226 



SCIENCE 



[N. S. Vol. XXXI. No. 789 



consciousness, irreducible to complexes of sen- 

 sations and images, and of a kind hitherto 

 unrecognized by most psychologists. Our au- 

 thor disbelieves altogether in the elementary 

 character of such thoughts; he emphasizes the 

 crudeness of the methods employed, and be- 

 lieves that more refined study will probably 

 reveal vestiges of images and sensations of 

 bodily attitudes, as components of vchat has 

 been called imageless or non-sensorial thought. 



In addition to its main purpose, the book is 

 valuable as throwing a clearer light than any 

 of his previous writings on the author's guid- 

 ing principles in psychologizing. 



r. s. woodworth 



Columbia Univeesitt 



SOME SUGGESTIONS FOR THE STUDY OF 

 COMETS^ 



Comets are, probably, the most mysterious 

 of all celestial objects. Whence they come; 

 whither they go, when they leave forever; 

 where they gather fresh material, if they do, 

 and how; their mechanical structure; the 

 forces that commonly bind them together; the 

 other forces that sometimes tear them apart; 

 the origin of the curious knots, twists and 

 streaks in their tails; and why it is that they 

 are self-luminous, are among the things con- 

 cerning comets we should like to know, but 

 which, at present, no physicist and no as- 

 tronomer can tell us. 



It is but natural therefore that the return 

 and near approach of Halley's comet should 

 arouse unusual interest and activity in the 

 study of these strange objects, for it is bring- 

 ing us a rare chance, especially if, as seems 

 likely, the earth should pass through its tail, 

 of learning much that we would like to know 

 in regard to comets and their accompanying 



' This paper was prepared at the request of the 

 comet committee of the Astronomical and Astro- 

 physical Society of America for inclusion in its 

 circular respecting observations of Halley's comet. 

 Through causes for which its author is in no way 

 responsible it did not reach its destination in 

 time to be so used and the committee now seeks 

 to give it publicity through the pages of Scie:^ce 

 and such other journals as may choose to repro- 

 duce it. 



phenomena. But to make such a study most 

 efficient it is necessary to consider what phe- 

 nomena roay possibly be expected, and how 

 they can be observed. 



These form two distinct groups, namely: 

 (1) celestial, astrophysical in the main; (2) 

 terrestrial, chiefly meteorological. Among the 

 former are: 



(o) Gross Appearances. — This includes all 

 distinctive markings, such as bright patches; 

 streaks, both straight and twisted; number, 

 direction and shape of tails; time and manner 

 of beginning and ending of tails; and any 

 other such phenomenon as may present itself 

 to the observer. A photographic record, as 

 nearly as practicable continuous, should be 

 taken of these phenomena for future study, 

 but it would be well to supplement the photo- 

 graphs by numerous eye observations. 



Any one expecting to do work of this nature, 

 and there are many observatories adequately 

 equipped for it, would do well to consult Pro- 

 fessor E. E. Barnard, of the Terkes Observa- 

 tory, either directly or through his papers on 

 comets. 



(6) Bpectrum. — Visual and photographic 

 analysis of the light should be applied to the 

 comet in detail — to the jets and envelopes in 

 and about the head, to the streaks in the tail 

 and to all portions bright enough to yield 

 results. 



Such a program, while of decided value, can 

 not profitably be undertaken except by those 

 observatories especially well equipped for this 

 sort of work. 



(c) Polarization. — It is knovtTi that the light 

 of comets is polarized to some extent, from 

 which it is inferred that a part of their lumin- 

 osity is due to reflected sunlight, but this 

 phenomenon needs further examination, and, 

 in particular, separation from sky polariza- 

 tion. It would be well to compare the polar- 

 ization of that part of the comet where a right 

 angle exists between the directions from it to 

 the sun and the earth, respectively, with the 

 polarization of other portions. If the particles 

 of the comet are small in size, compared with 

 the cube of an average wave-length of light, 

 then, as Eayleigh has shown, there will be 



