November 1, 1907] 



SCIENCE 



603 



teorites is obvious. It is probable that this 

 balancing of gravitation and light pressure 

 must be taken into account in the motion of 

 the particles supposed to constitute Saturn's 

 rings. 



When we consider the motion of a small 

 particle round the sun, we have, first, the di- 

 rect pressure lessening gravitation. If it has 

 density equal to that of the earth and diameter 

 one one-thousandth of an inch, the lessened 

 pull at the distance of the earth will imply a 

 lengthening of the year by nearly two days. 

 Secondly, the Doppler emission effect comes 

 into play, for the particle crowds forward on 

 its own waves emitted in front, and draws 

 away from those emitted behind, so that there 

 is increase of pressure in front and a decrease 

 behind. Thus there is a force resisting the 

 motion. The particle will then tend to fall 

 inwards in its orbit, and in the case considered, 

 about 800 miles in the first year. It would 

 probably move in a spiral into the sun, and 

 reach it in less than 100,000 years. A particle 

 one inch in diameter would reach the sun 

 from the earth in less than a hundred million 

 years. 



The Doppler reception effect will not come 

 into play in a circular orbit, but in an elliptic 

 orbit it acts as if it were a force resisting 

 change of distance, and therefore it tends to 

 make an elliptic orbit even more circular. 



Applying these considerations to a comet 

 regarded as a swarm of small particles coming 

 into our system, a sorting action will at once 

 begin. The smaller particles will have their 

 period of revolution lengthened out more than 

 the larger ones, and they will tend to trail be- 

 hind. The Doppler emission effect will damp 

 down the motion, and again, more markedly 

 with the smaller particles, and all will tend 

 to spiral into the sun. The Doppler reception 

 effect will tend to destroy the ellipticity of the 

 orbit, more especially with the smaller par- 

 ticles, and ultimately the particles of different 

 sizes may move in orbits so different that they 

 1 may not appear to belong to the same system. 

 In course of time they should all end in the 

 sun. Perhaps the zodiacal light is due to the 

 dust of long dead comets. 



It appears just possible that Saturn's rings 



may be cometary matter which the planet has 

 captured, and on which these actions have 

 been at play for so long that the orbits have 

 become circular. J. H. Poyntinq 



SCIENTIFIC APPOINTMENTS AT THE 

 UNIVERSITY OF WISCONSIN 



A NUMBER of changes have been made at 

 Wisconsin in the several scientific depart- 

 ments. The board of regents have named Dr. 

 Charles E. Bardeen, at present professor of 

 anatomy, dean of the new college of medi- 

 cine. The faculty of the new medical college 

 includes, besides Dean Bardeen as professor of 

 anatomy. Dr. Joseph Erlanger, professor of 

 physiology; Dr. H. L. Russell, professor of 

 bacteriology; Dr. M. P. Ravenel, professor of 

 bacteriology; Dr. W. D. Frost, associate pro- 

 fessor of bacteriology; E. 6. Hastings, assist- 

 ant professor of bacteriology ; Dr. C. A. Fuller, 

 instructor in bacteriology and assistant in the 

 hygienic laboratory; Dr. Harold C. Bradley, 

 assistant professor of physiological chemistry; 

 Dr. J. R. Blackman, assistant in physiology; 

 Dr. Richard Fischer, assistant professor of 

 pharmacy; Dr. Edward Kremers, professor of 

 pharmaceutical chemistry; Dr. Louis Kahlen- 

 berg, professor of physical chemistry; Dr. 

 Victor Lenher, associate professor of chem- 

 istry; Dean E. A. Birge, Associate Professor 

 W. S. Marshall, and Assistant Professor S. J. 

 Holmes in the department of zoology; Pro- 

 fessor R. A. Harper, Associate Professor C. E. 

 Allen and Assistant Professor R. H. Dennis- 

 ton of thejdepartment of botany; and Pro- 

 fessoji'Sr W. Snow, Professor C. E. Menden- 

 hall, and Assistant Professor A. H. Taylor of 

 the department of physics. 



Professor Mazyck Porcher Ravenel takes 

 charge of the Department of Bacteriology, suc- 

 ceeding Dr. Harry L. Russell, who was ap- 

 pointed dean of the College of Agriculture, 

 vice W. A. Henry, resigned. Dr. Ravenel has 

 been assistant medical director of the Henry 

 Phipps Institute for the Stvidy of Tuberculosis 

 in Philadelphia, and was formerly bacteriolo- 

 gist for the State Sanitary Live Stock Board 

 of Pennsylvania, where he carried on research 

 work in connection with treatment of tubercu- 

 losis and rabies. 



