Jakuaey ]0, 1902.] 



SCIENCE. 



71 



Davis, of Harvard University, who has re- 

 cently resigned. 



SOCIETIES AND ACADEMIES. 



NEW YORK ACADEMY OF SCIENCES^ SECTION OF 

 ASTRONOMY, PHYSICS AND CHEMISTRY. 



The Section met at the Chemists' Chib on 

 the evening of December 2. The following 

 papers were presented: 



Professor M. I. Pupin described an experi- 

 mental investigation of 'Energy-Dissipation' 

 in a weak magnetic field. The substance ex- 

 perimented upon was a toroid of square cross- 

 section made up of iron plates .010 in. thick. 

 The magnetizing force was supplied by a helix 

 uniformly distributed over the core. The force 

 applied was simple harmonic of 1,800 periods 

 per second, and its amplitude could be varied 

 from to .1 C.G.S. unit. The inductance 

 and resistance of the helix was determined in 

 a Wheatstone bridge. The results obtained 

 were compared with theory. According to the 

 theory worked out by the author, inductance 

 (L) and Foucault resistance {B) is given by 

 the formulas : 



L = 2 s ' /i A log ■ 

 a 



So- 

 where 



s ^number of turns in the helix. 



i" =permeability of the iron. 



<r ^specific resistance of the iron in C.G.S. 



units. 



f=: frequency of the magnetizing force. 

 7i= height of the core in cm. 

 <i!=thickness of the plates in cm. 

 a^internal diameter of the plates. 

 Z)^ external diameter of the plates. 



Up to about .05 C.G.S. units of the magnet- 

 izing force fi is constant and equal to about 80 

 in the samples of iron employed; there is no 

 hysteresis, and the theory agrees very well 

 with experiment. Beyond that limit both L 

 and B increase; the increase of B is very 

 rapid on account of hysteresis. 



When the core is magnetized by a steady 

 force and then after removal of this force L 

 and B are measured it is found that they both 



change on account of the change of m . Their 

 values still agree with the theory within the 

 above limits of magnetization. Hence weak 

 magnetizations are not accompanied by hyster- 

 esis, both when the iron is neutral and also 

 when it is already, even strongly, magnetized. 



An increase of the permanent magnetization 

 diminishes fi , and vice versa. The maximum 

 change in fi thus obtained was 22 per cent. 



Professor J. K. Eees presented some notes 

 and lantern illustrations on observations of 

 Leonids made at Bayport by C. A. Post and 

 himself. The observations were made at Mr. 

 Post's observatory during the nights from No- 

 vember 13 to 16 (both inclusive). 



For the purpose of photographing meteor 

 trails four cameras were fastened to the equa- 

 torial. Exposures for known times were made 

 on identified parts of the sky. The results 

 showed meteor trails on the plates taken be- 

 tween midnight and sunrise of November 15. 

 Quite a i-emarkable meteor was shown on plates 

 taken with the Willard and the Anthony 

 lenses. This meteor appeared at 3.58 a. m. 

 near the radiant point and exhibited a fine 

 head and trail, whicli remained visible for a 

 minute or more. A lantern slide of this 

 meteor (made by Mr. Post) was throv^n on 

 the screen, and attention was called to the 

 peculiar details of the head and trail. Con- 

 sidering the number and the brilliancy of the 

 meteors which fell during the morning of the 

 15th, the trails on the plates are unexpectedly 

 few. 



Only during the night of November 14-15 

 was a careful attempt made to count the me- 

 teors. Miss Edith Post and Miss Greenough 

 watched the northeastern and the southeastern 

 sky. The observers at the telescope occasion- 

 ally aided in counting. Four hundred and 

 eighteen meteors, of which all but a very few 

 were well-defined Leonids, were counted. Of 

 these the greatest number was seen between 

 4.30 and 5.55 a. m., November 15, when 273 

 were counted. During the last hour the 

 shower was evidently increasing. 



The notes on ' Individual Meteors ' show 

 that many bright Leonids fell, showing trails 

 which lasted many seconds, and extended 10 

 to 30 degrees. 



