ABSTEACTS: PHYSICS 81 



June 1910 to June 1911. As a rule the conductivity observations so 

 far obtained by the Department of Terrestrial Magnetism seem to indi- 

 cate a diminution of the conductivity in equatorial regions and, at any 

 rate during the daytime, in the near neighborhood of land. At the same 

 time the ratio of the conductivity of positive electricity to that for nega- 

 tive becomes smaller. The equatorial regions are perhaps regions of 

 upward currents. Gerdien's apparatus was used for the determination of 

 the specific conductivity of the atmosphere, the aluminum leaf electro- 

 scope, however, being replaced by a string electrometer as described by 

 Lutz. The amount of radioactivity obtained varied in very irregular 

 maimer, but. little activity was shown in miclocean. The potential 

 gradient observations indicate a low potential gradient, being associated 

 in general with high conductivity and vice versa. Thus, when the con- 

 ductivity was very low during a fog the potential gradient was high. 



J. A. Fleming. 



PHYSICS. — The influence of pressure on the melting points of certain 

 metals. John Johnston and L. H . Adams, Geophysical Laboratory . 

 American Journal of Science, (4) 31 : 501. 1911. 

 The authors have been engaged in developing methods and apparatus 

 by means of which it will be possible to investigate the effects of high 

 temperatures and pressures on certain systems and reactions, and 

 especially those in which water plays an important part. The work 

 has progressed until now we are able to introduce into the bomb 

 current leads and thermo-element wires in such a manner that the 

 wires are all thoroughly insulated electrically, and the joint remains 

 absolutely pressure-tight. Thus, it is possible to heat a substance to 

 somewhat over 400°, under pressures up to 2,000 atmospheres, and to 

 measure both temperature and pressure with precision. Moreover, the 

 whole system, by reason of the special methods of construction adopted, 

 is absolutely free from pressure leaks, even when the bomb is repeat- 

 edly closed and opened, disconnected from, and reconnected with, the 

 remainder of the high-pressure system. For instance, on one occasion 

 heating was continued for 30 hours continuously at a pressure of 1800 

 atmospheres, without sensible loss of pressure in the whole interval. 



With this apparatus, the melting-points of tin, bismuth, cadmium, 

 and lead were determined, first at atmospheric pressure, and afterward 

 with a gradual increase of the pressure up to 2,000 atmospheres. The 

 change of melting temperature with pressure was found to be an accu- 

 rately linear function of the pressure. 



7^ 



