162 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



electrical oscillations, and to point out and experimentally demon- 

 strate the fact that the discharge of a condenser is under certain con- 

 ditions oscillatory, or, as he puts it, consists " of a principal discharge 

 in one direction and then several reflex actions backward and for- 

 ward, each more feeble than the preceding until equilibrium is 

 attained."'' 



This A^iew was also later adopted by Helmholz,^ but the mathemat- 

 ical demonstration of the fact was first given by Lord Kelvin in his 

 paper on " Transient electric currents." " 



In 1870 Von Bezold discovered and experimentally demonstrated 

 the fact that the advancing and reflected oscillations produced in con- 

 ductors by a condenser discharge gave rise to interference phenomena.^ 



Profs. Elihu Thomson and E. J. Houston in 1876 made a number 

 of experiments and observations on high frequency oscillatory 

 discharges.^ 



In 1883 Professor Fitzgerald suggested at a British Association 

 meeting ^ that electromagnetic waves could be generated by the 

 discharge of a condenser, but the suggestion was not followed up, 

 possibly because no means were known for detecting the waves. 



Hertz ^ discovered a method of detecting such waves by means of 

 a minute spark-gap, and before March 30, 1888, had concluded his 

 remarkable series of researches, in which for the first time electro- 

 magnetic waves were actually produced by a spark-gap and radi- 

 ating conductor and received and detected at a distance by a tuned 

 receiving circuit. 



Hertz changed the frequency of his radiated waves by altering the 

 inductance or capacity of his radiating conductor or antenna, and 

 reflected and focused the electromagnetic waves, thus' demonstrating 

 the correctness of Maxwell's electromagnetic theory of light. 



Lodge later in the same year read a paper on the " Protection of 

 buildings from lightning,"'' before the Society of Arts, in which 

 he described a number of interesting experiments on oscillatory 

 discharges. 



Great interest was excited by the experiments of Hertz, primarily 

 on account of their immense scientific importance. It was not long, 

 however, before several eminent scientists perceived that the property 



" Scientific writings of Joseph Henry, Smithsonian Institution. 

 ^ Helmholz, " Erhaltung der Kraft," Berlin, 1847. 

 <> Kelvin, Philosophical Magazine, June, 1853. 

 ^Von Bezold, Poggendorff's Annalen, 140, p. 541. 

 ^Journal Franklin Institute, April, 1876. 



f Fitzgerald, " On a method of producing electromagnetic disturbances of 

 comparatively short wave lengths." Report of British Association, 1883. 

 s Hertz, " Electric waves." 

 '^ Lodge, Society of Arts, 1888. 



