722 



SCIENCE 



[N. 8. Vol. XLIV. No. 1142 



It is thus evident that there is a zone in the 

 atmosphere susceptible to electrical conduc- 

 tivity beginning at about 50 miles from the 

 surface of the earth as shown by both the 

 auroral height determinations and those of 



focus of the aurora of August 26 were at a 

 height above the earth's surface not far from 

 sixty to sixty-five miles. 



C. C. Trowbridge 

 Columbia University 



Pig. 4. Comparison of the heights of the aurora, determined by Carl Stormer 's expedition 

 at Bossekop during the spring of 1913, and the heights of meteor trains. In both cases the alti- 

 tudes were determined by triangulation from two stations. 



Curve A — 2,400 determinations of the heights of the aurora. 



Curve B — the heights of the middle portion of 30 meteor trains. 



Curve C — the heights of the lower end of 21 meteor trains. 



the meteor trains. The conducting layer in 

 the earth's atmosphere which has been much 

 discussed by those interested in the propaga- 

 tion of long electric waves is usually given as 

 at an altitude of 35 to 40 miles by various 

 writers on wireless telegraphy, as based on 

 some theoretical deductions of Professor J. J. 

 Thomson. The results given above seem to 

 show that the main conducting layer of the 

 atmosphere is considerably above the altitude 

 heretofore accepted, and is at a height of 

 from 50 to 70 miles. 



The general agreement between the recently 

 determined values of auroral heights and the 

 altitude limits of the meteor train zone shown 

 in Fig. 4 is very significant, and there is thus 

 good evidence that the streamers forming the 



THE NINETEENTH MEETING OF THE 



AMERICAN ASTRONOMICAL 



SOCIETY 



The nineteenth meeting of the American Astro- 

 nomical Society was held in the Sproul Observa- 

 tory of Swarthmore College, Swarthmore, Penn- 

 sylvania, on August 30 to September 2, 1916. 

 This was the first meeting held east of the Alle- 

 gheny Mountains since 1911, intervening meetings 

 having been held in Pittsburgh, Cleveland, At- 

 lanta, Evanston, and San Prancisco. 



It has been the policy of the society for some 

 years past to hold its meetings at some one of the 

 active observatories of the country. Astronomers 

 are dependent, in a considerable measure in the 

 nature of their contributions, on the equipment of 

 their various observatories, and for a large part 

 on the character and size of the telescope. It is, 

 therefore, always of interest in the meetings to 



