mr. Wedgwood’s scale instead of 
the 28th, which was, according to his own determination, a correction first sug- 
gested by Sir James Hall in the 9th volume of Nicholson’s Journal. Taking 
the value’of each degree at 62°.5 Fahr., it fixes this point at 1892° Fahr., which 
agrees very nearly with my own experiment in the paper before alluded to ; 
but continuing the calculation up to the melting point of iron, upon the sup- 
position of an uniform progression, the 130th degree corresponds with 8696° 
Fahr., which, although only about half the amount 17977° assigned by Mr. 
W edgwood, is very far removed from the result of my calculation 3479°. 
Nevertheless, it is a curious fact, that M. Guyton’s Essay contains proof that 
his determination is erroneous, and that mine is a near approximation to the 
truth. As a collateral means of verifying the indications of instruments in- 
tended to measure high degrees of temperature, he refers to the calorimeter as 
capable of affording the necessary data by a calculation from the amount of 
heat communicated to known quantities of fire or water by bodies in a state of 
