EMISSION VELOCITIES OF PHOTO-ELECTRONS. 
219 
Antimony .—The values for k and Vq for antimony are :— 
L 
372 X 
3-66 
Vo. 
3‘67 volts. 
374 
Mean . . . .S'GO 3-60 
Calcium .—Owing to its high boiling point, calcium was very difficult to distil. 
Some trouble was experienced in getting the velocity corresponding to A 1849. In the 
experiment denoted by ^ = 3'01 x 10“^^ and Vy = 2'37 volts, a slight photo-electric 
leak was obtained with \3650 which (with these constants) is just within the range 
of wave-lengths capable of producing a photo-electric effect on the energy law. This 
was the only occasion in the course of the research when X 3650 was found to produce 
a photo-electric effect:— 
k. 
3-30 X 
3-01 
3-22 
Vo. 
2‘80 volts. 
2-37 
275 
Mean . . . 3T7 
277 
Lead.- 
and Vr, 
-The experiments on lead are 
378 X 10“'" 
371 
Mean . 
375 
represented by the following values of k 
Vo. 
371 volts. 
373 
3-42 
Selenium .—All the elements that have been tested belong to groups 2, 4, and 5 of 
the periodic table. They are all metals, and are generally more or less electropositive 
in character. Selenium, which l:)elongs to group 6, is a non-metal, and is much more 
electronegative. There is not very much variation in the photo-electric behaviour of 
the seven metals whose photo-electric behaviour has been investigated, and it is 
probable that one would not get much variation until one tried an element possessing 
widely different properties. Selenium might, therefore, be expected to show some 
difference in its photo-electric properties. 
Not the slightest effect was obtained with X 2537 or with X 2257, but a well-marked 
effect was obtained with X 1849. The total photo-electric effect for this wave-length 
appeared to be quite as big as for any of the other elements previously tested. A 
very thin layer of Se was distilled first, and the maximum emission velocity corre¬ 
sponding to X 1849 was TOl volt. Then a much thicker layer was distilled, and 
2 F 2 
