22 GUSTAV MAGNUS. 



He applied the principle of the stroboscopic disk in 

 observing the phenomena, by looking at the jet 

 through small slits in a rotating disk. He grouped 

 the various phenomena with peculiar tact, so that 

 those among them which are alike were easily seen, 

 and one elucidated the other. And if a final mechanical 

 explanation is not always attained, yet the reason for 

 a great number of characteristic features of the indi- 

 vidual phenomena is plain. In this respect many of 

 his researches I might specially commend those on 

 the efflux of jets of water are excellent models of 

 what Groethe theoretically advanced, and in his phy- 

 sical labours endeavoured to accomplish, though with 

 only partial success. 



But even where Magnus from his standpoint, and 

 armed with the knowledge of his time, exerted himself 

 in vain to seize the 'kernel of the solution of a difficult 

 question, a host of new and valuable facts is always 

 brought to light. Thus in his research on the thermo- 

 electric battery, where he correctly saw that a critical 

 question was to be solved, and at the conclusion de- 

 clared : ' When I commenced the experiment just 

 described, I confidently hoped to find that thermo- 

 electrical currents are due to a motion of heat.' In 

 this sense he investigated the cases in which the 

 thermo-electrical circuit consisted of a single metal in 

 which there were alternately hard portions, and such as 



