284 
MR. DANIELL ON A NEW REGISTER-PYROMETER 
powder, with the iron nail and fragments of porcelain as test pieces. The fire 
was urged to the utmost ; and when it had been continued two hours the cover 
was removed, and the register, previously made red hot, was carefully intro- 
duced, the cover replaced, and the ignited fuel heaped upon it. At the expira- 
tion of a quarter of an hour it was lifted out and cautiously cooled. An excel- 
lent measure was obtained, and the arc determined to be 7° 24' = expansion 
.0645. 
The test pieces were found in the same state as in the previous experiments. 
The platinum bar was loose in the cavity, and had not altered its form ; but 
its surface had assumed a slightly crystalline texture, and it had become very 
hard and inflexible. 
The expansion registered would, upon the hypotheses before assumed of 
equal amounts of expansion denoting equal increments of temperature, indi- 
cate a heat of 3336° ; or, adding the initial temperature 65°, = 3401°. But it 
must be remembered that this is probably rather the temperature at which the 
change in the structure of the platinum took place, than the utmost heat of the 
furnace. The latter may possibly exceed the degree at which the expansion of 
the metal ceases, and at which its particles evidently form a new arrangement ; 
but this point cannot at present be determined. The coincidence of this result 
with that obtained in the former series of my experiments, is very remarkable. 
The temperature at which I obtained the fusion of cast iron at that time was 
calculated at 3479°, and was produced by the utmost energy of an excellent 
wind-furnace; and this, it will be observed, is within 80° of the present 
maximum. 
Exp. 22. Being desirous of ascertaining whether the register and platinum 
bar had undergone any change in their rates of expansion by the intense heat 
to which they had been exposed, I again adjusted the latter in the register I, 
which had now been once immersed in melted iron, and three times subjected 
to the action of the wind-furnace, and boiled them for ten minutes in mercury. 
The arc measured was 1° 19' = expansion .01148: the difference of 1' may 
safely be ascribed to the uncertainty of the reading. 
The temperatures thus determined will require correction, if we adopt the 
conclusion derived from the experiments of MM. Dulong and Petit, — that the 
dilatability of solids, referred to an air-thermometer, increases with the heat. 
