156 ECORDS 



SECTION OF ASTRONOMY, PHYSICS AND 

 CHEMISTRY. 



December 2, 1901. 



Section met at 8:15 P. M., Prof. William Hallock presiding. 



The minutes of the last meeting of Section were read and ap- 

 proved. 



The following program was then offered : 



Prof. M. I. Pupin, Energy Dissipation in a Weak Mag- 

 netic P'lELD. 



Prof J. K. Rees and 0. A. Post, Observations of Leonids 

 MADE AT Bayport L. I., from Nov. 13th to i6th inclusive. 



Summary of Papers. 



Prof. Pupin described an experimental investigation of the 

 dissipation of energy in a weak magnetic field. The substance 

 •experimented on was a toroid of square cross section made up 

 of iron plates .010 of an inch thick. The magnetizing force 

 was supplied by a helix uniformly distributed over the core. 

 The force applied was a simple harmonic of 1800 periods per 

 second and its amplitude could be varied from o to . i C. G. S. 

 units. The inductance and resistance of the helix was deter- 

 mined in a Wheatstone bridge. The results were compared 

 with the theory worked out by the author. 



It was found that up to about .05 C. G, S. units of the mag- 

 netizing force the permeability of the iron was constant and equal 

 to about 80, in the samples of iron employed : there was no 

 hysteresis and the theory agreed very well with experiment. 

 Beyond the above limit both the inductance (Z) and the Foucault 

 resistance (R) increased. The increase of R was very rapid on 

 account of hysteresis. 



When the core was magnetized by a steady force, and after the 

 removal of the force L and R were measured, it was found that 

 both were changed on account of the change of permeability, 

 but within the above limits their values still agreed with the 

 theory. Hence weak magnetizations are not accompanied by 



