2f)4 MEASUREMENT OF HIGH TEMPERATURES. [bull. 54. 
is secured by the use of running water in the way described. Moreovei 
r} is small as compared with 77", because long ranges of temperature are 
met with. In view of the factor ( -?- ) it is obvious that the corrective 
, V ^o J 
factor may be made to vanish speedily by selecting terminals of larger 
bore. If 0=0", and therefore 77=77", equation (5) reduces at once to 
equation (2), supposing of course that R "=R . 
Case of two cold ends, differential apparatus. — With this result in hand 
the question with regard to the equations applying to differential appa- 
ratus of the kind sketched above (page 250) is next in order. For the case 
of the hot helix there applies as before 
~^rrr,_X rt P*-p* t R »* V (RjyV + i'»~\ l±a6 
1 + !" L 1 " 6 * Y v 1+4^^ l " J 1 +^ ,/ 
JXi 
and for the cold helix, the temperature of which is uniformly 0, 
v ?! P 2 -j) 2 t c B c * . 
1+4C~10 p V c L c 
B c 
whence, very nearly, 
V 
ri_ -[^t c V l"\R c J \B Q J I" Jl+a0"t i+ >™ J • l°l 
1+4 
1+4C/-B. 
Now, if the two helices be identical in radius and length, and if the 
times of transpiration be also identical, then, since t=t c ; L C ==L; K "=l 
B =B c -j 
rf' 
4C" V c V + V 
^-r R" 1 + ad V~ L 
l+a6" „ V+V 
(1+/^") 4 (7) 
1 + 4CAK C 
Again, if as before, R" =R =:R C , and L=L C , but the same volumes 
are found to transpire in the times t aud t c ; then, since V= V c 
tf/_ 
I" t_ V + V" 
*H 1 _l_,vtf 7" T. 
....... (8) 
- , 4C" 
t Z'-fJ"' 
X +7F 
1 4-#0 t„ L „„..* , 
V 
1 X 
4C 
1+ s 
(908) ( 
