244 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1933 



they are detected they make their presence felt by their extraor- 

 dinary penetrating power. On account of this power they make 

 good projectiles for bombarding atomic nuclei. Mr. Blackett and 

 Dr. Occhialini were using them to bombard copper when they ob- 

 tained a shower of about 30 particles, among them several positive 

 electrons. But though the rays are comparatively rare upon the 

 earth, they are probably very important in the universe taken as a 

 whole. That is because the matter in the universe is aggregated 

 into lumps at great distances apart, but the cosmic rays appear to 

 be spread out all over space. Hence, their total effect is likely to be 

 very great. 



This line of argument gives plausibility to the cosmological specu- 

 lations of the Abbe Lemaitre, a Belgian priest who has recently 

 joined the staff of the Catholic University at Washington. The 

 Abbe Lemaitre believes that the whole universe began as a sin- 

 gle atom a few astronomical units in diameter. That allows for 

 all the nuclei of all the atoms in the universe to be packed closely 

 together. This primeval atom possessed a tendency to disintegrate, 

 and finally did burst with explosive violence, sending forth streams 

 of cosmic rays and showers of particles. Their pressure has caused 

 the universe to expand, and it is still expanding. Observational 

 evidence of this expansion is thought to be provided by the spiral 

 nebulae. We live in an island universe or nebula called the Milky 

 Way, and there are many similar nebulae, only smaller ones for the 

 most part, scattered about in space. When the light from these dis- 

 tant nebulae is split up by a spectroscope into its component colors, 

 the colors are shifted toward the red end of the spectrum compared 

 with the standard position. The most natural interpretation of this 

 shift is that the spiral nebulae are receding from us; it corresponds 

 precisely with the fall in the note of an engine's whistle as it passes 

 an observer. The velocity of recession can be measured by this 

 means as well as detected, and appears to be proportional to the 

 nebula's distance. A nebula whose light takes 3.26 million years 

 to reach the earth gives a velocity of 344 miles a second; one whose 

 light takes 150 million years on the journey gives a velocity of 15,000 

 miles a second. Of course, the shift to the red may be interpreted 

 in other ways, but that is how it would be interpreted usually. Sir 

 Arthur Eddington observed at Leicester that the Lick Observatory 

 catalog spoke of " radial velocities " in general, but cautiously used 

 the term "apparent radial velocities" for the spiral nebulae; that, 

 he said, reminded him of the clergyman who said he would arrive 

 (d.v.) on Friday, and on Saturday in any case. It should be noted, 

 however, that loss of energy by light in its passage through space 

 would account for the shift to the red, but such an explanation would 

 be entirely ad hoc. 



