May 9, 1913] 



SCIENCE 



729 



nitudes of stars on tbe other plates can thus be 



determined on the same scale. 



Some Problems in Connection with the Millcy Way 



as shown iy Photographs with a Portrait Lens: 



Edwakd E. Barnard, Sc.D., LL.D. 

 The Spectroscopic Detection of the notation 



Period of Uranus: Percival Lowell, LL.D., 



and V. M. Slipher, Ph.D. 



By means of the spectroscope, it is possible to 

 measure the speed of approach or recession of a 

 luminous body; for the lines of the spectrum are 

 shifted toward the violet or red in proportion as 

 the body moves toward or from the observer. 

 Hence, if the image of a rotating planet be so 

 thrown upon the slit of the spectroscope that one 

 end of the slit is illuminated by light from the 

 approaching side of the planet and the other end 

 by light from the receding side, the lines will be 

 tilted through an angle which measures the speed 

 of rotation. 



In this way, from spectrograms obtained at the 

 Lowell Observatory in 1911, the authors deter- 

 mined the rotation of the planet Uranus about its 

 axis to take place in ten hours and fifty minutes, 

 in a direction opposite to that of the rotation of 

 the planets nearer the sun. Thus, for the first 

 time, an authentic determination of the rotation 

 of this planet has been made by a direct method. 

 On the Spectrum of the Nebula in the Pleiades: 



V. M. Sliphee, Ph.D. 



Two photographs of the spectrum of the faint 

 nebula near Merope, a bright star in the Pleiades, 

 were obtained in December, 1912, with a slit spec- 

 trograph attached to the Lowell 24-inch refractor. 

 The two plates were exposed five and twenty-one 

 hours, respectively. They agree in showing a con- 

 tinuous spectrum crossed by the dark lines of hy- 

 drogen and helium, the spectrum of the nebula 

 being a true copy of that of the brighter stars of 

 the Pleiades. The light of the nebula is thus 

 shown to be of stellar origin. As it seems im- 

 probable that a mass of stars, all of the same 

 spectral type as the Pleiades, should so group 

 themselves behind the Pleiades as to give the 

 appearance of a nebula, the author believes it 

 more probable that the nebula consists of diffused 

 material surrounding the stars and shining by 

 reflected star light. 



This is the first successful observation ever pub- 

 lished upon the spectrum of this faint nebula. 

 Eclipsing Variable Stars: Henry Norris Eus- 



SELL, Ph.D. Introduced by Professor William 



P. Magie. 



Progress of New Lunar Tables: Ernest W. 

 Brown, M.A., Sc.D., F.R.S. 



Saturday, April 19 — Afternoon Session 



Edward C. Pickering, D.Sc, LL.D., F.R.S., 



vice-president, in the chair 



Presentation of a portrait of William W. Keen, 

 M.D., LL.D., president of the society, by Joseph 

 G. Eosengarten, A.M., LL.D., on behalf of the 

 subscribers. 



Vice-president Pickering accepted Dr. Keen 's 

 portrait on behalf of the society. 



The rest of the session was occupied by a sym- 

 posium on Wireless Telegraphy and Telephony, 

 during which the following papers were read: 

 Badiated and Eeceived Energy : Lewis W. Austin, 



Ph.D. Introduced by Professor William F. 



Magie. 



Mathematical theory indicates that the energy 

 radiated from a radiotelegraphic antenna propor- 

 tional to the current in the sending antenna, to 

 the height of the sending antenna, to the height 

 of the receiving antenna, inversely proportional to 

 the wave-length and inversely proportional to the 

 distance between the two antennas. Since the 

 loudness of signal is proportional to the square of 

 the current in the receiving antenna, the signal 

 falls off as the square of the distance between the 

 two. 



This law has been verified by the experiments 

 made by the United States Navy Department 

 between the new high-power station at Arlington 

 and several other stations situated in and near 

 Washington. 



Observations at distances over 100 miles show 

 that in addition to the diminution in intensity of 

 signal with the distance, there is an absorption 

 either in the atmosphere or ground such that at a 

 distance of 1,000 miles over salt water with a 

 wave-length of 1,000 meters the received current 

 is only approximately 1/25; that is, the received 

 signals are reduced to about 1/600 of what they 

 would have been had there been no absorption. 



The absorption decreases as the wave-length is 

 increased, so that for communication over great 

 distances, long waves, 4,000 to 7,000 meters in 

 length, are used, whije for short distances of a 

 few hundred miles short waves are better since 

 they are radiated more energetically. These facts 

 apply to daylight communication only, which is in 

 general regular, night ranges, though greater than 

 day, being freakish and uncertain. The absorp- 

 tion over land is much greater than over water, 

 especially for the shorter wave-lengths. 



