OX THE CONTACT THEORY OF VOLTAIC ACTION. 
31 
and the difference between this and the result of the first measurement will be 
(Air^A)-f(B7Arr) — GA—BG. 
Consequently, if such experiments be made and the exact electro-motive forces of 
contact measured in a number of gases, we shall ascertain whether the contact 
difference of potentials of a substance and a gas differs much with different gases. 
Qualitative experiments in this direction have already been made with very interesting 
results by Mr. Brown, of Belfast, but his experiments differ from ours in not being 
quantitative. 
If the gas measurements such as we have indicated be extended to a good Crookes’ 
vacuum we may then possibly approximate to the real value of AB, a contact 
difference of potentials of A with B, the value that we should obtain by a measure¬ 
ment of the Peltier effect. It is therefore our purpose to extend these quantitative 
measurements not only to other gases than air but to a Crookes’ vacuum, as well as 
to measure the Peltier effects for a number of contacts of dissimilar substances. 
We have to thank two of the students of telegraphic engineeiing at the Imperial 
College of Engineering, Japan, Messrs. T. Iwata and N. Nakayama, for considerable 
assistance rendered us in the carrying out of this somewhat laborious investigation. 
