OP ARTS AND SCIENCES. 109 



VIII. 



ELECTRICAL OSCILLATIONS IN AIR. 

 By John Trowbridge and W. C. Sabixe. 



Presented May 28, 1890. • 



The experiments of Hertz on electrical waves have opened a wide 

 field for investigations in electro-magnetism. The quulitalive results 

 of Henry and of Fedderseu have been expressed in a quantitative man- 

 ner by Sir "William Thomson. Hertz, collecting together the results 

 of previous observers, and reasoning upon the factors in the formula 

 of Sir W. Thomson, — which expresses a relation between the ca- 

 pacity of a Leyden jar and the self-induction of the circuit through 

 which this jar is discharged, — has detected wave motion with its 

 nodal points and ventral segments, on a wire over which electrical 

 oscillations take place. 



Hertz has also pointed out that the experimental results confirm 

 Maxwell's theory, that light and heat are electromagnetic phenomena, 

 and that all energy comes to us from the sun in electrical pulsations. 



There can be no question of the phenomena of so-called resonance 

 discovered by Hertz. Roughly speaking, the results obtained by 

 Hertz's resonators satisfy the formula, t = 2 tt vLC. In which t is 

 the period of the electrical oscillations, L is the inductance of the 

 circuit, and C is the capacity of the jar, or that of the terminals be- 

 tween which the electrical discharge takes place. 



Professor J. J. Thomson has based a method of measuring the 

 capacities of dielectrics upon this formula and upon Hertz's work.* 



The researches of Feddersen upon electrical oscillations f were 

 more quantitative than those of Joseph Henry ; and Lorenz,t by his 

 repetition of Feddersen's results, and by his mathematical analysis 



* Proceedings of the Royal Society, June 20, 1889. 



t Poggendorff's Annalen, Vol. Clil. p. G9, 1858; Vol. CVIII. p. 497, 1859; 

 Vol. CXII. p 452, 1861; Vol. CXIII. p. 437, 1861; Vol. CXV. p. 336, 1862; 

 Vol CXVI. p. 132, 1862. 



t Wiedemann's Ann., Vol. VII p IGl, 1879. 



