April 2\. 1881] 



NATURE 



575 



demonstrations, which especially mark his powers of 

 research and reasoning, was that of the motion of the sun 

 and solar system in space and the direction of this 

 translation, which, considered generally, has received 

 confirmation from more recent and refined investigation. 

 Maskelyne had determined the proper motions of a limited 

 number of the brighter stars, and Lambert, Mayer, and 

 Bradley had thrown out ideas upon the subject, and, fol- 

 lowing up their suggestions, he showed that the sun was 

 really in motion towards a point in the constellation 

 Hercules, and assigned " the apex of solar motion " with 

 what Holden considers an astonishing degree of accuracy- 

 His second paper on this subject (1S05) his biographer 

 views as " the best example that can possibly be given of 

 his marvellous skill in reaching the heart of a matter, and 

 it may be the one in which his philosophical powers 

 appear in their highest exercise." 



To gain a knowledge of the "Construction of the 

 Heavens," as Herschel termed it, of the laws of distribu- 

 tion of the stars generally, the star-clusters and nebulae 

 in space, was confessedly a main object of his astronomi- 

 cal labours, and the memoirs bearing upon this subject 

 extend over the whole period of his scientific career. 

 For this purpose he adopted a system of star-gauging, 

 which in practice consisted in pointing his 20-feet reflec- 

 tor towards various parts of the sky and counting the 

 number of stars in a field of view 15' in diamjter. In 

 this way, by methodical observation, the great differences 

 in number of the stars in certain portions of the sky over 

 those in other directions were reliably defined, and in 

 extreme cases the difference was very marked, as in one 

 mentioned by Holden, where in R.A. igh. 41m., N.P.D. 

 74° 33', in the constellation Sagitta, the number of stars 

 per field was found to be 588, while in R.A. i6h. lom., 

 N.P.D. II3'^4' in Scorpio it was only I'l — " cin Loch iin 

 Him»icl .'" In this part of his review the author briefly 

 touches upon the views entertained by Herschel at various 

 periods between 1784 and 1817; he considers that while 

 at the commencement of his researches the whole subject 

 was in utter confusion, as they progressed data for the 

 solution of some of the most important questions were 

 accumulated, and the results of Herschel's whole labours 

 form the groundwork upon which future investigators 

 must build. " He is the founder of a new branch of 

 astronomy." 



The researches for a scale of celestial measures, on 

 light and heat, &c., on the dimensions of the stars, on 

 the variable emission of light and heat from the sun, are 

 briefly referred to. Herschel's observations on the spectra 

 of the fixed stars have been, we believe, very much over- 

 looked. In his memoir in the Pliilosophical Transactions 

 for 1814 he inentions that in 1798 he made some experi- 

 ments on the light of a few of the stars of the first magni- 

 tude, by a prism applied to the eye-glasses of his 

 reflectors, adjustable to any angle and direction, with the 

 following results: — The light of Sirius consists of red, 

 orange, yellow, green, blue, purple, and violet ; a Orioiiis 

 contains the same colours, but the red is more intense 

 and the orange and yellow are less copious in proportion 

 than they are in Sirius. Procyon contains all the colours, 

 but proportionally more blue and purple than Sirius. 

 A returns contains more red and orange, and less yellow 

 in proportion than Sirius. Aldebaran contains much 



orange and very little yellow, a Lyres contains much 

 yellow, green, blue, and purple." Holden suggests that if 

 we were to attempt to classify these stars by Herschel's 

 observations alone we should put Sirius and Procyon into 

 one type of stars, which have all the colours in their 

 spectra ; .4rcturus and Aldebaran would represent another 

 group, with a deficiency of yellow and an excess of orange 

 and red in the spectrum ; a Orionis would form a type of 

 those stars, with an excess of red and a deficiency of 

 orange ; and a Lynr would represent a sub-group of the 

 first class. The correspondence with Secchi's types and 

 representatives is almost complete. 



There remains one other great section of Herschel's 

 researches and discoveries, that relating to the nebulx 

 and clusters of stars. When he commenced his observa- 

 tions in 1774 very few of these objects were known. 

 Messier's catalogue of sixty-eight such objects did not 

 appear till 17S4, and they were chiefly objects found in 

 his long-continued search for comets. Lacaille contri- 

 buted twenty-eight from his observations at the Cape of 

 Good Hope. Herschel discovered more than 2500, which 

 he distributed in classes as follows : — Class I. " Bright 

 nebulii;" (28S in all); II. "Faint nebula; " (909) ; III. 

 "Very faint nebute" (984); IV. "Planetary nebulae" 

 (79); V. "Very large nebulae" (52); VI. "Very com- 

 pressed and rich clusters of stars" (42); VII. "Pretty 

 much compressed clusters" (67); VIII. "Coarsely scat- 

 tered clusters" (88). In addition he pointed out large 

 spaces of the sky covered with very diffused and faint 

 nebulosity, which do not appeaj^ to have been re-observed. 

 Holden advises that they should be sought for with a 

 powerful refractor, which would be less open to illusions 

 than Herschel's reflectors, and that the instrument should 

 be used in the way he adopted — in sweeping. 



Throughout Prof. Holden's interesting memoir there is 

 evinced the same enthusiastic admiration of Herschel 

 and his scientific labours, and he concludes in the same 

 strain. " He was born with the faculties which fitted 

 him for the gigantic labours which he undertook, and he 

 had the firm basis of energy and principle which kept 

 him steadily to his work. As a practical astronomer he 

 remains without an equal. In profound philosophy he 

 has few superiors." 



Lists of Herschel's scientific memoirs and of works 

 bearing upon them, are appended to the volume which 

 has formed the subject of our notice, and which, if it has 

 a fault, is of only too limited extent to do full justice to a 

 long life of discovery and research. We will reiterate 

 the hope expressed by Prof. Holden in his preface, as 

 we understand it, that some member of Sir William 

 Herschel's family may at no distant period " let the 

 world know more of the greatest of practical astro- 

 nomers" ... "of a great and ardent mind whose 

 achievements are and will remain the glory of England ;" 

 and in this connection, that whatever may be found 

 amongst his manuscripts (and as regards the drawings of 

 the nebulcB, no less an authority than the late Prof. 

 D' Arrest has expressed a strong hope of further publica- 

 tion) may at the same time be given to the astronomical 

 public' 



J. R. Hind 



■ Prof. Holden's work is published in London by Messrs. W. H. Allen 



