286 
MR. DANIELL ON A NEW REGISTER-PYROMETER. 
Table of such values should be furnished for each register by the maker of the 
instrument. The following, for example, would be the proper Table for re- 
gister I, which has been so often referred to, in which the arc for the boiling 
of mercury or 600° (without adding the initial temperature) was 1° 20'. 
Table XII. 
o 
/ 
Expansion. 
Temperature. 
1 
0 
— .00872 = 
450° 
0 
30 
= .00436 = 
225 
0 
20 
= .00290 = 
150 
0 
15 
= .00218 = 
112 
0 
10 
= .00145 = 
75 
0 
5 
= .00072 = 
37 
0 
2 
= .00029 = 
15 
0 
1 
= .00014 = 
7.5 
With such a Table an intelligent workman could employ the instrument 
without any material error. Those who might object to the expense of a pla- 
tinum bar may substitute an iron one for ordinary purposes, and the cost of 
the black-lead register can never be an obstacle to its general use. Other sub- 
stances might obviously be employed in its construction, but the facility with 
which it can be worked, its small expansion, its infusibility, and the impunity 
with which it bears the most sudden changes of temperature (as when red hot 
it may even be quenched in water without injury), will probably always give 
the black-lead ware the preference. The only precaution to be taken with it 
is to expose it previously, out of the contact of air, to a heat at least as great 
as that in which it is intended to employ the instrument. 
