446 
MR. DANIELL ON A NEW REGISTER-PYROMETER 
with the increasing temperature, such an accordance appears to me to be per- 
fectly decisive of the accuracy of the pyrometer. 
It will be unnecessary for me to trouble the Society with the details of 
the experiments by which I determined the expansion of several other metals 
to the boiling point of mercury ; it will be sufficient to state the results in a 
tabular form. I thought that it would add much to the interest of the deter- 
mination of the total expansion to the fusing points, to determine previously 
the expansion of each to the points of boiling water and boiling mercury; 
that any alteration in the rates of expansion between these points might be 
detected. 
I must, however, make a few observations upon the general method which I 
adopted to insure an accurate determination of the former. 
Exp. 26 . Judging from the action of the pyrometer at lower heats, I expected 
that the index would continue to be thrust forward by the progressive expansion 
of any bar of metal, till its cohesion gave way and it assumed the fluid form ; 
and consequently that a register would be obtained of its maximum dilatation : 
but the difficulty consisted in applying the heat so equally that one part should 
not melt before another. The arrangement which I finally adopted to secure 
this purpose, and which was found to answer perfectly, was as follows. In 
the laboratory of the Royal Institution there is an excellent wind-furnace, from 
which proceeds a lateral horizontal flue, along which a flame may be drawn 
with any required degree of force. Into this flue open two muffle-holes, which 
give a complete view and command of the interior. From the equality of the 
draught, regulated by a register, the whole of this chamber may be kept at a 
low red, or an intense white, heat, by a proper management of the fuel in the 
body of the furnace. 
The registers of the pyrometer were prepared for the experiment by drilling 
three holes on their under sides, communicating with the cavities in which the 
bars were placed ; one at each extremity, and one in the centre. This was 
done for the purpose of allowing a vent for the melted metal, and to afford 
some criterion of the equality of the heat, by the time at which the metal ran 
from the different apertures. When the bar was properly adjusted in the re- 
gister, it was carefully placed in the hot air-chamber, in a horizontal position, 
supported at each end by a small piece of brick, at a proper distance from the 
