Calometric Absolute Measurements. 35 



In deriving this expression it was presupposed that in place 

 of the spiral turns circular turns might be put continuously 

 filling the space occupied by the multiplier ; further, the angle 

 u of the deflection of the magnet was taken as so small that 

 one might put cosz/=l and 5 sin 2 ?* vanishingly small in 

 comparison with 1. In the observations carried out u never 

 exceeded the value 2°. The cylindrical spirals were so con- 

 structed and set up that the lengths R, D, h, and b could be 

 accurately measured to within 0*1 millim, directly with the 

 cathetometer. 



The number n of the Siemens units which represented the 

 resistance of the multiplier at the time of each observation 

 was determined by aid of a bridge arrangement, which most 

 carefully excluded all errors that might happen from extra 

 currents, variations of temperature, dissimilar positions of the 

 measuring-wire, the presence of transitory resistances, &c. 



Eighteen series of experiments were carried out, according 

 to this process, on 18 different days. The following was 

 always the order of the operations : — determination of the 



numbers; ascertaining of (^ J and I; then determination of 



the values T l3 \ 1} X 2 from twelve successive series of observa- 

 tions with the multiplier alternately "open" and "closed;" 



and, lastly, repetition of the measurement of (tt), h an d n. 



The temperature of the observation-room never varied during 

 any one series of experiments more than 0°"6 at the most, and 

 was of course closely followed. 



In order to get some light upon the trustworthiness of the 

 results obtained by this method, two groups of experiments 

 were instituted. In the first group the two spirals were 

 pushed as near together as the suspension-wire of the magnet 

 permitted (to the distance D = 39'2 millims.) ; with this the 

 difference \ 2 ~\ proved to be, on the average, 0*0296. At 

 the same time the term 



_ 3 I 2 r 4D 2 -R 2 Iff 5_ 14 R 2 4D 2 -R 2 /21 21 R 2 \ 1 



4p 2 L p 2 p 2 (3 3V + P 2 U 2 p 2 )) 



b 2 f 4 56 D 2 4D 2 -R 2 /7 21 D 2 \ ")-| 



V13 3 p 2 p 2 V6 2 p 2 ) J J 



in the above-given general expression for G had here a value 

 (about 2 per cent.) which together with the initial term 1 added 

 considerably to its importance. 



D2 



