Dike — Recent Observations in Atmospheric Electricity. 209 



rate of ionization though it does not entirely stop it, the 

 inference being that the ionization is caused by a penetrating 

 radiation from without, which can be partially screened off by 

 the lead. W. W. Strong, working at the John Hopkins Physical 

 Laboratory, has investigated the same problem, and by screening 

 the vessel on all sides except the top and noting the rate of 

 ionization, arrived at the conclusion that part of the radiation 

 comes from above. Observations in a cave gave a lower rate 

 of ionization than in the open, a fact pointing in the same 

 direction. 



There is a great field for investigation along all these lines 

 and, as I have said, one that is almost entirely neglected in this 

 country. A well-equipped observatory with opportunity for 

 research work and the development of improved apparatus 

 could add largely to our knowledge of the electrical condition 

 of the atmosphere and aid in solving some of the puzzling 

 problems, while a single observer here and there can accom- 

 plish comparatively little. The need at present is for investi- 

 gation, and persistent sustained attacks on single problems 

 rather than extended field work, though this is of value when 

 the atmospheric conditions encountered are such as can not be 

 attained at the existing observatories, as on mountain peaks, at 

 sea or in caves. 



Department Terrestrial Magnetism, 

 Carnegie Institution of Washington. 



