( 01 ) 



From these observations we deduce: 



599,9 N. 599,7 



600,2 E 599,3 



600,1 F 599,4 



The difference of deviation, caused by X, must in my opinion, 

 be ascribed to the influence of temperature, in consequence of which 

 the potential of the charging battery was changed. If greater accuracy 

 is desired, it is necessary to keep the temperature of the charging 

 battery and of the Clark cell constant; in these experiments the 

 Clark cells were placed in glass vessels filled with paraffine oil, 

 and care was taken that the temperature could not differ much 

 during the night preceding the experiments. 



From this series of observations is seen : 1". that with this platinum 

 wire the elastic hystei'esis may be quite neglected and 2°. that with 

 one observation a difference of potential of 1,4 volt may be measured 

 to at least ^lo percent. 



Another great advantage of this method is that the Clark cell 

 does not yield a current. 



If, without examining in how far the deviation of the electro- 

 meter and the difference of potential are proportional, we wish to 

 measure the intensity of an electric current, the resistance must be 

 chosen in such a way, that at its ends the difference of potenti;il 

 is nearly equal to that of a Clark cell, and this must be compared 

 with a Clabk cell. So a resistance of 0.14 ohm is required for 

 currents of about ten ampere; this resistance must be constructed 

 in such a way that the current cannot cause great differences of 

 temperature; therefore ten German Silver wires of Vo mm. diameter 

 and about ^2 M. long were arranged in parallel and placed in a 

 large basin filled with paraffine oil; because of the small tempera- 

 ture coefficient it is sufficient to know the temperature to within 

 three degrees without making a mistake greater than Vio percent. 

 Tlie resistance itself was determined in the usual way with the 

 Wheatstone bridge. Many measurements of the intensity of cur- 

 rents have been made and ampere-meters have been tested with 

 this resistance i). 



') That it ia necessary to teat ampere-meters repeatedly is proved by the fact, that 

 on an ampere-meter of Carpbntieh a current of 10 ampere was marked in 



March '95 with 13 amp. 



January '96 " 13,5 i, 



March '97 " 14 '/ 



October '97 "16 // 

 Evidently the magnet has been losing its strength continually. 



