SIR W. CROOKES ON ACQUIRED RADIO-ACTIVITY. 
439 
radiation extending some distance round the diamond (six or eight diameters), and 
the lead pillars showed strong shadows (Plate 9, fig. l). 
22. The same experiment was repeated three times with the interposition of 
one, two, and three thicknesses of aluminium foil O'Ol mm. thick, each was exposed 
the same time (two hours), and all were developed together. Each showed strong 
action near the diamond. One thickness allowed the shadow of the lead pillars 
to be easily seen. Two thicknesses showed the shadow with difficulty, and three 
thicknesses only showed the shape of the diamond itself. 
23. The crystal (17) was removed from its circle of lead pillars (21). A small 
cell of brass tube 0'5 inch in diameter had six slots cut in it with a file. The 
diamond was mounted in such a position that the three corners of the triangular 
surface that touched the film should come opposite three of the slots. These 
experiments show that the diamond is giving off /3-rays copiously (fig. 2). 
y-j Rays from the Radio-active Diamond. 
24. The diamond (17) crystal was fixed with its sharpest point upwards in a 
small thick cell of brass. Exactfy over the point was a small hole 0'5 mm. in 
diameter and 5 mm. long. On the top was a piece of sensitive film enclosed in 
black paper. The whole was kept in the dark for three hours, when a fair image 
of the hole was obtained on development. The apparatus, with another sheet of 
sensitive film in it, was fixed between the pointed poles of a powerful electro¬ 
magnet, and a current of 30 amperes was passed through for three hours. The 
current was then shut off’, and the film shifted sideways for half an inch, and the 
action of the diamond without the magnetism was allowed to go on for another 
three hours. It was then developed, and both spots appeared about the same 
intensity. 
25. The diamond crystal (17) in its brass box had a thin plate of clear mica 
put over the hole, and a sheet of lead over that. All was wrapped in sheet lead, 
and so kept for about six months. There was an extremely faint but hardly 
appreciable darkening of the mica at the position of the hole. 
26. After the above experiment the diamond was kept in its brass box for 
two years, and then laid on a sensitive film and kept there for three hours. On 
developing, a spot of action was seen, showing that the diamond was still radio¬ 
active. It was removed from its brass cell and examined in the dark on a blende 
screen. It gave plenty of scintillations easily visible without a lens. Experiments 
showed that it still gave out, along with a-rays, also /3- and y-rays (10, 19, 42, 43). 
27. A small light-tight box was fitted as a camera. The arrangements were such 
that the image on the sensitive film was 1‘5 times the size of the object. A photo¬ 
graph of the radio-active diamond (17) was taken by the light of its own scintillations 
