450 Prof. F. Kohlrausch on the Determination of 





m. 



M. 



M 



s— — 

 m 



+As —As. 



Cylinder, 16 cm. long, 1 -5 cm . thick, 

 hard 



g- 

 J216 



1 109 



}■;; 



114 



144 



cm^ga 



ga sec 



20 

 29 



23 



32 



38 







8-3 







32 







8-6 

 



27 



cm 3 

 ~g" 



+0202 -0-201 

 +0-218 -0-214 



+0-216 -0-215 



+0-261 -0-265 

 +0-261 -0-264 



+0-459 

 +0-447 -0-449 



+0-335 

 +0-308 -0-305 



+0-490 

 +0-467 -0-465 



+0-341 

 +0-303 -0-304 



sec 



4200 

 6200 



5000 



3500 

 4200 







940 







3600 







1230 







3900 



Ditto, magnetized a year ago 



Ditto, newly magnetized 



Ditto, often magnetized and heated 

 for a long time 



Hollow cylinder 16 cm. long, in- 

 ternal and external diameter 1"2 

 and 1'6 cm. respectively 



Ditto, magnetized and heated a 

 year ago 



Ditto, newly magnetized 



Parallelopiped 18 X 15 X 05 cm. 

 Ditto, soft, unmagnetized 



Ditto, soft, magnetized 



Ditto, hard, unmagnetized 



Ditto, hard, magnetized 



Parallelopiped 18xl'7x0-8 cm. 



Ditto, soft, unmagnetized 



Ditto, soft, magnetized 



Ditto, hard, unmagnetized 



Ditto, hard, magnetized 





There is no decided difference in any one of these numbers 

 between the coefficient + As of increase of strength and the 

 coefficient of decrease in strength — As. 



The small differences of irregular sign are due to errors of 

 observation, and are caused, for the most part, by variations 

 in the strength of the inducing current. The mean values 

 show exact equality. 



It is thus proved that there is no inequality in the coeffi- 

 cients of increase and decrease of any such proportion as 3 : 4 

 or anything like it ; but that for practical purposes we need 

 only admit one coefficient of change of magnetism produced by 

 external forces, whether they tend to increase or to decrease 

 it. This is, of course, true only within certain limits ; how 

 far these limits extend must be left for further investigation. 

 I will only remark here that, with forces which amount to 

 about half of the earth's horizontal magnetism, more or less, 

 we arrive practically at the same numbers. 



It appears from these results that this subject has been 

 invested with unnecessary difficulty. One other point, it is 

 true, remains undecided, viz. the question whether, and under 

 what circumstances, a change of the induced magnetic moment 

 with time can be disregarded. Without doubt such an influ- 

 ence exists, but for magnets of hard steel it may no doubt be 

 neglected in practice. 



