December 26, 1912] 



NATURE 



461 



IVimblcdon Common: its Geology, Antiquities 



and Natural History. By Walter Johnson. 



Pp. 304. (London: T. Fisher Unwin, 1912.) 



Price 5s. net. 

 The natural history — using the term in its widest 

 sense — of any restricted area has a charm of its 

 own, though it may appeal but to a limited 

 number. A thorough study of the geology, anti- 

 quities and natural history of a district is a valu- 

 able piece of education, somewhat akin to the 

 .study of " types " in biology, and anyone who has 

 pursued such a course will have his interest stimu- 

 lated, and be in a far better position to enjoy the 

 charms of his own or of a foreign country than 

 had he not done so. 



The present book deals with Wimbledon 

 Common, a stretch of moorland and wooded 

 country, in the heart of which it is difficult to 

 realise that Whitehall is but half-a-dozen miles 

 or so distant. An interesting account is given of 

 the geology, botany and zoology of the district, 

 and the antiquarian and historical sides are well 

 dune. We have a personal acquaintance with the 

 common and can testify to the general accurac}' 

 of the book, and the perusal of it has added much 

 to our knowledge of the district. Mr. Johnson 

 expresses the hope that his chapters may be of 

 service in the cause of "nature study," and we 

 can cordially recommend it for such a purpose. 

 The book is well illustrated with a number of 

 plates and drawings and four maps. R. T. H. 

 'i elephotography. By C. F. Lan-Davis. Pp. xi 



- 130. (London : G. Routledge and Sons, Ltd., 



n.d.J Price zs. net. 

 The getting of a large enough image of distant 

 objects, or of near objects without an unpleasant 

 proximity to them, is a difficulty that often presents 

 itself to the photographer. A lens of greater focal 

 length is theoretically serviceable in such cases, 

 but the long camera that it would require may 

 not be available, and if provided would often be 

 troublesome to manipulate. This accounts for the 

 popularity of telephotographic lenses. Some of 

 them have the positive and negative elements fixed 

 with regard to each other, and then they differ 

 little, if at all, in their use from lenses of the 

 ordinary simple type. But when the two elements 

 are adjustable with regard to each other, in order 

 to allow of obtaining various sizes of the image, 

 manv new problems arise. W'e therefore welcome 

 this little volume, in which these problems are dealt 

 with in a practical and very concise manner. 



The book includes some remarkable illustra- 

 tions, such as a photograph of Mount Kenya, in 

 British East ."Xfrica, taken from a distance of 

 ninety miles, while at the other extreme as to 

 distance is a photograph of an Emperor moth 

 about life size. A short chapter on "telephoto- 

 micrography " deals with an application of these 

 lenses that is too often neglected. The 

 magnification conveniently obtainable \\ith instru- 

 ments at present on the market is ahvays very 

 low, the advantage being in the greater distance 

 between the lens and the object, which improves 

 the perspective and facilitates the lighting. 

 NO. 2252, VOL. 90] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



The Natural Fracture of Flint. 



Sir E. li.'W Lankester, K.C.B., in his learned and 

 comprehensive article in Nature of November 21, has 

 suggested the various lines of research which it will 

 bo necessary to follow if a thorough-going knowledge 

 of the mode of origin, structure, and fracture of flint 

 is to be obtained. 



The first two, which are intimately associated with 

 the sciences of chemistry and physics, I am, owing 

 to a lack of knowledge of these subjects, unable to 

 deal with. But having for some time past carried out 

 a series of experiments with flints subjected to natural 

 percussion and pressure, I have been able to discover 

 certain facts which I think may interest prehistorians, 

 and help them to decide with more certainty what is 

 human flaking upon any given stone, and what is not. 



In order to provide conditions in which flints would 

 strike each other fortuitously, I could think of no 

 better plan than to get a large sack, and, placing 

 eight or nine stones in it, shake it violently about for 

 some considerable time, and afterwards observe 

 whether any of the flints had been flaked in the 

 process. 



For my experiments with pressure I used a con- 

 verted letterpress and a differential screw-press, with 

 which very considerable pressures were obtained. 



The rudimentary character of these appliances may 

 be used by some as an argument against the value 

 of the resuks obtained, but it seems to me that the 

 nature of a blow does not differ whether it is delivered 

 in my sack, or on a sea-beach, or in a fast-running river. 

 In the same manner, pressure is pressure, whether 

 applied in my presses or under a mass of gravel, ice, 

 or other weight of material. 



Moreover, I have noticed that stones found on sea- 

 beaches which have been flaked by the action of the 

 sea exhibit the same characteristics as those resulting 

 from mv sack experiment, and I think that the flaking 

 on my specimens will be found to be in accord with 

 that of any stones from any geological deposit which 

 can be proved to have been flaked by fortuitous blows 

 or pressure. 



I propose now to give a description of the flaked 

 specimens resulting from my experiments, and to show 

 how, in my opinion, they differ from flints found in 

 various pre-river-drift deposits, and which I and others 

 look upon as having been flaked by man. 



I will deal first with those chipped by fortuitous 

 blows in my sack experiment. 



(i) Flaking was produced upon stones which were 

 more or less of a wedge shape, the thinnest end of 

 the wedge being that from which the flakes were 

 removed. 



In the deposits which we examine we find that the 

 flaked flints are of all and every shape, and this leads 

 us to conclude that man has been the fracturing agent. 



(2) The large majority of the fortuitous flakes were 

 short and cut deeply into the stone, showing that the 

 blows which caused their removal had impinged almost 

 directlv upon the edcre itself. This opinion is sup- 

 ported by the fact that the edge is blunted where 

 blows have fallen upon it. 



The larce maiorify of the flakes which have been 

 removed from the stones considered to be human are, 

 in the first place, differently formed and longer, and 



