Oct. 1 8, 1877] 



NATURE 



519 



ments), but in other cases (including tlie tones of the 

 siren, and the human voice) it depends on a very different 

 cause, namely, the mathematical law that every series of 

 precisely similar vibrations is cither simple, or com- 

 pounded of one set of simple vibrations, giving the 

 fundamental tone, and other sets of simple vibrations 

 giving the harmonics." Now the second cause — Fourier's 

 law — is surely the only one for the existence of harmonics, 

 and in every vibration, whether of a string or any other 

 body, the ear analyses the motion of the air in accordance 

 with the law, that is, hears harmonics. Is it possible 

 that the origin of the misconception here lies in 

 the old notion that when a string vibrates in any 

 regular manner there are secondary waves riding on the 

 primary ones, another set on these secondary, and so 

 on .' as — 



" Great fleas have little fleas 



Upon their backs to bite 'em, \ 



The little fleas have lesser fleas, 



And so ad infinitum." 



By the way, why are the notes of the human voice, 

 which are produced by the vibrations of the vocal chords, 

 distinguished from the notes of stringed instruments ? 



It is not to be expected in an elementary manual that 

 every subject, even of importance, should be noticed, but 

 we should have thought that even in the briefest treatise on 

 heat, some notice would have been taken of the " theory of 

 exchanges," and yet we find no mention whatever made of it- 

 Also a little more space than two pages might have been 

 devoted to the electric telegraph, especially, first, as room 

 has already been found for the description of the venerable 

 three kinds of lever, and the antiquated three systems of 

 pulleys (which are rarely seen except in [text-books of 

 physics) ; and, secondly, inasmuch as three times the 

 space is taken up in the description of the air-pump and 

 its modifications. 



The good qualities of the book are so conspicuous, and 

 its faults either so slight or so easily corrected by the 

 teacher, that we have no hesitation in warmly recom- 

 mending it as a good text-book for junior classes. 



T. H. C. 



OUR BOOK SHELF 



Popular British Fnn^i; containing Descriptions and 

 Histories of the Principal Fungi, botli Edible and 

 Poisonous, of our Country. Illustrated. By James 

 Britten, F.L.S. (London: the Airasr Office.) 



This admirable little book forms an agreeable and 

 popular introduction to a much neglected group of plants. 

 Written in a pleasant easy style, it yet conveys a great 

 deal of sound information. Mr. Britten having drawn on 

 his imajiination merely for the setting of his facts, not for 

 the facts themselves. The different illustrations convey 

 a tolerably accurate idea of the plants represented. The 

 edible fungi are carefully described, and most useful hints 

 and directions given as to the modes of cooking and 

 preparing for table. The poisonous forms also receive a 

 considerable share of attention, and the characters are 

 carefully given, but even with all sorts of descriptions we 

 cannot but think that there is alwa) s danger from such 

 genera as Lactarius and Russula. Besides treating cf 

 the usual edible and poisonous fungi, Mr. Britten gives 

 a chapter on Dry Rot, another on Luminous Fungi, and 

 another on the Sphaeriacci. Throughout the whole book 

 we constantly meet with quaint quotations from old 

 authors. The book, then, is not only a very pleasant and 



readable one, but conveys a great deal of sound informa- 

 tion on the subject therein treated. 



Zeitscltrift fUr das chcniische Grossgewcrbc. Heraus- 

 gegeben von Jul. Post. II. Jahrgang. Heft I. 

 (Berlin : Robt. Oppenheim.) 

 We have already had occasion to express our high opinion 

 of the value of Dr. Post's contributions to chemical techno- 

 logy. The present work is to the chemical manufacturer 

 what the well-known '' Jahresbericht " of Liebig and Kopp 

 is to the scientific chemist. It attempts to give the tech- 

 nologist a systematic account of the latest advances in 

 the several departments of manufacturing chemistry and 

 the allied arts. As the various contributions are from 

 the pens of men who, in the majority of cases, have 

 made the matters upon which they write the objects 

 of special attention and study, we can confidently re- 

 commend the work to the notice of our chemical 

 manufacturers. 



LETTERS TO THE EDITOR 



\The Editor does not hold himself responsible for opinions expressed 

 by his correspondettts. Neither can he undeitake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 



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 otherwise to ensure the appMrance even of com- 

 t/mnicaiions containing interesting and novel facts, '\ 



Indian Rainfall Statistics 



Several correspondents in the Times and elsewhere have 

 lately complained regarding the class of information furnished 

 by the Government of India with reference to the famine. One 

 of them pointed out that while the Indian official Gazette is filled 

 with tables of food-prices, and other statistics, there seems to be 

 no attempt to deduce the real significance of those figures, nor 

 are any data of comparison offered by which the public might 

 make deductions for themselves. I have just come across a very 

 glaring instance of this. The Indian rainfall havmg been dis- 

 cussed a good deal this summer in yoar columns, I heard with 

 some rejoicing that a long list of returns had been given in the 

 Indian Gazette for stations in Madras and Bombay. The returns 

 purport to bear upon the variation of rainfall in tropical India 

 with reference to the cycle of sun-spots. As an old resident in 

 Madras and Hyderabad, I think it would be difficult to produce 

 a series ol figures more irrelevant or more misleading with regard 

 ii the matter in hand. So far as I understand your articles, it 

 s alleged that of the six famines in Southern India since 1810, 

 five were caused by great droughts at tlie periods of minimum 

 sun-spot frequency. It also seems to be alleged by you that the 

 rainfall at Madras itself follows a cycle curiously coincident with 

 the eleven-year cycle of sun-spots. These are two propositions 

 distinct in themselves, and either of them is well worthy of 

 investigation by the Meteorological Reporter to the Government 

 of India. 



The figures signed by that ofiicer in the Gazette yield no infor- 

 mation on the subject. He begins by completely mis-stating the 

 case. Instead of testing the one statement as to whether drought 

 and famine in Southern India have been coincident with periods of 

 minimum sun-spots, or the other statement as to whether the 

 rainfall at Madras itself forms a cycle coincident with the sun-spot 

 cycle, he assumes that the question at issue is whether the rainfall 

 at all the stations throughout Southern India shows a common 

 periodicity coincident with the cycle of sun-spots. 



Now, sir, it surely displays a gross ignorance with regard to 

 the geographical facts of Southern India, to suppose that a 

 periodicity, or any other feature of the rainfall of a place on the 

 coast, like Madras, can be reproduced at the stations which the 

 paper seems to take haphazard at the inner recesses beyond the 

 Ghauts. I shall take, for example, only three stations in which 

 I have resided, and whose monsoons I have seen. Madras 

 derives about two-thirds, or twenty-nine inches, of its total rain- 

 fall from the north-eastein monsoon between October and De- 

 cember. The periodicity of its total annual rainfall is chiefly 

 due to this monsoon. The Calcutta meteorological reporter 

 compares this station with Secunderabad, where the north- 



