360 Patterson and Arnold — Increasing the 



send 400 impulses through, the outside circuit. If the well 



known relation — <— holds in that circuit a number of oscil- 

 -L O 



lations will follow each impulse. Among recent writers Mr. 

 Tesla is especially vague on this point. For instance on page 

 40 of his little book of " Experiments," speaking of one of 

 his dynamos he says, " It is capable of giving currents of a 

 frequency of about 10,000 a second." Here and undoubtedly 

 throughout the book he uses the expression frequency of a 

 current for its frequency of impulse ; but in his last lecture 

 he says, in regard to reducing frequency, " This I may do by 

 inserting a self induction coil in the path of the discharges or 

 by augmenting the capacity of the condensers."* Here he 

 must use frequency of the currents for frequency of oscilla- 

 tion of current because the number of electric impulses per 

 second given by the dynamo cannot be lowered by any arrange- 

 ment of self induction and capacity, while the theory of tran- 

 sient currents shows that the frequency of oscillation can be 

 reduced in either of the ways suggested in the passage just 

 quoted. The same writer expresses himself in a vague man- 

 ner on another point — the relation between the frequency of 

 oscillation in the primary and that in the secondary of a trans- 

 former. It can be shown that the frequency of oscillation in 

 the primary, in general, does not affect the electrical oscilla- 

 tions in the secondary — unless the circuits are in resonance. 

 The body of the pilot spark as shown by photographic study 

 is much greater than that of the spark due to any succeeding 

 oscillation. The sparks due to the oscillations which follow 

 the pilot spark decay rapidly according to the laws of transient 



currents in proportion to E~ 2L, so that all oscillations except 

 the first one in the primary have little effect upon a secondary 

 circuit unless the two circuits are in resonance, which in gen- 

 eral is not the case in the experiments shown by Mr. Tesla. 



The number of impulses per second in a secondary coil is 

 exactly the same as the number in the primary but the num- 

 ber of oscillations in the secondary may be greater or less 

 than those in the primary. Electrical oscillations cannot be 

 transformed in the same way as electric impulses. Although 

 this statement is susceptible of mathematical proof, we have 

 thought it desirable to study the transformation of electrical 

 oscillations by the photographic method employed by Federsen, 

 Lorenz, Trowbridge and others. The apparatus was that de- 

 scribed by Prof. Trowbridge. f The arrangement of our appa- 

 ratus is shown in fig. 1. 6 was an alternating dynamo, which 

 gave a current of 26'5 amperes at 400 complete alternations 

 per second through the primary P of a transformer the sec- 



*The Electrical World, vol. xxi, No. 22, p. 414. f Phil. Mag., Dec, 1891. 



