1895.] on the Absolute Measurement of Electrical Resistance. 617 



Summing up, then, we have during an observation one observer 

 controlling the speed by the tuning-fork method I have described ; 

 another at the galvanometer continually reversing the commutator 

 and calling out the galvanometer readings ; at the same time the rate 

 of rotation is being recorded on the tape of the Bain's telegraph 

 instrument under the watchful care of a third ; and a fourth person 

 is required to write down the readings called out from the galvano- 

 meter. The run usually lasts one, two, or three minutes according to 

 the degree of accuracy required. 



The concordance of the results obtained from successive runs in 

 measuring the same resistance is the best test of the success of the 

 combination. 



The following is a set of observations of a resistance of about 

 ^qW of an ohm made in July and August, 1893 : — 



Table III. 



July 17th, morning* 0-00050016 



July 17th, afternoon 0-00050016 



July 19th, morning 0-00050015 



August 2nd, afternoon 0*00050020 



August 3rd, morning 0-00050021 



August 4th, morning 0-00050016 



August 4th, afternoon 0-00050013 



August 5th, morning 0-00050019 



August 9th, morning 0-00050021 



August 9th, afternoon 0-00050018 



Mean 0-00050017 



The maximum divergence from the mean is • 0000000 i, or about one 

 part in 12,000. 



Here is another set, made last year in determining the value of the 

 international ohm in absolute units. 



The results are as follows, the figure in each case giving the value 

 of the international ohm in true ohms : — 



July 7th. — Standard coil carefully adjusted. Three-minute 

 tapes. 



0-999703 

 0-999761 

 0-999807 



Mean „ .. .. 0-999757 



July 9th. — No readjustment of standard coil. One-mini 



0-999757 

 0-999711 

 0-999683 



Mean 0-999733 



0-999782 ItS/i ^*— ^\£)\ 



