102 



SCIENCE. 



[N. S. Vol. VII. No. 160. 



mental challenge. The one just discussed is an 

 example; others might easily be cited, for in- 

 stance the reasoning leading to the conclusion 

 that prominences are not of the chromosphere 

 and must, therefore, come from the outside. 

 But space forbids further discussion in this di- 

 rection. 



The training of the volunteer corps of H. M. 

 S. ' Volage ' was ingeniously planned and car- 

 ried out with pains. Parties consisting of those 

 fitted for certain classes of work were organ- 

 ized and regularly drilled for some time pre- 

 ceding the eclipse. In training the sketchers, 

 former coronas were thrown on a screen by 

 means of a magic lantern and, after some prac- 

 tice, remarkable proficiency was shown in ac- 

 curately drawing the objects, within the eclipse 

 interval of time. It is doubtful, however, 

 whether results of value are to be had from 

 drawings of the corona. Since such very short 

 exposures are required completely to fog a 

 photographic plate the question of getting faint 

 outlying details is merely one of contrast, and 

 with skillful exposure and development there 

 seems to be no reason why the camera should 

 not be considered superior to the sketch- 

 book in delineating eclipse phenomena, as it 

 has shown itself to be in innumerable other 

 branches of research. 



With regard to the bearing of solar work in 

 general on dissociation, it is safe to say that the 

 consensus of scientific opinion is not with Sir 

 Norman Lockyer. While dissociation is admit- 

 ted as a possibility, it is not considered that a 

 preponderence of evidence has given it the 

 standing of a scientific fact. It is claimed that 

 for astrophysics there is laid the foundations of 

 an exact science. But as yet the superstructure 

 has not neared completion. Peculiar character- 

 istics of spectra accompany certain physical con- 

 ditions. Good work has been done in the di- 

 rection of associating the one with the other, 

 but it is only a beginning. It is doubtful 

 whether most scientists consider that the influ- 

 ence of all our terrestrial conditions upon the 

 spectrum has been determined, or even guessed, 

 to say nothing of those which may exist in the 

 sun and stars. In time to come, when knowl- 

 edge becomes more definite on some of these 

 points, and the effect of influences probably ex- 



isting in the sun has been allowed for, we may, 

 with a mental reservation, assign the residual 

 anomalies of solar and stellar spectra to some 

 condition which we suspect to exist. Until 

 then this line of attack is to be followed with 

 caution. 



"In the course of the spectroscopic solar in- 

 vestigations which have been going on since 

 1868 I have had to point out over and over 

 again that the phenomena observed could be 

 more easily explained on the hypothesis that 

 the chemical elements with which we are fa- 

 miliar here were broken up by the great heat of 

 the sun into simpler forms ' ' etc. In the pres- 

 ent state of our knowledge it is somewhat of a 

 problem how much of a flgure the question of 

 ' ease ' should cut. We call to mind the fact 

 that, on account of insufiicient experimental data, 

 the phenomena of light were more easily ex- 

 plained to Newton by the emission hypothesis 

 than by the wave theory. And we are not all 

 Newtons. 



In closing, however, it is to be said that Sir 

 Norman Lockyer has given us an interesting 

 book, one particularly so to the general public. 

 Technical subjects are explained in simple lan- 

 guage, and the mere recital of facts and theories 

 has been relieved from time to time by digres- 

 sions upon subjects of a more human nature. 

 This is particularly so in the account of the 

 1896 eclipse expedition. It is hoped that the 

 volume will give to amateurs and others who 

 may witness the coming eclipse such a knowl- 

 edge of some of the problems awaiting solu- 

 tions as will enable them to make intelligent 

 observations which may be of interest to them- 

 selves and of use to science. 



W. H. Wright. 



Lick Obseevatoey, December, 1897. 



RECENT MATHEMATICAL BOOKS. 



Famous Problems of Elementary Geometry. An 

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 Professor of Mathematics in the Michigan 

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