200 Dr. Tyutlall on the Progress of the Physical Sciences : 

 bar, as exliibited in the foregoing table, by the formula 



;, = 220/tan^:Q^,. 



If we call the strength of the stream x, and the corresponding 

 magnetism ?/, then, were the law of the Russian physicists 

 general, we should have 



— = const, or ?/— const, a', 



A- 



-which is the equation of a straight line. Taking, however, the 

 stength of the stream as given in the foregoing table as abscissa, 

 and the magnetism excited as ordinate, and plotting both cor- 

 rectly, Ave obtain in the ease of the thin bar a cui-ve instead of 

 a straight line ; and moreover, the portion of this curve which 

 corresponds to high galvanic power runs nearly parallel to the 

 abscissa, thus indicating that the point of saturation had been 

 nearly attained. 



On the other hand, we find MM. Buff and Zamminer of 

 Giessen coming foi-ward to defend the conclusions of Lenz and 

 Jacobi. In a recent number of the Annalen der Chimie und 

 Pharmacie, we find the following article bearing on the subject. 



!Miiller of Freiburg (write Buff and Zamminer) has lately 

 published a series of experiments, and fi'om them derived results, 

 which, could they be regarded as the correct expression for the 

 relation of the electro-magnetism to the strength of the exciting 

 current, would completely dis])el all notion of proportionality 

 between both. In point of fact, this author rejects the law of 

 Lenz and Jacobi, and derives from his experiments the conclu- 

 sion, that the ratio of the developed magnetism to the galvanic 

 ])ower expended exhibits a remarkable decrease when that power 

 is considerable, and that for every soft iron core there is an actual 

 electro-magnetic maximum . 



This conclusion was the more unexpected by us, as haAang 

 for some time occupied ourselves with the question, under what 

 conditions does an electro-magnet attain its maximum action 

 upon a small magnetic needle at very small distances. We had 

 repeated opportunity of testing the correctness of the above law*. 

 We were, however, induced to submit the matter to a new trial, 

 which should embrace the greatest possible variations of galvanic 

 power. 



We have in no way altered the method of experiment. The 

 stream was conducted round a copper ring, in the centre of 



* That the magnetism developed is directly proportional to the strength 

 of the exciting current. 



