720 PLUCKER ON THE DETERMINATION OF THE 



measured ; but the approximative estimation explained the above 

 deviations, and the weight of the first weighing only would 

 remain slightly below that given by calculation, when we assume 

 the subsequent weighings as a basis. 



10. Instead of controlling the intensity of the current by which 

 the magnetism was excited in the electro-magnet by the insertion 

 of a galvanometer in the ordinary manner, another method of 

 proceeding appeared to me far preferable for our peculiar object. 



During the weighings described in paragragh 8, the intensity of 

 the current remained unchanged, which was known by the mag- 

 netism excited in the large electro-magnet remaining the same. 

 Since the two portions of the keeper when applied could not be 

 removed or even disturbed during the entire continuance of the 

 experiment, an iron cylinder, the upper end of which was pointed 

 conically, 27 millim. in height and 25 millim. in diameter, was 

 placed upon one of the keepers at any accurately determined spot, 

 and its magnetism estimated by the weight which was requisite 

 to withdraw from its apex a small and also pointed iron cylinder 

 weighing 1"7 grm.,and which was 16 millim. long and 4*5 millim. 

 thick. This determination was effected by the aid of a balance. In 

 these experiments, when the larger cylinder was supported upon 

 one half of the keeper, in contact with the centre of that upper 

 edge of it which was parallel to the equatorial plane and at the 

 greatest distance from it, it amounted to 352 grms. ; and this 

 weight did not vary throughout the entire duration of the obser- 

 vation more than 1 or at the most 2 grammes. 



The determination in question can be effected in two ways. 

 "When more weight is gradually added until at last the small 

 iron cylinder is drawn away, the magnet now no longer supports 

 the same weight as it was in a condition to support before the 

 separation, if it is all applied at once. To find the intensity of 

 the magnetism, we may take either the former weight, which cor- 

 responds to the gradual loading, or the weight which it imme- 

 diately supports. I prefer the former, because it allows of a more 

 accurate determination. In the above instance, the difference 

 in the two determinations amounts to some grammes ; whilst 

 the error, of which the first method of determination is suscep- 

 tible, is at the most two decigrammes*. 



11. In the different points of the approximated halves of the 



* M. vom Koike, in his Inaugural Dissertation, which has just appeared, en- 

 titled De nova magnetismimetieJidi methodo ac de rchus quihusdam hac meihodo 



