Intelligence and Miscellaneous Articles. 363 



nected through a telephone and a switch. The mirror (10 x 30 

 millim.) was fixed in a brass frame free to rotate about an axis 

 nearly parallel with the ray of light. This frame was connected by 

 an eccentric and gears to the main shaft in the workshop. By this 

 arrangement the mirror was made to oscillate through 45° about 

 300 times each second. The plane of polarization was thus twisted 

 through twice that amount, or 90°, in the same time. While this 

 oscillation was going on in the workshop, an ear placed at the 

 telephone at the other end of the circuit could easily distinguish 

 a tone, which, however, was the octave above that made by the 

 moving mirror. When the circuit was broken the sound ceased to 

 be heard, but upon again closing the tone became audible. With 

 a rate of 200 oscillations per second the note was not so easily 

 distinguished. But upon closing the circuit that peculiar sizzling 

 noise so common in telephone-circuits was heard. 



During the experiments the mirror was frequently broken by 

 the high rate of vibration. But another was quickly substituted 

 by my assistant, Mr. Baker, whom I have to thank for this and 

 the construction and management of the rotating apparatus. — 

 American Journal of Science, September 1890. 



ON THE OBSERVATION OF ELECTRODYNAMICS WAVES. 

 BY EMIL WIECHERT. 



If the occurrence of electrodynamic waves of short period is 

 observed in the manner originally indicated by Hertz, considerable 

 difficulties arise from the very feeble light of the scintillas. This 

 difficulty is greatly diminished if the scintillas are observed through 

 a microscope, which sends to the eye a very large cone of light 

 proceeding from the scintilla. 



I made up such a microscope from a system of lenses which 

 belongs to a polarizing microscope, and is used in this for obser- 

 vation with strongly convergent light, and the object-glass of a 

 telescope. The linear magnification is about fiftyfold. The mi- 

 croscope gives diffused indistinct pictures, but fulfils its purpose 

 so well that, in observing with it, the place of observation need not 

 be darkened ; in bright daylight scintillas stand out clearly which 

 the naked eye can only see with difficulty in darkness. 



Another method is not only more sensitive, but enables a large 

 number of persons simultaneously to observe the scintillas; and 

 can also be used with ordinary light. 



Imagine a secondary conductor formed just as if the object 

 were to observe the occurrence of scintillas. Suppose that at first 

 the secondary waves do not act. Let both halves of the secondary 

 conductor be insulated from each other, and one put to earth while 



