May 10, 1895.] 



SCIENCE. 



519 



page 41, dated 'JO Novembre, 1S77,^ M. 

 Gervais gives the reasons for publishing the 

 second chapter first, and states that the 

 first and third chapters will probably ap- 

 pear during the year 1S7S. From this 

 statement it is evident that Froechidna could 

 searcelj' have been publislied prior to De- 

 cember 1, 1S77. The Annual Record of 

 Science and Industry for 1876, on the other 

 hand, was received at the Library of Con- 

 gi'ess, "Washington, D. C, on April 28, 

 1877. This date, however, may be the date 

 of entry for copijrit/ht, and does not neces- 

 sarily show that the book was issued on 

 April 28. A copy of the same volume in 

 the library of the U. S. Patent Office, 

 "Washington, D. C, was received early in 

 May, while the publishers, Messrs. Harper 

 & Brothers, give the exact date of publica- 

 tion as May o, 1877. 



The synonomy of the genus should stand: 



Zaf/lossiis Gill, May -5, 1877. 



Acanthofjlossus Gervais, Nov. 5, 1877 (Date 

 of reading, not of publication). 



Froechidna Gervais, Nov. 30, 1877 (Date 

 of prefatory foot-note). 



£/-((i/»/a Dubois, , 1882. 



The evidence seems sufficient to show that 

 Zaglossms was published at least as early as 

 May 5, 1877, and, therefore, antedates Acan- 

 tlioglofsu-^ by six months and Froechidna by 

 nearly seven months. T. S. Palmer. 



Washington. 



COJiJRESPOXnEXCE. 



SPECTROSCOPIC OBSERVATIONS OF SATURN AT 



THE ALLEGHENY OBSERVATORY. 



To THE Editor of Science : As certain 

 observations of mine on the spectrum of 

 Saturn have been widely noticed by the 

 daily press, and various reports have been 

 spread, some of which are correct and some 

 incorrect, but none of which were made by 

 my authority, I take this opportunitj' to ex- 

 plain the real character of the observations. 

 It is hardly necessary for me to say here 



that I have made no ' claims ' whatever re- 

 specting them. 



The observations furnish a direct proof of 

 the accepted hypothesis that the ring of 

 Saturn consists of a multitude of small 

 bodies revolving around Saturn in circular 

 orbits. The hj'pothesis is an old one, but 

 its universal acceptance dates from the pub- 

 lication of Maxwell's prize essay in 1859. 

 "While the mathematical proofs given by 

 Maxwell and his predecessors are conclusive, 

 a demonstration of the hypothesis by the 

 widely diflereut method of direct observa- 

 tion with the spectroscope is not, I think, 

 without interest. 



The proof depends upon an application of 

 the well-known principle of Doppler, by 

 which the motion of a heavenly body in the 

 line of sight can be determined by measuring 

 the displacement of a line in its spectrum. 

 Under the two difi'erent hypotheses, that 

 the ring is a rigid body, and that it is a 

 swarm of satellites, the relative motion of 

 its parts would be essentiallj' dift'erent ; 

 hence, to distinguish between these two 

 hj'potheses it is onlj- necessary to find a 

 method of sufficient delicacy, in order to 

 bring the question within the pro\'ince of 

 the spectroscope. Any method depending 

 on the successive comparison of the spectra 

 given by difi'erent parts of the ring would 

 be almost certain to foil. The method which 

 I have employed is explained below. 



If two planes, at right angles to each 

 other, are passed through the observer and 

 the system of Saturn, one (A) passing any- 

 where through the system and the other 

 (B) through its center, the velocity, resolved 

 in the direction of the line of sight, of any 

 point on the surface of the system where it 

 is intersected by plane A can be expressed 

 as a function of the perpendicular distance 

 of the point from plane B. It is only nec- 

 essary to consider the case when the plane 

 A is parallel to the major axis of the appar- 

 ent ring. On the assumption that the 



