56 



NA TURE 



[May 2 



903 



is known to exist, and contrasting the results with those 

 obtained elsewhere with the same instruments. 



Prof. Milne mentions Kew and Greenwich as representa- 

 tives of stations where magnetic and gravitational anomalies 

 do not exist, but, as a matter of fact, Rucker and Thorpe's 

 magnetic survey does show a small magnetic anomaly in 

 the Thames Valley, and certain foreign observers have also 

 inferred a gravitational anomaly. 



As to Prof. Milne's special term " geite " for material in 

 the earth's interior, I must confess that the application of a 

 new word to the unknown material of a problematical core 

 seems to me more likely to hinder than assist. Such special 

 terms constitute an additional obstacle in the way of those 

 who are not specialists. Also existing terms, such as 

 nucleus and core on the one hand, and layer or crust on the 

 other, seem not inadequate, the context showing whether 

 it is the material that is immediately in view. 



I have had repeated occasion to deal with elastic problems 

 involving a core and a layer or layers. In fact, the very 

 *' earth " for which Prof. Milne expresses a preference, 

 consisting of a layer of about 1/20 of the earth's radius in 

 thickness with a density of average surface rock, and a 

 core of specific gravity approaching 6, is one which I 

 selected some years ago for the purpose of investigating 

 luni-solar tidal action (Cambridge Phil. Trans., vol. xvi. 

 p. 151). Thus I do not speak without experience. 



A final point to be remembered is that, according to the 

 investigations of Gauss and others, the earth itself is a 

 magnet of considerable moment. Any theory which claims 

 even provisional acceptance may be expected to give a 

 plausible explanation of this fact, and of the secular change 

 observed in terrestrial magnetism. C. Chree. 



Photograph of Oscillatory Electric Spark. 



The enclosed photograph of an oscillatory electric spark, 

 like most of those which I have taken, differs in some 

 respects, so far as I have seen, from those which have 

 been recorded by other experimenters. It was obtained by 

 the discharge of 22 square feet of coated surface through 



Fig. I. — Oscillatory electric spark. 



J mile of coiled wire, the electrodes being of magnesium. 

 The picture was focused on a circular plate fixed on the 

 end of an electric motor, so as to revolve in its own plane. 

 The number of double oscillations was about 3000 per 

 second. C. J. Watson. 



Bottville Road, Acocks Green, Birmingham. 



Our Rainfall in Relation to Bruckner's Cyfle. 



In the instructive paper on solar and meteorological 

 changes in Nature (May 7), I observe that Dr. Lockyer 

 suggests 1913 as probably about the centre of the next wet 

 period. A consideration of barometric changes appears to 

 lead to a similar result, and I may be permitted to recall 

 a letter sent you in 1898 (Nature, December 22, p. 175), in 

 which, discussing with such data the question, " Where do 

 we stand in Briickner's cycle? " I mentioned 191 1 as prob- 

 ably near that centre. Such estimates must, of course, be 

 regarded as merely approximate, and open to revision. 



This important cycle of Bruckner's was lately discussed 

 'in a number of letters to the Times, and it is satisfactory 



NO. 1 75 1, voL.^68] 



to see that more adequate attention is now, though tardily, 

 being given it. 



Is it not objectionable to treat the British Isles as a 

 whole, since, on Bruckner's theory, the western portion 

 shows opposite variation to the eastern? 



There is a method of curve-making which seems to be 

 little used by meteorologists, but which is, I think, to be 

 recommended. A series of annual rainfall figures (say) is 

 first translated into a series of plus and minus values (re- 

 lated to the average), and this series is then added alge- 

 braically step by step, e.g. 



+9-3-i-44-o-6-l-o-9-i-6-hi-3, &c. 

 +7-9+8S+9-4+7-8+9-I. &c. 

 This second series is then thrown into curve form. The 

 process is analogous to paying in money to a bank, and 

 drawing money out, and the point reached by the curve 

 at any given time indicates the balance. 



Each upward (annual) extension in such a curve repre- 

 sents a wet year, and each downward extension a dry year, 

 and the degree of wetness or dryness is also indicated. 



A large comparison of such curves for European and other 

 stations would, I think, throw a good deal of light on the 

 Bruckner theorv. Alex. B. MacDowall. 



The Propagation of Phthisis, 

 In a work called " Opera nuova intitulata il Perche, 

 utilissima ad intendere le cagioni de molte cose, &c.," 

 published in Venice in 1520, the following passage occurs :— 

 " Dal sputo del Tisico o da la sua boca viene fuora un 

 vapore fetido e acuto che entra poi per la boca de colui che 

 conversa con quello e corrode simelmente il pulmone de esso 

 e in questo modo genera tisica." 



Substitute for vapore " material particles," and we 

 have the modern conception of the mode of propagating 

 consumption. This anticipation of modern science seems 

 worthy of note. Edmund McClure. 



TANGANYIKA.' 



THE title of this work is perhaps somewhat mis- 

 leading. The reader who expects the book to 

 contain only discussions of speculative questions \yill 

 be agreeabl)' surprised by finding that the positive 

 contributions made in it to our knowledge of the 

 geology, botany and zoology of Central East Africa 

 are of the most extensive and valuable character. The 

 two expeditions which the author undertook in 1896 

 and 1899 to Lake Tanganyika and the surround- 

 ing districts, following upon the researches of earlier 

 travellers, have thrown a flood of light upon both the 

 geological structure and the fauna and flora of this 

 part of the world, while they have incidentally sug- 

 gested a number of diflficult problems of_ no small 

 interest alike to the geologist and the biologist. 



The surveys of Mr. Moore and of Mr. Malcolm 

 Ferguson, the geologist who accompanied him, have 

 been of value in rectifying and making noteworthy 

 additions to the maps of the area visited. The geo- 

 grapher will find references to a number of new moun- 

 tain peaks, the heights of many of which are given, 

 with the determination of the heights above sea-level 

 and the depths of many of the lakes, in several of 

 which numerous soundings and dredgings were made. 



One of the most valuable results of Mr. Moore's 

 explorations is the confirmation he is able to supply 

 to the conclusions of Mr. Scott Elliot that there exists 

 in East Central Africa a great mountain chain running 

 north and south, and rising at many points, even in 

 this Equatorial region, above the limits of perpetual 

 snow. The height of the snow-line is fixed by Mr. 



1 " The T.iiiganvika Problem ; an Account of the Researches undertaken 

 Concerning the Existence of Marine Animals in Central Africa." By 

 T. E. S. Moore, F.R.G.S., author of " To the Mountams of the Moon 

 Pp. xxiii + 371 ; with 7 maps and 140 illustrations. (London : Hurst and 

 Blackett, Ltd., 1903.) 



