292 



NATURE 



[July 24, 1890 



A cause for the omission of all spectroscopic informa- 

 tion from the sections to which it respectively and pro- 

 perly belongs, and its relegation to a couple of chapters 

 in another volume, would be difficult to find. To these 

 chapters, however, for which Mr. Maunder, of Greenwich 

 Observatory, is made responsible, all matters spectro- 

 scopical have been referred, and so far as space permitted, 

 Mr. Maunder has furnished a very comprehensive sum- 

 mary of the subject he had in hand ; hence it may be that 

 Mr. Chambers has acted wisely in intrusting the discus- 

 sion of spectroscopic labours to a practical man. But 

 the first duty of the compiler of such a volume as the 

 one before us is to chronicle facts without comment or 

 bias, and to lay before his readers the conclusions that 

 have been drawn from them, leaving them to stand or 

 fall on their own merits. This, however, has not been 

 done ; many observations are introduced with disparaging 

 remarks, and conclusions deduced from them are said to 

 be " most ingenious, but far from satisfying," without any 

 evidence being adduced of their fallacy. 



We also note that the sequence of spectra observed in 

 comets as they approach to or recede from the sun, and 

 supporting the meteoritic origin of these bodies, is mildly 

 objected to. The shift in the position of the citron comet 

 band, which admits of a ready explanation when the 

 masking effect of the first flutings of manganese and lead 

 is considered, is questioned, and the sequence is said 

 to be 



" partly founded on discrepancies as to the positions 

 of some of the bands, which may prove to be significant 

 but which, more probably, are simply due to the dif- 

 ficulties of observation, and partly to the fact that the 

 yellow band of the carbon series in cometary spectra 

 does not always show the same exact correspondence 

 with the carbon band as do those in the green and blue. 

 In particular, it shows at times two or more maxima 

 within its borders, and its redward edge is rather diffused. 

 The positions of these maxima are variously given, but 

 appear to be about 5570 and 5450. There are not a few 

 instances, also, in which this yellow, or, rather, citron, 

 band has been recorded as having its sole maximum at 

 one or other of these wave-lengths. Lockyer ascribes 

 these divergences to the influence of the flutings of man- 

 ganese and lead, but, bearing in mind the great difficulty 

 of many of these observations, and that the citron band 

 is much the faintest of the three, it seems scarcely safe at 

 present to draw such an inference." 



It is here acknowledged that the citron comet band 

 has not a fixed position in the spectrum, and that 

 its appearance is not always the same. Whether it is 

 safe to conclude that the two maxima at X 557 and X 545 

 are due respectively to the flutings of manganese (558) 

 and lead (546), it is not now our place to discuss. Since, 

 however, the shift is real, it is hardly scientific to assert 

 that the measures of its wave-length given by various 

 observers are discrepancies of observation. Again, it is 

 to be regretted that in the survey of cometary spectra 

 no mention is made of Dr. Huggins's important obser- 

 vations in 1866-67 of "a bright line between b and F, 

 about the position of the double line of the spectrum 

 of nitrogen," in the spectrum of each of two small comets 

 that appeared in those years. This is also the position of 

 the chief line in the spectrum of the nebulas, and suggests 

 the connection that exists between the two bodies. 



The standard of excellence deemed necessary to establish 

 NO. 1082, VOL. 42] 



a sequence in the spectra of comets, as they approach to or 

 recede from the sun, has not been applied all through the 

 work. We find a table showing in parallel columns the 

 general agreement between the motions of stars in line of 

 sight as measured by Dr. Huggins, Mr. Maunder, and at 

 Rugby. To one unacquainted with instrumental diffi- 

 culties, the motion of stars in line of sight would appear 

 to be a quantity that may be determined with some 

 accuracy ; but to those who know the pitfalls, by far the 

 greater number of such observations appear worthless, 

 for the accuracy attained in the majority of measure- 

 ments is not sufficiently fine to allow any reliance to be 

 placed upon them. In many cases a star, according ta 

 observation, has been moving towards the earth at the rate 

 of about 50 miles a second, whilst another observation^ 

 made, perhaps, two minutes afterwards, indicated that it 

 was receding from the earth with the same velocity. It 

 is hardly just, therefore, to select certain determinations 

 and arrange them in parallel columns to demonstrate the 

 efficiency of the method adopted. At the end of the 

 discussion of these motions, a note occurs on Algol. 

 It is shown that the satellite theory of this star's varia- 

 bility, propounded by Goodricke and developed by 

 Pickering, is supported by the fact that observations of 

 its motion in line of sight, may be divided into groups, 

 which indicate that at one time it is approaching our 

 system, and at another receding from it owing to its 

 orbital velocity. With these results we have nothing to 

 do ; but, if we remember rightly, Prof. Vogel was the first 

 to demonstrate the periodic shift of the F line towards 

 the red and th e violet end of the spectrum, and in a com- 

 munication to the Berlin Academy he gave the elements 

 of the orbit traversed. This being so, it is curious to 

 find that Prof. Vogel's discussion of his photographs has 

 been omitted, although some months intervened between 

 the communication and the publication of this volume, 

 whilst Mr. Maunder's later division of his grievously 

 discrepant observations into groups has been included. 



There are a few other points to which we would 

 call the author's attention. In the portion devoted to 

 chronological astronomy, the dates of the commence- 

 ment of the seasons and their consequent lengths, are 

 given for i860, the corresponding dates for 1890 being 

 inserted in a footnote. It would have cost but little 

 trouble to substitute the latter times when bringing 

 the book up to date, and no purpose is served by the 

 present arrangement. 



A new feature, and one to be commended, is the 

 insertion of plans and specifications for small ob- 

 servatories ; this will doubtless be appreciated by 

 amateur astronomers, since the directions and measure- 

 ments which accompany them are supposed to be such 

 that any builder of ordinary intelligence will be enabled 

 to undertake the construction. It was hardly necessary, 

 however, to give the description and sketch of an obser- 

 vatory on the tower of a dwelling-house and surrounded 

 by chimneys, such as that possessed by the author. The 

 position is certainly not conducive to accurate observa- 

 tions, and the dome described appears to offer every 

 opportunity for being lifted off by a high wind and 

 deposited in the garden. 



But although the first and second volumes of this work 

 possess a few commendable features, the third volume 



