1902.] Longitudinal Magnetic Field on Internal Viscosity. 299 



field was traced to a slight extent to small uncompensated effects of 

 heating, but it is extremely unlikely that the crossing of the curves 

 is due to this cause alone, as no doubt the effect of the magnetic 

 field on the rate of subsidence depends upon the amplitude. Further 

 experiments with more nearly perfect prevention of heating effects, 

 are required to enable the dependence of the rate of subsidence on 

 amplitude to clearly disclose itself. It may be mentioned, however, 

 that the actual variations in temperature, as determined by observa- 

 tions of the temperature of the water issuing from the jacket, were 

 very slight. For example, the temperatures at the end of *each of 

 nine successive experiments — the first and last of which were made 

 with no current in the coil, and the others with currents from 2*56 to 

 6 amperes, varied from 6°*5 C. to 8° C. 



It will be noticed that in Diagram II the shape of the curves under- 

 goes change as the magnetic field is increased. This is most obvious 

 near the critical value of the field, as shown by Curves 4 and 5. 

 For Curve 4 the rate of subsidence at first is distinctly greater than in 

 Curve 5, but as the amplitude diminishes the two curves approach one 

 another, so that while, after ten, twenty, and thirty vibrations there is 

 distinctly more amplitude left in Curve 5 than in Curve 4, there is 

 practically the same amplitude left after fifty vibrations, the curves 

 being then on the point of crossing. This effect seems, as we have 

 said, to be, in part at least, due to the dependence of the magnetic 

 effect on amplitude. 



FieLol. 



DlAGEAM III. 



