on some of the leading doctrines of caloric , &c. 375 
metallic rod a corresponding effect in expansion = 1.00. The 
next interval of Mr. Dalton's scale (equal always to 90° 
Fahr. ) can produce only \ of the effect of the first, or as 75 
to 100. The third, fourth, and fifth intervals will give the 
fractional expansions in reference to the first, of and 
about or merely a half 
No such diminution of effect was observed in the experi- 
ments ; from 392 0 to 482° F., the rod elongated as much as 
from 32 0 122 0 , or double the quantity compatible with the 
Daltonian hypothesis. Thus therefore we have a rigid, and I 
think unanswerable demonstration of the general correctness 
of the common scale of temperature, and of the extreme 
inaccuracy and inapplicability of Mr. Dalton's geometrical 
substitute. Should the preceding statement leave any doubt 
or obscurity concerning the legitimacy of the inference now 
drawn, I trust it will be entirely removed, when the details 
of the experiments are published, with drawings of the 
apparatus, in my treatise on pyrometry. 
Yet though the mercury in the thermometer tube move, 
pari passu, with a metallic rod, deemed uniform in its expan- 
sion, it does not prove perfectly equal uniformity of expansion 
to belong to the mercury. It will seem, no doubt, a para- 
doxical assertion, that of two bodies marching together, hand 
in hand, one of them may have an equable pace, while that 
of the other is regularly, but very slowly accelerated. Yet 
I think the position just. It proceeds from a circumstance 
in the thermometer sufficiently obvious, but which seems to 
have escaped our systematic writers. I do not rest the pro- 
position on any imperfection of workmanship, or supposed 
irregularity in the expansions of the glass 
