HELMHOLTZ IN BERLIN 



ship was compared and contrasted. Helmholtz sug- 

 gested cigar-shaped balloons. The conditions of flight 

 also arrested his attention. He was of opinion, on 

 theoretical grounds, that the great condor of the 

 Andes has probably reached that limit of size at 

 which a bird can still soar in the air by the action 

 of the muscles of its wings ; and he despaired of 

 man ever being able to lift himself from the ground 

 by muscular action alone, however ingeniously applied. 



3. On Electrodynamics and Theories of Electricity. 



Electrical phenomena of all kinds irresistibly 

 attracted Helmholtz throughout his whole life, and 

 his works show, from the tract on the conservation of 

 energy of 1847 d wn to a paper on Clerk Maxwell's 

 Theory of the Movements of the Ether, published 

 in 1893, t ^ le vear before his death, a succession of 

 about thirty communications, mostly all of the first 

 importance. So early as 1851 he measured the 

 duration of induced electrical currents. 



For many years the conception of the action of 

 Newton's law of gravitation dominated the minds of 

 physicists, and suggested the notion of c action at a 

 distance.' That is to say, it was supposed to be possible 

 that one body might act upon another without the exist- 

 ence of any tangible or intangible intervening medium. 

 And yet this was not the opinion of Newton himself, 

 for, in his third letter to Bentley, he wrote : c That 

 203 



