Page:Collected Physical Papers.djvu/143

Rh

Both bismuth and antimony make very sensitive receivers. Moderately small E. M. F. with slight pressure is best suited for these metals.

Iron.—The action of this metal is well known. In one of my experiments I used it in connection with mercury. When the contact is very lightly made, there is a tendency towards an increase of resistance by the action of radiation. But after a time the action becomes normal, that is to say, there is a diminution of resistance.

Nickel and Cobalt.—These are also very sensitive. The surface being bright, the E. M. F. and pressure are to be adjusted with some care.

Manganese and Chromium.—These were obtained in the form of powder. Their action is similar to the other metals of this group.

Aluminium.—This also makes a very sensitive receiver.

It is somewhat difficult to adjust tin, but when this is done the metal exhibits fair sensitiveness. Lead is also sensitive. The sensitiveness of thallium is only moderate.

The specimen obtained was in the form of powder, and very tarnished in appearance. The sensitiveness exhibited was slight.