50 . C. D. Coohsey — Secondary Cathode Rays. 



the ordinary type. This wire and gold loaf could be charged 

 to any convenient potential ; and the rate of fall of the gold 

 leaf when the rays were turned on, served as a measure of the 

 intensity of the rays from R,. Each electroscope was fitted 

 with a microscope and scale for observing the motion of the 

 gold leaf. A lead screen, F, could be slid across the window 

 in front of B by means of a screw, giving a very fine adjust- 

 ment of the amount of the radiation entering this chamber. 



The chambers, A and B, consisted of brass cylinders about 

 10 cms in diameter and 2 - 2 cms long, covered with lead on the out- 

 side. The ends of B were covered with aluminium foil. 

 The end of the wire, C, which entered A, terminated in 

 a wire ring of a diameter slightly less than the inside diameter 

 of A, and lying in a plane perpendicular to the axis of A. 

 The opening in the screen, S, opposite A was so adjusted that 

 no part of the beam from R, could fall on the ring or on the 

 walls of A. 



Brass plate holders, E and I, covered the ends of A. These 

 plate holders were made exactly alike to be interchangeable. 

 Each one consisted of two square brass plates, held together 

 with screws, and having a circular hole bored through their 

 center of about the same diameter as the inside of A. These 

 plate holders could be slid on and off the ends of A in some- 

 what the same manner as a camera plate holder, and stops were 

 so placed that they would always come to the same position, 

 with the center of the hole on the axis of A. 



In order to produce the emergence cathode rays, it was 

 necessary to pass the rays from K, through a plate of some 

 metal in which cathode rays are produced in sufficient numbers 

 to be easily measured. As these metals are relatively opaque 

 to X-rays it was necessary to use very thin sheets. Gold and 

 silver were fixed upon for this purpose. The gold leaf was 

 0-8X10 6cms thick and the silver leaf l'8XlO- 6cms . Circular 

 disks of aluminium about O'O^ 01 " 5 thick were made with a 

 diameter slightly larger than the holes in the plate holders, 

 and on one side of each was laid a thin foil of one of the above 

 metals, stuck on with a thin coat of vaseline. When thicker 

 sheets of metal were wanted more foils could be added by first 

 holding the disks, already covered with one foil, in the vapor 

 of heated vaseline, and then laying them on the foil to be 

 added. One of these disks covered with one 1 of the metals, 

 say gold, was then screwed between the two parts of each 

 plate holder and the holders placed over the ends of A with 

 the aluminium sides facing in. 



When the tube was turned on, and the wire, C, insulated 

 from the earth, there would be a motion of the gold leaf in the 

 electroscope, E,, toward one or other of the quadrants, depend- 



