588 DISCUSSION ON THE 
Naturally, this close accordance of theory and observation has made me 
believe that both ate right, and that the observed motions of the nebulae 
are genuine; so that we must accept this alarmingly rapid dispersal of 
the nebulae with its important consequences in limiting the time available 
for evolution. 
Prof. Roprrt A. MILLIKAN. 
Anyone who knows me is quite aware of the fact that I have no 
qualifications for participating in a discussion of the evolution of the 
universe, unless perhaps it be because of my interest and activity in the 
development of our knowledge of the cosmic radiation. Since, however, 
results in this field now seem destined to exert a profound, if not a deter- 
minative, influence upon all theories of stellar evolution, it may not be 
out of place for me to outline the present status of our experimental 
findings in it, and to do what I can to show whither they point. 
I note first, however, that the opening up of this amazing new field of 
knowledge is the work solely of the experimentalist. Plentiful as theorists 
have always been, especially in astronomy, and confident as they have 
always been in their conclusions, not one of them, so far as I know, who 
speculated about the nature of the universe, ever predicted cosmic rays, 
or even dreamed of their existence—certainly not sufficiently definitely to 
suggest any experiments actually to bring them to light. Prior to 1910 
not a trace of evidence had appeared that such rays existed. They had 
not even been seriously proposed. Apart from a passing suggestion by 
O. W. Richardson,” in 1906, that electroscope-discharge effects observed 
on earth might possibly have something to do with solar influences—a 
suggestion quickly negatived by the fact that these effects are as strong 
at night-time as in day-time—I can find no record of the existence any- 
where up to 1910 of any ideas even remotely related to those of the cosmic 
rays. Indeed, all the work that had been done prior to 1910, even on rays 
capable of discharging electroscopes through metal walls centimetres, or 
even inches, thick (so-called penetrating rays), was generally interpreted 
in terms of earth-rays, or of radioactive emanations getting from the earth 
into the lower atmosphere, and these are, in fact, responsible for much the 
ereater part of the then observed penetrating rays. 
In 1909 all the work that had appeared in this field up to that date 
was reviewed by Kurz,” and careful consideration given to each one of the — 
only three possible origins of the observed effects, namely: (1) the earth, 
(2) the atmosphere, and (3) the regions beyond the atmosphere. The last 
two were definitely discarded, and the conclusion drawn that there was 
not the slightest evidence for the existence of any penetrating rays other — 
than those produced by radioactive substances in the earth—this with 
full knowledge, too, dwelt upon at length in this very article, that 
half a mile of the earth’s atmosphere would absorb all such radioactive — 
radiations. Es 
When, therefore, in that same year the experimentalist, Gockel,’ took _ 
2 Richardson, Nature, 73, 607 ; 74, 55; 1906. 
8 Kurz, Phys. Zeit., 10, 836; 1909: see also Millikan, Natwre, 126, 14; 1930, for 
historical studies. 
4 Gockel, Phys. Zeit., 11, 280; 1910: also 12, 597; 1911. 
aA Cathy che 
