174 hertz's researches on electrical waves. 



8puce, across which sparks were made to pass by means of powerful 

 discharges from the induction coil J. The conductor was fixed at a 

 height of 1.5 meter above the base-plate of the coil, with its plates ver- 

 tical, and the connecting wire horizontal. A straight line r s, drawn 

 horizontally through the air space of the primary and perpendicular to 

 the direction of the i)rimary oscillation, will be called the base-line, 

 and a point in this situated at a distance of 45 centimeters from the air 

 space will be referred to as the null point. 



The experiments were made in a large lecture room, with nothing 

 near the base-line for a distance of 12 meters from the primary con- 

 ductor. The room was darkened during the exi)eriments. 



The secondary conductor consisted either of a circular wire C, of 35 

 centimeters radius, or of a square of wire B^ with sides 60 centimeters 

 long. The primary and secondary air spaces were both capable of ad- 

 justment by means of micrometer screws. Both the secondary con- 

 ductors were in unison with the primary, the (half) vibration period of 

 each being yoors'tfVrooiJ (1.4/liundred-millionths) of a second, as calculated 

 from the capacity and coefficient of self-induction. It is doubtful whether 

 the ordinary theory of electrical oscillations would lead to accurate results 

 under the conditions of these experiments; but as it gives correct 

 numerical results in the case of Ley den-jar discharges, it may be ex- 

 pected to be correct as far as the order of the results is concerned. 

 When the center of the secondary lies in the base-line, and its plane 

 coincides with the vertical plane through the base-line, no sparks are 

 observed in the secondary, the e. m. f. being everywhere perpendicular 

 to the direction of the secondary. This will be referred to as "the first 

 principal position " of the secondary. When the plane of the secondary 

 is vertical and perpendicular to the base-line, the center still lying in 

 the base-line, the secondary will be said to be in its " second principal 

 position." Sparking then occurs in the secondar^^ when its air space is 

 either above or below the horizontal plane through the base-line, but 

 not when it is in this plane. As the distance from the primary was in- 

 creased the sparking distance was observed to decrease, rapidly at first, 

 but ultimately very slowly. Sparks were observed throughout the 

 whole tlistance of 12 meters available for the experiments. The spark- 

 ing in this position is due essentially to the e. m. f. produced in the 

 portion of the secondary remote from the air space. The total e. m. f. 

 is partly electro static and partly electro-dynamic, and the experiments 

 show beyond the iiossibility of doubt that the former is greater, and 

 therefore determines the direction of the total e. m. f. close to the 

 primary, while at greater distances it is the electro-dynamic e. m. f. 

 which is the greater. 



The plane of the secondary was then turned into the horizontal, its 

 center still lying in the base-line. This may be called " the third prin- 

 cipal position." When the center of the circular secondary conductor 

 was kept fixed at the null point, and the air space was made to travel 



