hertz's researches on electrical waves. 165 



Til jmssing from tbo i)<)sili()ii 7/7 to the position V tlie lino a a' 

 rapidly turned from its position of parallelism to tbe primary circuit 

 into a position perpendicular to it. In the latter positions the sparking 

 was essentially due to the inductive action, and therefore the author 

 was justified, in his former experiments, in assuming the effect in these 

 positions to be due to induction. 



Even in these positions however, the sparking is not totally inde- 

 pendent of electro-static action, except when tbe air space is halfway 

 between tbe maximum and minimum positions, and therefore /i sin 0=0. 



Other positions of the secondary circuit. — Dr. Hertz made numerous 

 observations with the secondary circuit in other positions, but in no 

 case were any ])henomena observed which were not completely in ac- 

 cordance with theory. As an example of these consider the following 

 experiment: 



Tbe secondary was first placed in the horizontal plane in the position 

 V (Fig. 8), and the air space was in the position a^ relatively to the 

 primary. The circle was then turned about a horizontal axis through 

 its center and i^arallel to tbe primary, so as to raise tbe air space above 

 the horizontal plane. During this rotation 6 remained equal to 90^, 

 and the value of /3 remained nearly constant, but a varied approxi- 

 mately in the same ratio as cos V^, W being the angle between the plane 

 of the circle and the horizontal, for a is proportional to the number of 

 magnetic lines of force passing through the circle. Let Oo be tbe value 

 of a in the initial position, then in the other positions its value would 

 be rto cos W^ and therefore the sparking distance should be given by 

 tbe expression «o cos W -f /i, in which «„ was known to be greater than 

 ft. This was confirmed by observation, for it was found that as the air 

 space increased its height above tbe horizontal plane the sparking dis- 

 tance diminished from G millimeters down to 2 millimeters, its value when 

 the air space was at its greatest distance above the horizontal plane. 

 During the rotation through the next quadrant the sparking distance 

 diminished almost to zero, and then increased to the smaller maximum 

 of 2..") millimeters, which it attained when the circle had turned though 

 180°, and was therefore again horizontal. Similar results were obtained 

 in tbe oi)posite order, as the circle was rotated from 180° to 300o. When 

 tbe circle was kept with the air space at its maximum height above the 

 horizontal plane, and then raised or lowered bodily without rotation, 

 the sparking distance was found to diminish in the former case and to 

 increase in the latter, results completely in accordance with theory. 



Forces at greater distances. — Experiments with the secondary at 

 greater distances from the primary are of great importance, as tbe dis- 

 tribution of E. M. F. in tbe field of an open circuit is very different ac- 

 cording to different theories of electro-dynamic action, and the results 



