260 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 19 3 3 



by an applied voltage. However, the necessities of the case have 

 led to other suggestions for securing high voltages, because the 

 inherent limitations of electromagnetic induction devices lead to 

 prohibitive expense and complexity if voltages much above a million 

 volts are sought by such means. 



There have thus been three very interesting new developments in 

 the art of securing high voltages, or perhaps more generally, elec- 

 trified particles with those speeds that would be acquired with tre- 

 mendously high voltages. Of these, in order of apparent utility, 

 are the devices of Brasch and Lange in Germany, of Lawrence at 

 the University of California, and of Van de Graaff at the Masschu- 

 setts Institute of Technology. 



The greatest natural source of high voltage of which we have any 

 knowledge is the thunderstorm. It is estimated that the voltages in 

 lightning flashes frequency exceed a billion volts; consequently it 

 was natural for Brasch and Lange to look to the lightning flash as a 

 source of high potential and to set up what may be considered as a 

 glorified Franklin kite. Their apparatus consisted of a pair of long 

 cables suspended between mountain peaks in that region of the Alps 

 where thunderstorms are most frequent. These cables may be 

 thought of as huge wireless antennae for receiving the electrical 

 impulses of nearby lightning flashes. This was an installation of 

 real engineering proportions, since the porcelain insulators alone at 

 each end of the cable weighed upward of 2 tons. The terminals of 

 the two conducting cables consisted of large spheres, whose distance 

 apart could be varied by drawing in or letting out cable. The volt- 

 age obtained was estimated by the sparking distance between these 

 spheres and voltages were obtained ranging between 8 and 15 million 

 volts. 



Although the voltage was tremendously high, its erratic occur- 

 rence and uncontrollable nature has led Brasch and Lange to give 

 it up in favor of somewhat more conventional means of producing 

 their high voltage, and at present they are working with an impulse 

 generator. 



An extremely clever device is that invented by Prof. Ernest Law- 

 rence, of the University of California, by means of which electrified 

 particles may be given energy characteristic of several millions of 

 volts with the application of a much smaller voltage. The principle 

 is that of repeated impulses, analagous to the way by which the 

 amplitude of swing of a child in a swing may be made very great by 

 a succession of small pushes, properly timed. In Lawrence's appa- 

 ratus an oscillating voltage is applied to the ions, first in one direc- 

 tion and then in the other, while they are moving in approximately 

 circular paths in a magnetic field and conditions are adjusted so that 



