320 
PROFESSOR W. a. ADAMS AND MR. R. E. DAY ON THE 
otherwise prepared for use. Each piece had a number attached to it, by which it 
was afterwards always distinguished, and by which it will always be referred to in the 
following descriptions of the experiments. 
The usual method of preparing these pieces of selenium has been as follows : — A small 
piece, varying from a quarter of an inch to an inch in length, was broken off a stick of 
amorphous selenium. A platinum wire was then taken, and one end bent round into a 
small ring, and then this ring was turned up so that its plane was at right angles to the 
rest of the wire. The rings of two such wires were then heated in the flame of a spirit- 
lamp, and pressed into the ends of the little cylinder of selenium, to act as electrodes. 
The whole was then annealed in the manner described below. After annealing, copper 
wires were soldered on to the electrodes, and the selenium was inclosed in a piece of 
glass tube, and the electrode passed through corks fixed in the ends of the tube by 
means of sealing-wax. A label with a number was then attached to one end of the 
tube, and the electrode nearest to this number was then always described as; the 
41 marked” electrode. 
A few pieces were also prepared according to the method adopted by Dr. W. Siemens. 
They were formed of two spirals of platinum wire laid upon a plate of talc in such a 
manner that they ran parallel without touching. Upon the plate a few drops of molten 
selenium were let fall, and then, before solidification, another plate of talc was pressed 
down, and the whole heated gently, so that the wires became firmly imbedded in the 
mass. The protruding ends of the platinum wires served as electrodes. These were 
soldered to silk-covered copper wires, which were passed through a cork, and the whole 
was then inserted in a test-tube. A thermometer was then inserted through the cork, 
so that its bulb was opposite to, but not in contact with, the selenium plate. 
The plates, made up according to Dr. Siemens’s method, were annealed by placing 
the test-tube in a water or a paraffin bath, which was then kept for some hours at a 
high temperature, after which the selenium was cooled down very gradually. 
The pieces made up according to the other method, and which, for the particular 
purposes of our inquiry, we have found to be the most convenient, were either annealed 
in a sand bath or in a hot-air bath. The former has been found to give the best results. 
The method of annealing is very simple. A large iron ball is heated to a bright red- 
heat in the fire and then placed in a large iron bowl filled with sand, which is heaped 
up all over the ball, and then left for an hour. The ball is then taken out and the 
pieces of selenium, wrapped up in paper, are put into the hot sand, and left there for 
twenty-four hours. On removing the selenium from the sand, its appearance is a sure 
indication whether or not the annealing has been successful ; for, in the former case, 
the bright and glossy appearance of the amorphous selenium will have changed to a dull 
slate-coloured one, and when this is the case the conductivity of the specimen will, in 
general, be found to be very good. 
In the remainder of this Paper the pieces of selenium used in each experiment will 
