P. Thompson at once placed all
his literature and even his private notes of reference at my service.

I will now endeavor to point out the more prominent features of the
influence machines which I have present, and, in doing so, I must ask
a moment's leave from the subject of my lecture to show you a small
machine made by that eminent worker Faraday, which, apart from its
value as his handiwork, so closely brings us face to face with the
imperfect apparatus with which he and others of his day made their
valuable researches.

The next machine which I take is a Holtz. It has one plate revolving,
the second plate being fixed. The fixed plate, as you see, is so much
cut away that it is very liable to breakage. Paper inductors are fixed
upon the back of it, while opposite the inductors, and in front of the
revolving plate, are combs. To work the machine (1) a specially dry
atmosphere is required; (2) an initial charge is necessary; (3) when
at work the amount of electricity passing through the terminals is
great; (4) the direction of the current is apt to reverse; (5) when
the terminals are opened beyond the sparking distance, the excitement
rapidly dies away; (6) it does not part with free electricity from
either of the terminals singly.

It has no metal on the revolving plates, nor any metal contacts; the
electricity is collected by combs which take the place of brushes, and
it is the break in the connection of this circuit which supplies a
current for external use. On this point I cannot do better than quote
an extract from page 339 of Sir William Thomson's "Papers on
Electrostatics and Magnetism," which runs: "Holtz's now celebrated
electric machine, which is closely analogous in principle to Varley's
of 1860, is, I believe, a descendant of Nicholson's. Its great power
depends upon the abolition by Holtz of metallic carriers and metallic
make-and-break-contacts. It differs from Varley's and mine by leaving
the inductors to themselves, and using the current in the connecting
arc."

In respect to the second form of Holtz machine (Fig. 4) I have very
little information, for since it was brought to my notice nearly six
years ago I have not been able to find either one of the machines or
any person who had seen one. As will be seen by the diagram, it has
two disks revolving in opposite directions, it has no metal sectors
and no metal contacts. The "connecting arc circuit" is used for the
terminal circuit. Altogether I c