52 



KNOWLEDGE 



[January 1, 1890. 



near Livtipool. \\'ith this 15-mch Bond also discovered 

 the cruiie, or dark ring of Saturn, on the 11th Xovember 

 1850 ; a discovery which was also duplicated iu England, 

 Mr. Dawes having observed it independently, before the 

 news arrived iu England, on the '29th of November. 



For fifteen years the twin 15-inch telescopes of St. 

 Petersburg and Harvard, both made by the same German 

 maker, remained the largest refracting telescopes in 

 existence. It was m America that the next step in ad- 

 vance was made by Alvan Clark, a portrait painter of 

 Cambridgeport near to Harvard, who iu 1862 made an 

 excellent 18-iuch refractor for the University of Mississijjpi. 

 With it, before it was quite completed, Alvan Clark dis- 

 covered the now well known companion of Sirius on the 

 81st of January 1862. The Civil War troubles having 

 commenced, the telescope was never sent to its southern 

 destination ; but it has made its' mark in the history of 

 astronomy, for it fortunately fell into the hands of Mr. 

 Burnliam. It w^as purchased by a Cliicago millionaire, 

 who installed it iu a handsome observatory, which he 

 dedicated to the public in memory of his wife, whose 

 maiden name was Dearborne. With this 18-inch iu the 

 Dearborne Observatory, Mr. Burnham discovered nearly a 

 thousand new close double stars. 



^^■ith the old 15 -inch refiactor of the Harvard Obser- 

 vatory Bond made his great di-awiug of the Orion Nebula 

 and his important observations of the comet of 1861. 

 Under Prof. E. C. Pickering's directorship the Harvard 

 Observatory has been considerably enlarged. The work 

 involved by his photometric and spectroscopic surveys of 

 the Heavens requires a considerable addition to the staff of 

 observers and computers. The additional expense in- 

 volved is pro^•ided for by the guarantees of private indi- 

 ^'iduals and voluntary subscriptions, a system which is 

 more likely to be fruitful of beneficial results than the 

 European plan of Government endowment, as it interests 

 a large number of people in the work carried on, and 

 their mterest reacts beneficially upon the workers. 



ORBIT OF ALGOL. 



Some seven or eight years ago Prof. E. C. Pickering 

 showed that there was considerable probability that the 

 variation in the light of Algol was due to the periodical 

 transits of a dark companion across the face of the bright 

 star. He pointed out that the orbit of the bright star in 

 such a system might be determined by spectroscopic obser- 

 vations, even when the distance of the system is not 

 known. At a recent meeting of the Prussian Academy, 

 Prof. Vogel stated that he had obtained six good photo- 

 graphs of the spectrum of Algol, three taken before 

 minimum periods and three after. The three taken pre- 

 viously to the minimum periods show the lines decidedly 

 displaced towards the red end of the spectrum, and the 

 thi'ee taken after the minima show- a similar displacement 

 towards the blue end as compared with the lines iu the 

 solar spectrum. From careful measurements Prof. Vogel 

 makes the motion of approach and recession of the bright 

 star to be about equal and to amount to 27 mUes per 

 second. Assuming a circular orbit for the stars in a plane 

 passing thi-ough the earth. Prof. Yogel derives the follow- 

 ing elements for the system of Algol. 



Diameter of Algol 1,074,100 EngUsh miles. 



Diameter of the dark companion 810,600 ,, 



Distance of centres 3,269,000 ,, 



Speed of Algol iu its orbit ... 27 ,, 



Speed of the companion in its 



orbit ... ... ... 56 ,, 



He makes the mass of Algol Aths that of our sim. and 

 the mass of the companion |ths. This is on the assump- 



tion that the density of the two bodies is similar, and 

 that there is a central transit. If the dark body transited 

 above or below the centre of the luminous body, its rela- 

 .tive size would be larger. 



We regret to annoimce the death of Prof. Lorenzo 

 Respighi, Director of the Osservatorio Campidoglio, Rome. 

 He died on the 10th of December. By his death astro- 

 nomv loses a most acti\e worker and acute reasoner. 



Notices of 9Sooltd. 



Hamjistedd Hill : Its Stiucturc, Matrriiils. mid Siuljitiirin'/. 

 By Prof. J. LoG.^x Lobley, F.G.S. (Eoper and Drowley.) 

 Just as the modern student of history finds it necessary to 

 have monographs on special periods, the lover of nature is 

 glad of books dealing wdth the features of some small dis- 

 trict with which he may be familiar. The museum-haimt- 

 ing specialist wants systematic memou-s, mcludiug all the 

 species of some one group ; but tliei'e are many genuine 

 students who will also read with avidity works relating to 

 outdoor natural history, to the geological history of the 

 landscapes they admire, and on the occurrence and tUstri- 

 bution through these well-known scenes of favourite plants, 

 birds, or insects. It is to this auditory that Professor 

 Lobley's elegant little book on Hampstead Hill will appeal. 

 Matters topographical and archaeological ha\e been perhaps 

 too rigidly excluded. The greater part of the book, that 

 by Professor Lobley himself, is geological. The style is 

 simple, and the geological chapters wiD be readily compre- 

 hended by anyone. It is needless to say, to those who 

 know the writer's long and enthusiastic study of London 

 geology, that they are accurate in detail. It might have 

 been as w"ell to refer to the fact that Professor Prestwich 

 has recently proposed the separation of the sands of 

 Hampstead fi'om the main mass of those in the Bagshot 

 area luider the name '• London Sands," and in a new edi- 

 tion we trust we may be mdulged in a special chapter on 

 the inferences from the Kentish Town Well, the section of 

 which is given without comment on p. 61, and other deep 

 borings, as to the oldest known condition of our London 

 area. 



It is, we presume, too late in the day to lament that 

 local natural histories no longer have the irresponsibly 

 gossipy form of White's Selbornc, Knapp's Journal of a 

 Nfitumlist, or Lees' Botanical TMol,rr-()iit, but must per- 

 force be pervaded by the lists which rightly occupy so large 

 a space in the Proceedimis of local societies. In looking 

 through the latter part of the work now mider notice, 

 however, we are constantly asking, like Oliver Twist, for 

 more. Mr. Harting's list of the birds of Hampstead has 

 indeed admiral)le, though brief, notes as to the frequency 

 and mode of occurrence of the several species ; but for the 

 flora and insect-fauna, contributed by Dr. Wharton and 

 the Rev. Dr. Walker, we have merely the bare lists. 



We could hardly imagine a work speakmg of the plants 

 of Hampstead without any reference to Thomas Johnson. 

 His Eriiitum HioiinU'dianum, published m 1G29, is the 

 second printed accoimt of a botanical excm'sion in Eng- 

 land, and his Enumeiatio plantarum in Ericeto Hain)i- 

 stediano rn'scintiuw , pubhshed iu 1632, and recording 111 

 species, is the first local flora printed in this country. 

 Then again Samuel Doody, who knew mosses "best of 

 any man," was buried at Hampstead on December 3, 

 1706, his funeral sermon being preached by Adam Buddie, 

 himseK one of the most accurate of botanists, and one 

 who made Hampstead one of liis chief himting-groimds. 



