January 14, 1921] 



SCIENCE 



43 



ica have been made by concliologists. This 

 perhaps explains the lack of morphologic de- 

 scription of the parasite from America prior 

 to 1920 since it was only of passing interest 

 to snail collectors. It would be splendid if 

 men who have the opportmiity to collect 

 certain groups of animals would save and 

 turn over the parasites and symbiotic ani- 

 mals to those interested in these particular 

 fields, and certainly we would work out life 

 cycles much faster if this attitude were taken 

 by professional collectors. 



Thomas Eyed Magath 

 Mayo Clinic, 



EocHESTER, Minn. 



SOME SIMPLE GENERATORS OF HIGH 

 FREQUENCY OSCILLATIONS 



To THE Editor of Scienck: In Science foi 

 October 15 is printed a letter from Mr. G. M. 

 J. Mackay concerning the utility of heliuni 

 as a convenient source for the production of 

 high frequency oscillations. In this connec- 

 tion it may be of interest to call attention to 

 some other simple forms of generators. 



About fourteen years ago the virriter was 

 engaged to conduct some experiments for the 

 late Professor Kristian Birkeland, of the 

 Christiania University who, from observa- 

 tions made on his electric furnaces for the 

 fixation of nitrogen, was led to believe that 

 the arc, as therein used, was partly of an 

 oscillatory nature. Birkeland's idea was to 

 produce high frequency oscillations without 

 the use of hydrogen, by simply keeping the 

 ^ arc in motion by means of a magnetic field, 

 with a view to utilizing the oscillations for 

 wireless telephony. 



His idea also proved correct, as high 

 frequency oscillations could easily he pro- 

 duced between two circular, water-cooled cop- 

 per electrodes in a radial magnetic field. 

 Telephonic messages were also transmitted by 

 these means from the university buildings to 

 Bygdoe, a distance of about two miles; but 

 the hissing noises due to the arc made imder- 

 standing very difficult. 



In the device used, the electrodes were 

 arranged horizontally, the upper electrode 



resting by its weight against the lower ona 

 On switching on the current, the upper elec- 

 trode was lifted a fixed distance by an electro- 

 magnet carrying the main current. This 

 arrangement served to start the arc auto- 

 matically whenever it went out, a thing that 

 did not happen very often, however, when the 

 apparatus and current were properly adjusted, 

 the arc sometimes burning for hours without 

 interruption. While the available voltage was 

 220, the voltage between the electrodes was 

 comparatively low, to the best of my recol- 

 lection about 50. 



The energy of the oscillations was sufficient 

 to permit a continuous spark of more than 1 

 cm. length to be drawn from the secondary 

 circiiit, easily melting the point of a thick 

 iron wire. Moreover, it was found jKissible 

 to increase this energy considerably by work- 

 ing up to three arcs in series on the above 

 voltage. As a latter arrangement did not 

 adversely affect the stability of the arc there 

 seems to be no limit to the amount of energy 

 that may thus be converted into a high 

 frequency current. 



An interesting phenomenon was discovered 

 while working this type of a generator: While 

 the oscillatory arc made the impression of a 

 rotating cluster of fat, white sparks, pro- 

 ducing a crackling sound, it would, when the 

 current was properly reduced, completely 

 change its character. The fat, white sparks 

 would gradually disappear, giving way to a 

 pale blue, almost noiseless arc, consuming 

 only a fraction of the initial current. When 

 this condition had been attained no current 

 would flow through the primary oscillation 

 circuit which could be detached without any 

 effect on the arc. The latter was also fairly 

 stable, but at a sufficient reduction of the 

 current, or weakening of the magnetic field, 

 it would go out with a sharp click. This arc 

 strikingly resembled the glow obtained by dis- 

 charges through moderately rarefied air. 



In the course of the experiments, other 

 surrounding media than air were tried, among 

 them water. One day it was found that in 

 using the latter medium it was not necessary 



