11 



16, 



11 



11 



17, 



11 



11 



18, 



11 



11 



19, 



11 



11 



20, 



11 



Calometric Absolute Measurements. 37 



The results found in this third series were : — 



Sept. 15, 1876, 1 S. M. U. =0-9551 x 10 10 (^j~)- 



= 0-9550 xlO 10 „' 



= 0-9548 xlO 10 „ 



= 0-9527 xlO 10 „ 



= 0-9538 xlO 10 „ 



= 0-9544 xlO 10 



According to these, in the mean, 



1 S. M. U. = 0-95430 x 10 10 /55?5?!\ 



V sec. / 



The total result of all the measurements is : — The absolute 

 value of the Siemens resistance-unit, in electromagnetic mea- 

 sure, derived from the electromotive forces and the galvanic 

 currents which are induced by slow oscillating movements of a 

 magnet in a linear conductor in its vicinity is, in the mean 



from eighteen series of trials, 0' 9 5451 x 10 10 ( ■" )• 



° ? V sec. / 



II. Ascertainment of the Absolute Value of the Siemens Mercury 

 Unit by aid of the Laics of Voltaic Induction. 



Notwithstanding the perfectly satisfactory accordance of 

 the individual results of the experiments decribed in section 

 L, I have yet derived the absolute value of Siemens' s empiric 

 resistance-unit by a second, essentially different method. While 

 in the first method the laws of magneto-induction, produced 

 by slow motion of a magnet were employed, in the second the 

 laws of voltaic induction, generated by rapidly varying gal- 

 vanic currents, were used. 



The two large cylindrical spirals which in the previous ex- 

 periments had served as multiplier, were in these new experi- 

 ments set up so that their axes fell into one and the same 

 straight line, and their middle planes had a certain distance D. 

 One of the spirals, the inducing, together with a simple circular 

 ring of 165*7 millims. radius, was inserted in the circuit 

 of a DanielFs pile, which was so constructed that it furnished 

 for hours an almost absolutely constant current. The other, 

 the induced spiral, formed with a third large cylindrical spiral 

 of 370 windings a closed circuit. The last spiral was com- 

 posed of two exactly equal halves, separated by a narrow in- 

 terval. The radius of the innermost turn of this spiral was 

 154*2 millims., that of the outermost 172*22 millims. The 

 space occupied by the windings had a rectangular cross section 

 of the breadth of 33*5 millims. ; the central planes of the two 

 halves were distant from each other 20*75 millims. Exactly 

 in the middle of the interval separating the tw^o halves was 

 placed the above-mentioned circular ring of the radius 165*7 



