184 Prof. Oliver Lodge on the Seat of the 
I do not see how it follows Fig. 12.—Thomson’s Gravitation 
on his own hypothesis that Voltaic Cell. 
his arrangement is virtually 
a reversed Lippman electro- 
meter. : 
Sir W. Thomson’s dropping 
arrangements, or voltaic cells, 
in which gravity does the work 
instead of chemical action, 
are so well known that it is 
scarcely necessary to do more 
than refer to them. Mr. 
Hart’s mercury-dropper is 
scarcely a modificaton of the 
copper-filing dropper shown 
in fig. 12. Sir William also = 
shows how to couple up such copper filings. ¢ receiver. 
cells in series*, and how to 6 inductor—zine. d copper funnel. 
construct a mechanical re- The copper filings drop negatively 
. . charged against electrical forces. 
plenisher on the Volta prin- jp you join ¢ and @ by a copper 
ciple (fig. 13). wire, you can get a current flowing 
wholly through and with copper. 
Fig. 18.—Thomson’s Voltaic Induction Machine. 
HY 
[ 
One of the inductors, T, is lined with one metal, the other with another, 
and the two connected. The carrier-wheel is rotated, and the contact- 
springs, A, A’, become oppositely charged. By afterwards charging 
the inductors with a Daniell cell, and comparing the deflection now 
produced in an electrometer connected to A, A’ with what it was 
before, measurements of Volta effect can be obtained ; or of course it can 
be made a null method. 
6. In order to give this historical sketch more complete- 
ness, it may be as well to record rapidly such other memoirs 
as I have been able to get acquainted with: it is in the highest 
degree probable that several are omitted, but I hope no very 
important ones. Prof. Wiedemann’s collection of views and 
memoirs bearing on the subject is at the end of the second 
volume of the new edition of his Hlektricitat, — 
* Electrostatic Reprints, p. 325. 
