306 PERIOD OF A PENDULUM. 



atus belonging to a set of Sterneck pendulums. In this way the 

 mercury cup was dispensed with, though there was, of course, 

 still an electromagnet — that of the Sterneck apparatus. The 

 curious change in the apparent period was still present. The 

 following is a typical set of observations : — 



August 2$,tli, 1912. — Steel pendulum swinging from knife 

 edge " B." Heavy weight above. Observations by Sterneck 

 apparatus, worked by Carroll chronometer — the latter about one 

 hour after winding. Observations by "descending" coinci- 

 dences only, taken at whole odd seconds. Distance of amplitude 

 scale from knife edge, 1120 mm. 



Sir J. J. Thomson on Transmutation.— In a re- 

 cent number of Nature, Prof. Sir J. J. Thomson, writing "on 

 the appearance of helium and neon in vacuum tubes," questions 

 the conclusion- arrived at by Sir William Ramsay, Prof. J. 

 Norman Collie, and Mr. Patterson with regard to the supposed 

 synthesis of helium and neon. Sir Joseph Thomson records 

 some of his own experiments which, he says, have led him to 

 a different conclusion. These experiments were undertaken in 

 order to investigate the origin and properties of a new gas of 

 atomic weight 3, which he had discovered, and which he calls 

 X;.,. Their object was to ascertain the circumstances which 

 favour the production of the gas. and the possibility of its being 

 triatomic hydrogen. He found that under circumstances similar 

 t*o those recorded before the Chemical Society., the appearance 

 of helium and neon was accompanied by larger quantities of X s . 

 The method which gave X ;i , and also the other gases, in greatest 

 abundance, was that of bombarding metals, or. indeed, almost 

 any substance, with cathode rays. From platinum he obtained 

 the most abundant supply of X... but the latter gas was also 

 obtained by a similar treatment of lead, and in both instances 

 was accompanied by appreciable quantities of helium and neon. 

 The presence of helium in Sir William Ramsay's old Rontgeil- 

 Rav bulbs Sir Joseph ascribed to the helium, thus liberated by 

 the cathode rays, either adhering to the surface, or being 

 absorbed in a much looser way than lief ore its liberation. The 

 question was: how did these gases get into the metal? It was 

 suggested that their presence may lie accounted for by partially 

 abortive attempts on the part of ordinary metals to imitate 

 radio-active substances. In the latter the a-particles are 

 emitted with such velocity that they get clear away from the 

 atom, but in the experiment- recorded by Sir Joseph Thomson 

 they have not sufficient energy to get clear, but cling to the 

 outer parts of the atom, and have to lie helped to escape by 

 Ik mbardment with the cathode rays. The conclusion, in brief, 

 is that the gases are present in the metal quite independently of 

 the bombardment, and that the action of the cathode rays is 

 merely to eliminate them. 



