342 



Mr* R. Sabine on a Method of Measuring 



an equal instalment of the whole time during which the dis- 

 charge through the resistance-wire took place. 



The following series of observations, with their calculated 

 results, amply proves that this view was correct : — 





Excursion of the light- 





Calculated time 



Number of 



point. 



Resistance 







blows given 

 by hammer, 







of dischar- 











ging wire, 



of dis- 



of each blow, 



». 



C. 



c. 



r. 



charge, 



t 











t 



" 









ohms. 



second. 



second. 



10 



311 



109 



1500 



0000524 



0000052 



9 



311 



121 



1500 



0000471 



0000052 



8 



311 



139 



1500 



0000402 



0000050 



7 



311 



105 



1000 



0000362 



0000052 



6 



311 



120 



1000 



0-000317 



0000053 



5 



310 



138 



1000 



0000269 



0000054 



4 



310 



128 



700 



0000206 



0*000051 



3 



310 



125 



500 



0000151 



0000050 



2 



309 



118 



300 



0-000096 



0000048 



1 



309 



145 



200 



0000050 



0000050 









Mean . . . 



0000051 



In 1872 I commenced a series of experiments with the view 

 of comparing the results calculated by this method with the 

 time given by some form of chronoscope. The difficulty I 

 met with, however, was to find a chronoscope of sufficient sen- 

 sibility to give a contact or series of contacts of known dura- 

 tion. For this purpose the late Sir C. Wheatstone, with the 

 generous aid he always gave to any physical inquiry, placed 

 in my hands an apparatus which had been very ingeniously 

 designed and constructed for him some years before by Mr 

 Stroh for a different purpose ; and with this apparatus, furnished 

 with suitable electric contacts, I made several attempts to check 

 the correctness of the formula *. 



This apparatus consisted of a disk of metal with a heavy 

 rim, set in rotation by the force of a spring which was arrested 

 by striking against an anvil, whilst a pointer turning with the 

 disk struck a blow against the end of a small lever at some 

 point of the revolution determined by its position. The dura- 

 tion of the contact was arranged to last from the instant when 

 the impelling spring struck the anvil until the pointer on the 

 disk struck the lever ; and as it was assumed (and found) that 

 the velocity at any point of a single revolution was practically 

 uniform, the placing of the pointer enabled an interval of very 

 small duration to be ensured. The results which I obtained, 

 however, with this apparatus, although highly interesting, 



* I was much indebted to the industrious aid which Mr. J Rynier 

 Jones rendered me in these observations. 



