6 Prof. A. Battelli and Mr. L. Magri on 



6. In the table given below the values of periods, as so far 

 observed, are recorded : — 



Periods of oscillation of discharges. 



a. Determinations by spark photographs. 



Feddersen (1858) from 4-46 to 1-56x10-5 sec. 



Trowbridge and Sabine (1890) 3*1 xlO-6 „ 



Bovs (1890) 3 XlO-4 „ 



Miesler (1890) from 5 to 13 xlO-6 „ 



Trowbridge and Duane (1896) 2 xl0-7 „ 



Lodge and Glazebrook (1899) ... from 1-2 to0"6xl0-3 „ 



b. Determinations by curves of charge and discharge currents. 



Tailqvist (1897) from 2-18 to 965x10-3 sec. 



Seiler(1897) from 14 to 447x10-3 „ 



Webster (1898) from 24 to 5-8 xlO-5 „ 



It should, however, be borne in mind that only Trowbridge 

 and Sabine's, Miesler's, and Lodge and Glazebrook's investi- 

 gations are really oscillation measurements by method (a). 

 Now the investigations of Trowbridge and Sabine, as well 

 as of Lodge and Glazebrook, though important on account of 

 their being made with great accuracy, are each of them re- 

 lative to one particular case only, and do not, therefore, afford 

 a complete verification of this theory. As regards Miesler's 

 researches, made in more variable conditions, it will be shown 

 below that the values derived from them cannot be said to 

 be reliable, on account of the uncertainties attending the 

 measurements of time and of spark-photographs. The in- 

 vestigations made by method (I) are, on the other hand, 

 fairly satisfactory; but the periods reached there are not 

 very short ones. 



It was therefore desirable to undertake new and more 

 extensive researches on so important a question. 



Of the two methods used in those researches that of the 

 curves of condenser charges and discharges — no sparks being- 

 comprised in the circuit — will most approach the theoretical 

 conditions which served to establish the above formula ; but 

 in addition to the imperfections proper to this method, it does 

 not refer to the cases of greatest practical importance, a spark 

 being always produced in those cases. 



As regards such imperfections as attend this method the 

 principal one is that relative to the measurements of the time 

 passing between the breaks of contacts, effected either by a 

 pendulum or a falling weight. In fact though theoretical 

 considerations may lead us to regard extremely small fractions 

 of a second as capable of being measured, those ten-millionths 

 of a second are hardly to be relied upon, as Webster assumes 



