63 



EESISTANCB TO ETHEEEAL MOTION 



Br H. A. ROWLAND, N. E. GILBERT AND P. C. MCJUNCKIN 

 [Johns Hopkins University Circiilars, No. 146, p. 60, 1900] 



An attempt has been made to determine within what limits it is 

 possible to say that there is no frictional or viscous resistance in the 

 ether of space. Modern theories of magnetism are based on some kind 

 of rotary or vortical motion in the ether and if a piece of iron is mag- 

 netized we imagine that the molecules, or something about them, rotate 

 also. The existence of permanent magnets shows that any retardation 

 due to any kind of resistance must be very slight. 



In the case of an electro-magnet, any energy used in overcoming such 

 resistance, if it exists, must be derived from the exciting current and 

 the disappearance of such energy will produce an apparent resistance 

 added to that of the wire. An attempt was therefore made to deter- 

 mine whether a wire carrying a current had the same electrical resist- 

 ance when producing a magnetic field that it had when not producing it. 



The experiment consisted in winding two coils of wire together on 

 an iron core and determining whether the resistance was the same in 

 two cases : 



(1). When the current was so passed through the coils that both 

 produced a field in the same direction. 



(2). When the current was so passed that the fields produced counter- 

 balanced each other. 



The great difficulty in the experiment lay in the necessity of measur- 

 ing the resistance of a coil in which a comparatively large current was 

 flowing. In order to overcome the effect of changes in resistance due 

 to changes in temperature, two coils were wound, as nearly as possible 

 identical, and these double coils were used for the four arms of a 

 Wheatstone's bridge so that the temperature would rise in all four arms 

 equally. Each coil consisted of about 2500 turns of doubled No. 30 

 copper wire, the whole enclosed in an iron case, boiled in wax for five 

 hours and cooled in a vacuum. The insulation resistance was then 

 about eleven megohms. Iron cores were used and it was found that 

 the cases effectually protected the coils against sudden changes in tern- 



