8 



KNOWLEDGE 



[January 1, 1895. 



the iuniper and the holly may be found in many places on 

 the chalk soils growing indigenously, and a really primjeval 

 forest of these trees may be seen to-day so near London 

 as the slopes of Eiddlesdown, at Kenley. 



From the very absorbent character of chalk the Downs 

 form, speaking generally, a streamless area, except after 

 unusually wet seasons, when a few streams flow for a time, 

 the result of the plane of supersaturation of the chalk 

 rismg above valley bottoms. The Kenley Bourne is perhaps 

 the most noteworthy of these intermittent streams. The 

 following are summit levels along the Surrey l)owns from 

 west to east : — The Hog's Back, 503 feet ; Albury Down, 

 62o feet ; nietley Heath, 674 feet; White Downs, 723 feet ; 

 Box Hill, 644 feet; Headley Heath, 619 feet; r.uokland 

 Hills, 708 feet ; C^olley Hill, 732 feet : Eeigate Hill, 762 

 feet ; Gravelley Hill, 777 feet ; Tandridge Hill, 791 feet ; 

 Woldingham Down, 816 feet ; Botley Hill. 881 feet. 



The Chalk forming the North Downs, dipping as it does 

 to tiie north and cut oif abruptly on the south, is obviously 

 but the northern remnant of a great sheet which extended 

 across the entire Wealden area, and was continuous with 

 the Chalk of the South Downs that dips in the opposite 

 direction. The geological structure of the entire district 

 gives an east and west main anticlinal through the middle 

 of the Weald, throwing off the upper beds to the north 

 and the south, and giving a great denuded surface of lower 

 beds forming a central area. 



North of the Downs lies the undulating and well-wooded 

 area that is bordered by the Thames, and watered by the 

 Wey, the Mole, the Hog's Mill iiiver, the Beverley Brook 

 and the Wandle. Some of this area near the Thames 

 is very low, but it rises to 184 feet above Ordnance Datum 

 at Richmond Hill, to 296 feet at Streatham Common, and 

 to 379 feet at the Crystal Palace. 



This is the Lower Eocene area of Surrey, and with the 

 Bagshot district forms the Surrey portion of the London 

 Tertiary Basin. The London Clay forms the great bulk of 

 the area, the Woolwich Beds giving but a small breadth of 

 land and the Oldhaven Beds a still smaller acreage, while 

 the Thanet Sands have a very inconsiderable outcrop. At 

 the lower levels, however, river gravels and brick-earths 

 largely cover the London Clay, and bordering the Thames, 

 the Wey and the Mole there are strips of Alluvium. 

 Gravels over the Loudon Clay form the surface at higher 

 levels, as at Clapbam, Wimbledon, and other commons, 

 and even on the Norwood Hills there are patches of these 

 superficial deposits. 



From this varied geological structure of Surrey, hills and 

 vales, level stretches and picturesque highlands, rich 

 woods and smooth and swelling downs, parks and wastes, 

 highly-cultured fertile lands and barren heaths, all combine 

 to form this beautiful southern county, while, flowing 

 through a world-renowned vale, the silver Thames winds 

 for fifty miles along its northern side. 



We read in Cnssier's irni/tiziiie that the smallest 

 generator of electrical or mechanical energy in the world 

 is a battery constructed by one of the electricians of the 

 Boston Telephone Company, consisting of an ordinary 

 glass head, through which two wires, one of copper and 

 the other of iron, are looped and twisted so as to prevent 

 their coming in contact. The wires act as electrodes, and 

 a drop of acidulated water in the head causes a current to 

 flow. It has been used in signalling to a distance of 

 nearly two hundred mUes. 



■\." The picture of "The Spider's Web" in the December 

 number of Knowled(;e was taken from a photograph kindly 

 supplied by the Eev. H. D. Nicholson, of Tavistock. 



It is with the deepest regret that we have to 

 announce the death of Mr. Arthur Cowpek Eanyaki>, 

 the Editor of Knowledge. Mr. EANr.\Bi) died at 

 his residence in Bloomsbury, on Friday evening, 

 December 14th, 1894. 



THE CONSTRUCTION OF THE VISIBLE 

 UNIVERSE. 



By .J. E. Gore, F.E.A.S. 



AN examination of the evidence we have at present, 

 with reference to the distribution of the visible 

 stars in space, has recently been undertaken 

 by Prof. Kapteyn of Grouingen, and a popular 

 account of the conclusions he has arrived at may 

 prove of interest to the general reader. 



It must first be explained that, in order to obtain a clear 

 view of the construction of the visible heavens, it would be 

 necessary to know the relative distances of a large number 

 of stars ; but as the distances of only a few stars have 

 yet been determined, and the results hitherto obtained are 

 open to much uncertainty, we must have recourse to some 

 other method of estimating these distances. In travelling 

 in a railway carriage, if we fix our attention on the trees, 

 buildings, and other objects we pass on our journey, it will 

 be noticed that all objects apparently move past in the 

 opposite direction to that in which we are travelling, and 

 that the nearer the object is the faster it seems to move 

 with reference to distant objects near the horizon. So it 

 is with the stars. The sun is moving through spape, 

 carrying along with it the earth and all the planets, 

 satellites, and comets forming the solar system. The efl'ect 

 of this motion is to cause an apparent small motion of the 

 stars in the opposite direction, and the nearer the star is 

 tD the earth the greater will this apparent motion seem to 

 be — as in the case of the railway train. In addition to 

 this apparent motion, the stars are themselves — hke the 

 sun — moving through space, and this iral motion is also 

 visible. If this real motion takes place in the opposite 

 direction to that in which the earth is moving it will add 

 to the apparent motion, and will increase the " proper 

 motion," as it is termed. If, on the other hand, the real 

 motion is in the same direction as the earth's motion, it 

 will tend to diminish the proper motion. In either case, 

 the nearer the star is to the earth the greater will be its 

 apparent annual displacement on the background of the 

 heavens. The amount of the "proper motion" is, there- 

 fore, considered by astronomers to form a reliable criterion 

 of the star's distance from the earth, and the actual 

 measures of distance which have been made show that this 

 assumption is approximately true. Of fourteen stars which 

 have a proper motion of over three seconds of arc per 

 annum, eleven have yielded a measurable parallax, or 

 displacement due to the earth's annual motion round the 

 sun — that is to say that eleven out of fourteen fast-moving 

 stars are within a measurable distance of the earth, and 

 therefore near us when compared with the great majority 

 of the stars which are not within measurable distance, or, 

 at least, are beyond the reach of our present methods of 

 measurement. 



In the case of small groups of stars, we may assume 

 that the real motions of the individual stars take place 



