CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL LABORA- 

 TORY, HARVARD UNIVERSITY 



A NEW METHOD OF IMPACT EXCITATION OF UNDAMPED 

 ELECTRIC OSCILLATIONS AND THEIR ANALYSIS BY 

 MEANS OF BRAUN TUBE OSCILLOGRAPHS. 



By E. Leon Chaffee, 



Presented by G. W. Pierce. Received July 11, 1911. 



Introduction. 



Electrical oscillations are at present of interest chiefly on account 

 of their practical applications to radio-telegraphy and radio-telephony. 

 The production and study of very rapid oscillations is also of intense 

 theoretical interest, and the applications of oscillations in high fre- 

 quency measurements and in research are of no small importance. 



Previous to the last few years practically the only method of produc- 

 ing oscillations was by means of the disruptive discharge of a condenser 

 across a comparatively long spark gap between metallic terminals in 

 air. Under such conditions a train of damped oscillations is produced 

 at each spark. The duration of these trains is very short in compari- 

 son with the interval of time between them. It is evident that such an 

 intermittent and impulsive system is ill adapted to accurate electrical 

 measurements ; and for use in wireless telegraphy the system is noisy, 

 inefficient, besides which the necessity of using high potentials in- 

 creases the danger and the difficulty of insulation. For wireless tele- 

 phony, where a regular and continuous radiation of power is necessary, 

 the long spark method is absolutely useless. 



In the last few years there have come into extensive use the short 

 gap or quenched spark method, and the arc methods of producing 

 electrical oscillations. These methods make use of the characteristics 

 of very short spark gaps between large parallel metal surfaces, or the 

 peculiar characteristics of certain forms of arcs. The advantages of 

 these methods of generating oscillations lie in their greater efficiency, 

 the absence of noise, the much greater regularity and continuity of the 



