March 2, 1891,] 



KNOWLEDGE 



41 



^>* AN ILLUSTRATED '^«/ 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: MARCH 2, 1891. 



CONTENTS. 



On the Form of the Milky Way. By John Richard 



Sutton, B.A. Cantab 41 



Giant Birds. By R. Lvdekkkr. B.A.Cantab .. 43 



The Magic Square of Four. By T. Squire Barrett, F.S.S. 4.5 



A Perpetual Calendar ... 47 



Note on the Orbit of the Double Star 2 2. By S. VV. 



BURVIIAM ... ... ... ... ... ... ... ... 48 



Letter:— E. W. Maundeu 49 



The Milky Way In the Southern Hemisphere By A. 



C. Ranyard ... ... ... ... ... ... ... 50 



Notices of Books 51 



Birds and Berries. By the Rev. Alex. S. Wil.son, M.A., B.Sc. 52 



Variable Stars of the Algol Type. By Miss A. M. Ci.erke 53 



Notes from Cambridge. By R. B. Johnson 56 



Artificial Cold. By Vacghan Cornish, B.Sc, F.G.S. ... 56 



Whist Column. By Montagu Gattie, B.A.Oxon 58 



Chess Column. By C. D. Locook, B.A.Oxon. 59 



ON THE FORM OF THE MILKY WAY. 



By .John Richard Sutton, B.A.Cantab. 



THE late Mr. Proctor shone as a critic. One gets 

 the same impression from a literary review by him 

 as from one of Matthew Arnold's literary reviews, 

 viz. that in most cases common sense has little 

 more to say. His essays on the star-work of the 

 two Herschels are among the most masterly in the language, 

 and are destined, no doubt, to be read for generations. 

 But his original speculations are not always so happy. His 

 genius was iconoclastic rather than creative ; and although 

 few who have appreciated the significance of the work of 

 Michell and the school he set up will question the fact that 

 Proctor has successfully summed up, once for all, the case 

 against Sir William Herscliel's " cloven-llat-disc theory " 

 of the Milky Way, yet it is doubtful if the same success 

 can be claimed for the " spiral theory," which he advanced 

 as comprehending all the results of observation on the 

 stars and nebulas. 



It would be out of place here to enter into a discussion 

 of the stellar researches of the Herschels. It will be 

 sufKcient to say that the elder Ilerschel assumed the stars 

 to be, on the (iirrdi/c, scattered more or less uniformly 

 throughout the visible universe, and hence, by counting the 

 number of stars visible in any one direction, he was, as 

 he thought, able to arrive at a pretty fair approximation to 

 the depth of the star-system in that direction. [It is not 

 hard to see that when the telescope is ti.\ed on any point 



in the sky, the boundaries of vision trace out a cone in the 

 celestial sphere of which the eye is the vertex.] The 

 yoimger Herschel seems to have accepted his father's 

 results with little more than a twinge of doubt, although 

 it is not so certain that he placed a very great faith in the 

 trustworthiness of the star-gauging methods from which 

 they were derived ; for he could also see, brilliant 

 mathematician as he was, that Michell's application of 

 the doctrines of probability had practically set at rest the 

 fact that in in'iieml star-grouping was physical and real, 

 and not merely optical, and hence that the stars were by- 

 no means imiformly distributed. Still, the doctrine of 

 probabilities had not sufficient hold upon his mind to cause 

 him to give up the delightfully systematic results of star- 

 gauging, to say nothing of the paternal authority by 

 which the old theory was backed. 



Proctor, however, took higher ground. In his hands 

 Michell's researches were, so to speak, born again. The 

 star-groups were physical facts (which, indeed, Sir William 

 Herschel had never doubted, though he left it out of 

 account) ; the constellations were realities of association 

 (of which Sir William Herschel had never even dreamed) ; 

 immense streams of stars, physically connected inter sc, 

 were to be traced across the sky ; and, last of all, the 

 Milky Way itself was a great stream of stars" — and not a 

 solid disc — to which all the other streams and groups were 

 subordinate. These different conclusions were advanced 

 from time to time for many years, and, taken together, 

 they comprise an analysis of stellar phenomena whose 

 immense value cannot be denied. 



It would be an agreeable task for me to give here, as 

 far as possible, an account of Proctor's very successful 

 work among the stars. But such a course is just now out 

 of the question ; moreover, most readers whom this 

 paper may concern will have read his original papers. I 

 shall content myself by remarking that he veiy early con- 

 cluded that all available evidence pointed in one direction, 

 namely, that the characteristic feature of our universe, 

 the Milky Way, was one long stream of stars of a spiral 

 form, whose plane passed very nearly through the sun's 

 place. He says : "It is very clear what views we are to 

 form respecting the Milky Way. If the galaxy is, lirst, a 

 clustering aggregation separated from us by an interval 

 comparatively clear of small stars ; sirondh/, so shaped 

 that the cross-section of the stream is everywhere not far 

 from a roughly circular figure ; and, thirdlij, associated 



* Sir William Heischel's language, even in his early papers of 

 1784 and 1785, and much more in his later papers on the Construc- 

 tion of Heavens, published in the Phil. Trans, of 1802 and 1811, 

 clearly prove that ho fully appreciated the fact that there are actual 

 clusters and streams of stars, as well as vacant spaces, in the 

 heavens. It is evident, also, that he recognized the connection 

 between the di.stribution of stars and the distribution of nebul.t. As 

 early as 1802 Sir W. llerschel's language clearly shows that he con- 

 sidered the Milky Way to be a roughly circular ring-shaped region, 

 in which the stars are more thickly grouped than in the space im- 

 mediately around the sun. He says, in a pap^r published in the P'lil. 

 Trims, in 1802: "The stars we consider as insulated are also 

 surrounded by a magnificent collection of innumerable stars, called 

 the Milky Way, which must occasion a very powerful balance of 

 opposite attractions to hold the intermediate stars in a stite of rest. 

 For though our sun. and all the stars we see, may truly be said to be 

 in the plane of the Milky Way, yet I am convinced, by a long inspec- 

 tion and continued examination of it, that the Milky Way itself con- 

 sists of stars very differently scattered from those which are 

 immediately about us." Sir John Herschel also clearly recognized 

 the close clustering of stars in the region of the Milky Way. Mr. 

 Proctor was well aware that both the Herschels had recognized the 

 existence of star-streams as well as groups of nebul:e. But I agree 

 with Mr. Sutton that neither Sir William nor Sir John Herschel pro- 

 ceeded to the conclusion which should have logically followed. 

 namely, that their method of star-gauging could not be relied upon 

 for determining the form of the stellar universe. — A. C. Ranyaru. 



