This formula in which t represents the temperature in centigrades, 

 A the procentnal increase of resistance, gives, with an intensity of 

 field greater than 4500 Gauss, results, that are accurate to within 

 1 Vo, at least between the limits of temperature of 7° — 25° Celcius. 

 I obtained with this method, for tlie electromagnet of my Einthoven 

 galvanometer N". II : 

 With a field-curr. of 0.40 Amp. //^5360 in the strongest part of the field 



„ „ „ „ 1.53 „ 18900 „ „ „ 



„ „ „ „ 2.39 „ 23850 „ „ „ 



„ „ „ „ 3.49 „ 26950 „ „ „ 



„ „ „ „ 8.54 „ 31350 „ „ „ 



„ „ „ „ 8.54 ., 14150 ., „ weakest „ 



In these measurements I could not know whether the bismuth- 

 wire had actually been in the strongest part of the field. Also it 

 proved to be very difficult to measure the different parts of the field 

 very accurately. 



Therefore I have repeated the measurements with a balance of 

 Cotton, which proved to give more accurate results with less diffi- 

 culty and in less time. 



My balance was provided with a rectilinear current cairying 



conductor of 19.057 mm. length ; the arms of the balance were 



304.25 resp. 304.48 mm. long. The constant was calculated at 



p 

 5151 — in which P represented the weight placed in the scale, / 



the current strength in Amperes. The sensitiveness of the balance 

 was varied till I got about a 1 mm. deflection for 1 milligram. The 

 balance was placed on a sliding support, so that it could easily be 

 moved in the direction of the interferricum. 



In my first measurements I found with the same magnet with a 

 fieldcurrent of: 



1.50 Ampère H = W7S0 



3.48 „ 27810 



8.30 „ 31695 



which numbers probably differ less than 0.3 7u fi'om the real value. 



They agree with the values obtained before. 



With this magnetic balance I have tried to measure the local in- 

 tensity at every point of the field, with a given magnetizing current, 

 viz. 1.55 Ampère. The balance was arranged so as to place the 

 current-carrying conductor exactly in the central part of the inter- 

 ferricum, symmetrically with regard to the perforation. After the 



