242 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1933 



A few more comparisons between the medieval alchemists and the 

 modem physicists may be not inapposite. Medieval alchemy was 

 guided by the principle that underlying all the different substances 

 was a prima materia, the specific differences being due to the addition 

 to this prima materia of different sets of qualities. The problem of 

 transmutation was therefore a problem of removing one set of quali- 

 ties and substituting another. At the begimiing of the last century 

 Prout suggested that hydrogen was the basis of all matter. That 

 has been proved to be not precisely true, but all forms of matter are 

 made up of protons and electrons, with a sprinkling of neutrons, and 

 hydrogen is the simplest of those forms. Transmutation has there- 

 fore become a problem of rearranging protons and electrons. This 

 is not fundamentally different from the medieval idea. Moreover, 

 by a happy inspiration the medieval alchemists were obsessed with 

 the idea that gold could be obtained by somehow treating mercury 

 with sulphur — a happy inspiration, for we now know mercury to be 

 next after gold in the periodic table of the elements — i.e., to have just 

 one more orbital electron. Finally, it is worth noting the part that 

 England has played both in alchemy and in the modern way of trans- 

 mutation. Eobert of Chester, Roger of Hereford, and Richard of 

 Wendover have their successors in Lord Rutherford, Dr. Cockcroft, 

 and Dr. Walton. 



So much for the present state of microscopic physics. A conven- 

 ient bridge to the macroscopic world is provided by the cosmic rays ; 

 they were the means by which the positive electron was discovered, 

 and on one theory they are the cause of the expansion of the universe. 

 They were called cosmic rays because they appeared to come from 

 all directions in outer space; but men of science now confess they 

 know far less about cosmic rays than they formerly thought they 

 did, and in view of doubts about their cosmic nature some workers 

 prefer to talk about " the penetrating radiation." Of its penetrating 

 nature there can be no two opinions. The rays were first discovered 

 about 30 years ago when a physicist found that an electroscope round 

 which he had piled lead sufficiently thick to shield it from all known 

 forms of radiation was nevertheless discharged. Since then a vigor- 

 ous attack on the problem of their nature has been made, an attack 

 which has increased in intensity of recent years and is now one of 

 the most fascinating of scientific pursuits. 



It is no armchair or laboratory task. The first essential is a 

 knowledge of the intensity of cosmic rays at as many times and 

 places as possible. Accordingly a great variety of observations has 

 been made. Professor Regener, of Switzerland, clearly sharing 

 Gray's faith that — 



Full many a gem of purest ray serene 

 The dark unfathom'd caves of ocean bear. 



