July 28, 1887] 



NA TURE 



293 



technical points of view, and as regards the latter the 

 information hris been brought up to date by including 

 notices of Webster's improvements in the Ueville process, 

 Messrs. Cowles Brothers' electrolytic method of produc- 

 ing aluminium alloys, and the Castner process of reducing 

 sodium from caustic soda at a low temperature, which, in 

 conjunction with Webster's processes, seems likely to 

 render the production of cheap aluminium commercially 

 possible. 



The author has contributed to the appendix a series of 

 experiments made by himself on the formation and reduc- 

 tion of aluminium sulphide, which are of interest, although 

 the results, in the reduction experiments at any rate, 

 appear to have been mainly negative. Iron, tin, copper, 

 and antimony were employed as reducing agents, but 

 only with the first two metals was any reduction effected. 

 The concluding paragraph, therefore, reads rather oddly : — 

 " These processes have been covered by patents, but have 

 never been made successful. It appears that if rightly 

 managed they will give good results and produce alu- 

 minium alloys cheaply." 



Questions on Physics. By Sydney Young, D.Sc, F.C.S., 

 Lecturer on Chemistry, and Tutorial Lecturer on 

 Physics in the University College, Bristol. (London : 

 Rivingtons, 1887.) 



Assuming that books consisting of a series of questions 

 with their answers collected together at the end supply a 

 legitimate want and do a real service in the cause of 

 scientific education. Dr. Young's "Questions on Physics" 

 is a valuable addition to those already existing. It is as 

 free as it is possible to make such a book from the charge of 

 encouraging " cram," as the questions are many of them 

 not adapted to rule-of-thumb methods of solution. Many 

 of them also are descriptive of some instrument or prin- 

 ciple, in which case, of course, answers are not given. 

 The author takes in succession mechanics, acoustics, 

 heat, magnetism, electricity, and optics. After the 

 answers he gives a series of tables which will be found 

 useful. There are no questions on moment of inertia, or 

 on the ballistic galvanometer. One sentence — the last 

 part of question 155 — may vex the student: "Calculate 

 the focal length of a concave lens which gives a magni- 

 fication of three diameters at a distance of three 

 inches." 



The book is intended for the intermediate examination 

 in science and preliminary scientific examination of the 

 London University. 



Eminent Naturalists. By Thomas Greenwood, F.R.G.S. 

 (London : Simpkin, Marshall, and Co., 1886.) 



This is a little book (200 small 8vo pages) intended, as 

 the preface says, to furnish " short yet comprehensive 

 sketches of some leading naturalists." The sketches are 

 certainly " short," but can only be said to be " compre- 

 hensive" in the sense that this term may be applied to 

 an epitaph. It is difficult to understand what object such 

 very sketchy biographical sketches can be supposed to 

 serve. Moreover, in this case the subjects appear to have 

 been selected at random ; the result being that the por- 

 trait gallery, such as it is, presents a somewhat incon- 

 gruous assemblage— to wit, Linnaeus, Lubbock, Thomas 

 Edward, Louis Agassiz, Cuvier, Buffon, Lyell, and Mur- 

 chison. Whether this curious arrangement is intended 

 to express the writer's idea of the order of merit of these 

 men, or whether, like his choice of naturalists, it is purely 

 haphazard, we are not informed. But surely, if a bio- 

 grapher goes back as far as Linnaeus for his material, 

 and carries down his survey to the present generation, 

 even the most popular of popular readers might have 

 expected him to supply a less deficient index of " eminent 

 naturalists." 



LETTERS TO THE EDITOR. 



[The Editor does not hold himselj responsible for opinions 

 expressed by his correspondents. Neither can he under- 

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

 rejected manuscripts. Mo notice is taken of anonymous 

 com m un ic at ions. 



[ The Editor urgently requests correspondents to keep their 

 letters as short as possible. The pressure on his space 

 is so great that it is impossible othenvise to insure the 

 appearance even of comtnunications containing interesting 

 and novel facts.'] 



The Carnatic Rainfall. 



If I have rightly interpreted General Strachey's courteous 

 criticism of my paper on the Carnatic rainfall, the gist of his 

 objections may be summed up by saying that the method by 

 which I endeavoured to estimate numerically the genuineness of 

 the apparent cyclical variation of that rainfall, as a recurrent phe- 

 nomenon, is logically invalid. This, I must frankly admit, is 

 really the case ; my error has been somewhat of the nature of a 

 petitio principii, and is indefensible. I have reasoned upon a 

 series of values directly obtained from the observations, as if 

 they had been obtained deductively from some independent 

 source, and had been found, on trial, to agree, within certain 

 allowable limits, with the results of the observations. This pro- 

 cedure, as General Strachey has shown, is manifestly illogical ; 

 and the inferred "high probability that the apparent undecen- 

 nial fluctuation of the Carnatic rainfall is no chance phenome- 

 non," in so far as this conclusion depends on the above erroneous 

 reasoning, necessarily falls to the ground. But only in so far. 

 The validity of the data afforded by the registers remains, of 

 course, unaffected ; and these data, as they stand, seem to me 

 to furnish evidence of so pronounced a character that it is at 

 least improbable that the apparent fluctuation is fortuitous. The 

 considerations on which I base this opinion are : — 



(i) That each series of eleven years, taken separately, shows 

 a dominant fluctuation of that period, and these fluctuations 

 show much accordance, both in their ranges and in the epochs 

 of their critical phases. Simple inspection of the tabulated 

 annual means is sufficient to convince one that there is no regu- 

 lar fluctuation of anything like the same magnitude, differing 

 much from the eleven -year period. 



(2) The range of the fluctuation as educed by the harmonic 

 formula (restricted to two periodical terms), is four times as 

 great as the mean deviation of the recorded amounts from the 

 corresponding computed values. And this fact fulfils a condition 

 which, in a less rigorous form, General Strachey suggested, I 

 believe,^ as a test in his discussion of the Madras rainfall registers, 

 communicated to the Royal Society in May 1877, and the 

 failure of which he rightly assigned as a reason for doubtinsj the 

 reality of the supposed cyclical fluctuation of the Madras 

 rainfall. 



That the second of these considerations is valid has been 

 established in my former communication. The computed range 

 of the fluctuation was shown to be 14 inches, and the mean 

 annual deviation of the observed from the computed values 

 ± 3"5 inches. To render the first more obvious, I have com- 

 puted the harmonic constants, separately, from each of the two 

 undecennial series, and therefrom the annual values in each 

 case. The constants are : — 



ist Cycle. 

 «' = 7*23 ... u" = o"66 

 U' = 190° 16' ... U" = 322° 10' 



and the computed annual values — 



1864 

 1865 

 1866 

 1867 

 1868 

 1869 

 1870 

 1871 

 1872 

 1873 

 1874 



ist Cycle. 



Inches. 



- 170 



- 4"62 



- 6-35 



- 662 



- 4-99 



- I 39 

 -1- 3-i8 

 ■V 679 

 + 7-^3 

 -I- 5'8i 



H- 2-12 



' I quote from memory, not having the Proc. Roy. Soc. at hand. 



