720 



SCIENCE. 



[N.S. Vol. XIX. No. 488. 



of the spectrum were obtained independ- 

 ently and simultaneously in March, 1882, 

 by Sir William Huggins at Tuke Hill, 

 London, and by Dr. Henry Draper in New 

 York. 



The Tuke Hill spectrograms of the neb- 

 ula differed widely from each other, even 

 in the most prominent features ; from which 

 the conclusion was drawn by many persons 

 that the spectrum of the Orion nebula va- 

 ries rapidly with time. 



On account of the great value of accu- 

 rate knowledge at this point in stellar evo- 

 lution, it was desirable that the striking 

 discrepancies shown should be explained 

 and removed as promptly as possible. 

 With this end in view an excellent series 

 of spectrograms of the four Trapezium 

 stars and four neighboring stars was se- 

 cured in December, 1903, and January, 

 1904. These compared with spectrograms 

 previously obtained by Campbell at the 

 Lick Observatory, and by Keeler at Alle- 

 gheny, fail to confirm the changes formerly 

 suspected. 



The discrepant Tuke Hill results for the 

 nebula seem to be due to variations in 

 the time of exposure, to fortuitous arrange- 

 ments of the silver grains such as one must 

 be on his guard against in under-exposed 

 and over-developed negatives, and to the 

 fact that the commercial plates in the 

 eighties were considerably less sensitive 

 than those of the last decade. 



In case of the Trapezium stars, every 

 exposure on the star is at the same time 

 an exposure on the nebula. The particular 

 instrumental arrangement and time of ex- 

 posure may in one case emphasize the 

 spectrum peculiar to the nebula, and in 

 another that of the star, with the result 

 that spectra obtained with different instru- 

 ments and under different conditions will 

 possess comparatively few points of re- 

 semblance. We can safely say that these 

 stars are closely related to the nebula in 



chemical constitution and relatively closely 

 in physical condition. 



The results of this investigation were 

 communicated to Sir William Huggins for 

 criticism and comment. He is inclined to 

 accept in the main the conclusions reached, 

 with, perhaps, some reservation regarding 

 some of the many points involved. 



Systems of n Periplegmatic Orbits: Pro- 

 fessor Edgae Odell Lovett, Princeton. 

 (Introduced by Professor C. L. Doo- 

 little.) 



The paper on systems of periplegmatic 

 orbits was inspired by Dr. Q. W. Hill's 

 memoir on pairs of such orbits which ap- 

 peared in the current volume of the Astro- 

 nomical Journal. The notion of a peri- 

 plegmatic orbit is due to Gylden and their 

 theory has been elaborated in the introduc- 

 tory chapter of his treatise on absolute 

 orbits. The successive sections of the pres- 

 ent paper are occupied with triple and 

 ?i-ple systems of plane periplegmatic orbits. 

 The method of discussion employed is es- 

 sentially that used by Hill and the gen- 

 eralizations constructed are suggested very 

 naturally by the examples of his memoir. 

 The concluding paragraph of the note has 

 to do with certain pairs of entangled orbits, 

 periplegmatic or otherwise, whose deter- 

 mination depends either on elliptic func- 

 tions or those new uniform transcendental 

 functions recently discovered by Painleve 

 to which he is devoting a series of memoirs 

 in the Acta Mathematica. 



Palladium: Mr. Joseph Whabton, Phila- 

 delphia. 



The rare metal palladium belongs to the 

 platinum group, yet in some respects re- 

 sembles silver also. It usually occurs as a 

 companion to platinum and thus exists in 

 many places, but in such extremely small 

 quantity that until lately the reworking of 

 platiniferous residues from the various 

 mines supplied most of what appeared. 



