NA TURE 



[November 3, 1904 



he got hold of a gardener to give him some practical 

 advice. However, with this slight drawback, the book 

 is admirably designed for the teacher who wishes to 

 work out an elementary course of instruction for a 

 country school, either as an introduction to practical 

 life or to a more special study of agriculture and horti- 

 culture. 



I. Clinical Lectures on Diseases of the Nervous 

 System. Pp. 279; price ys. 6d. II. Lectures on 

 Diseases of the Nervous System. Second series. 

 Pp. 250 ; price 6s. net. By Sir William R. Gowers, 

 M.D., F.R.C.P., F.R.S. (London: J. and A. 

 Churchill, 1895 and 1904.) 

 In these two volumes Sir William Gowers has collected 

 in revised form a number of clinical lectures which 

 have appeared in various medical journals. In the 

 latter volume he has also printed the Bowman lecture 

 on subjective visual sensations delivered to the 

 Ophthalmological Society, and the Bradshaw lecture 

 on the subjective sensations of sound. The clinical 

 lectures deal with many subjects in neurology; some 

 are mainly descriptive, some speculative. In reading 

 them one not only appreciates the original and 

 suggestive way in which the facts are presented, but 

 also the finished literary style. In a short notice it is 

 impossible to deal with them in detail. The two 

 lectures on the subjective sensations of vision and hear- 

 ing are perhaps of wider scientific interest than the 

 clinical lectures. In the first the visual phenomena 

 experienced by sufferers from migraine are described 

 and figured, and there is an admirable resumd of 

 physiological teaching with reference to vision. In 

 the second lecture the phenomena of tinnitus, of 

 auditory vertigo, and other labyrinthine sensations are 

 discussed in a luminous and attractive way. Both 

 neurologists and physiologists will find much in these 

 volumes to assist and to stimulate them in researches 

 into nervous phenomena. 



Lectures Scientifiques. A French Reader for Science 

 Students containing Extracts from Modern French 

 Scientific works in Chemistry, Physics, Mathematics, 

 Physiologv and Botany, with a Glossary of Technical 

 Terms. "'By W. G. "Hartog, B.A. Pp. vii + 371. 

 (London : Rivingtons, 1904.) Price 55. 

 'The University of London now insists that candidates 

 for a degree in science shall be able to read and under- 

 stand accounts in the original of French and German 

 scientific work. In compiling this book Mr. Hartog 

 has had the needs of such students in mind so far as 

 French is concerned, and he has succeeded in bring- 

 ing together a varied and representative collection of 

 extracts from French scientific works and scientific 

 periodicals. Among the latter the Revue g^ndrale des 

 Sciences takes a very prominent position, contributing 

 to Mr. Hartog's collection as many as fifteen extracts. 

 The book should be of service not only to the under- 

 graduates referred to, but also to students of science 

 everywhere, for it is now more than ever necessary that 

 the man of science should be able to acquaint himself 

 at first hand with the results of fellow-workers abroad. 

 L'Industrie oliicole (Fabrication de I'Huile d'OJive). 

 By J. Dugast. Pp. 176. (Paris : Gauthier-Villars 

 and Masson et Cie., n.d.) Price 3 francs. 

 'This little volume, which belongs to the Aide-M^moire 

 series, is a practical account of the manufacture of 

 olive oil, and indicates several directions in which the 

 results of scientific research have been utilised to im- 

 prove technical processes. The formation and compo- 

 sition of olives are first explained, then the methods of 

 extracting the oil are described and an account given 

 of the appliances necessary for the purpose. The 

 properties and methods of preservation of olive oil and 

 the utilisation of the oil-cake are also considered. 

 NO. 1827, VOL. 71] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by bis correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for ttiis or any other part of Nature. 

 No notice is taken of anonymous communications. \ 



A Note on the Coloration of Spiders. 



It is well known that in a large number of animals, both 

 vertebrate and invertebrate, the colour of the flanks and 

 ventral side of the body differs from that of the dorsal. In 

 the majority of cases the dorsal surface is most darkly 

 tinted, the ventral palest, and the flanks intermediate in 

 depth of tone between these two. This gradation of colour- 

 ing has the effect of neutralising the shadows that are cast 

 by the upper upon the lower portions of the body. Thus the 

 animal does not stand out in prominent relief, but is, so to 

 speak, artistically flattened, and thereby rendered less 

 conspicuous. 



To this general rule I have recently observed an interest- 

 ing exception which affords strong evidence in favour of 

 the truth of the above interpretation. The spiders belong- 

 ing to the genus Linyphia are, almost without exception, 

 darkly coloured upon the ventral surface ; their flanks are 

 variously slashed with oblique white bars and stripes, while 

 their dorsal surface is yet more freely speckled with white 

 or pale spots and lines. In these spiders, then, the scheme 

 of coloration is the exact opposite to that which prevails 

 elsewhere. Now the Linyphiidaj spin horizontal webs, in 

 the centre of which they rest inverted, clinging to the lower 

 side. Thus it is the ventral side of a Linyphia that is ex- 

 posed to the strongest light, the dorsal side being in the 

 deepest shadow. The inversion of attitude at once fully 

 explains the inverted shading of the body. 



Oswald H. Latter. 



Charterhouse, Godalming, October 30. 



Sir J. Eliot's Address at Cambridge. 



Against some of the main conclusions of Sir J. Eliot's 

 opening address before Section A (subsection : cosmical 

 physics) may be set the facts that south-east winds are rare 

 on the south-east coast of South Africa, and that the rain 

 of the greater part of the tableland and south-east coast 

 comes mostly from some northerly direction. 



My concern, however, is chiefly with the following re- 

 marks, reported in Nature of August 25 last : — 



" The chief features of the rainfall of the period 1895— 



1902, in the Indo-oceanic region were as follows : — .... 

 There was a marked tendency in each year for late com- 

 mencement and early withdrawal of the monsoon currents, 

 and for deficient rainfall throughout the whole season over 

 the greater part of India. These features were very pro- 

 nounced in the years iSg6, iSgq, and 1901. The most re- 

 markable feature of the period was that the region to the 

 south of the equator, including South and East Africa, 

 Mauritius, and Australia, was similarly affected. . . . Mr. 

 Hutchins, Conservator of Forests, Cape Town, states that 

 drought prevailed more or less persistently over the Karroo 

 region in South Africa from 1896 to 1903, and that cattle 

 and sheep perished by millions. He also states that the 

 drought extended to British Central Africa from 1898 to 



1903. The previous statements evidence the continuity, 

 extension, and intensity of the drought. . . . The preceding 

 statements have shown that variations of rainfall for pro- 

 longed periods similar in character have occurred, and may 

 hence occur again, over the very large area including the 

 Southern Asian peninsulas. East and South .Africa, 

 Australia, and perhaps the Indian Ocean. The abnormal 

 actions or conditions giving rise to these large and prolonged 

 variations must hence be persistent for long periods, and 

 be effective over the whole of that extensive area." 



Now the question is, what is a drought? From one 

 point of view there is nothing but drought over a verv laro-e 

 area of South Africa. But I gather from the table you 

 print, showing the variation of the mean actual rainfall 

 from the normal in India, that by drought is meant unusual 

 and prolonged general dryness setting up marked economic 

 results such as " large loss of cattle and great loss of 



