o fixed
disks, metallic touches being fixed in suitable positions. With this
apparatus be found that small residual charges might readily be
increased. It is in this simple apparatus that we have the parent of
influence machines (see Fig. 1), and as it is now a hundred years
since Nicholson described this machine in the Phil. Trans., I think it
well worth showing a large sized Nicholson machine at work to-night
(see Fig. 11, above).

[Illustration: Figs. 1-9.]

In 1823 Ronalds described a machine in which the moving disk was
attached to and worked by the pendulum of a clock. It was a
modification of Nicholson's doubler, and he used it to supply
electricity for telegraph working. For some years after these machines
were invented no important advance appears to have been made, and I
think this may be attributed to the great discoveries in galvanic
electricity which were made about the commencement of this century by
Galvani and Volta, followed in 1831 to 1857 by the magnificent
discoveries of Faraday in electro-magnetism, electro-chemistry, and
electro-optics, and no real improvement was made in influence machines
till 1860, in which year Varley patented a form of machine shown in
Fig. 2. It also was designed for telegraph working.

In 1865 the subject was taken up with vigor in Germany by Toepler,
Holtz, and other eminent men. The most prominent of the machines made
by them are figured in the diagrams (Figs. 3 to 6), but time will not
admit of my giving an explanation of the many points of interest in
them; it being my wish to show you at work such of the machines as I
may be able, and to make some observations upon them.

In 1866 Bertsch invented a machine, but not of the multiplying type;
and in 1867 Sir William Thomson invented the form of machine shown in
Fig. 7, which, for the purpose of maintaining a constant potential in
a Leyden jar, is exceedingly useful.

The Carre machine was invented in 1868, and in 1880 the Voss machine
was introduced, since which time the latter has found a place in many
laboratories. It closely resembles the Varley machine in appearance,
and the Toepler machine in construction.

In condensing this part of my subject, I have had to omit many
prominent names and much interesting subject matter, but I must state
that in placing what I have before you, many of my scientific friends
have been ready to help and to contribute, and, as an instance of
this, I may mention that Prof. Sylvanus