June 28, 1877] 



NA TURE 



161 



067? BOOK SHELF 



Researches on the Glacial Period. By P. Kropotkin. 

 First fascicule. S27 pages in Svo. With Maps and 

 Woodcuts in a separate brochure. {Memoirs of the 

 Russian Geographical Society, vol. vii., 1876.) 

 The book consists of two parts. The first is a detailed 

 account of a journey in Finland and a short visit to 

 Sweden, both made in 1S71 under the auspices of the 

 Russian Geographical Society, for the special purpose of 

 studying the glacial formations and the osar (eskers or 

 kames). The second part is an inquiry into the meaning 

 and value of various evidences of the glacial period — the 

 striation cf rocks, the forms of rocks and mountains, the 

 boulders, the loose deposits, and the moraines and osar. 

 Out of the seven chapters into which this part is divided 

 only the three first (sketch of the development of the 

 glacial theory, striation, and forms of mountains) appear 

 in this fascicule, and the two last (loose deposits and their 

 classification, moraines, and osar) are summarised at 

 length in an Appendix. 



The first fascicule is illustrated by a hypsometric map 

 of Finland (southei'n half) with all known osar shown 

 upon it ; by a map of the most interesting, esker Pun- 

 gaharju, five miles long; by to no other maps and sec- 

 tions of less importance ; by a section on a large scale of 

 the loose deposits along the Tavastehus-Helsingfors 

 Railway, and by ninety woodcuts, a large part of which 

 are sections of osar. 



The main conclusions as to the glaciation of Fin- 

 land are in accordance with those arrived at by 

 Messrs. Erdmann, Wiik, Helmersen, and Schmidt, viz., 

 that this low table-land, continuous along its north-western 

 and southern borders with two low and flat border- 

 ridges, was covered with an immense ice-sheet which, 

 creeping from Scandinavia, crossed the Gulf of Bothnia, 

 traversed Southern Finland in a direction south by east, 

 crossed the Gulf of Finland and crept further on in the 

 Baltic provinces. The numberless stria;, the positions 

 and directions of which exclude any suspicion of their 

 having been traced by floating ice, the striation on the 

 islands of the shallow gulfs, together with that of the 

 Onega basin, the Neva valley, and the Baltic provinces, 

 the uninterrupted sheet of till, i.e., of a true unstratified 

 and unwashed morainic deposit covering Finland, the 

 numberless moraines parallel to the glacial stria;, and 

 hundreds of other evidences, settle the existence of such 

 an ice-sheet beyond any doubt. As to traces of marine 

 formations, there are none above a level of about 100 to 

 120 feet; only local lacustrine deposits cover the till 

 above this level. 



LETTERS TO THE EDITOR 



\_7he Editor does not hold himself responsible for opinicns expressed 

 by his correspondents. Neither can lie undertake to return, 

 or to correspond luith tlie writers of, rejected vianuscrit>ts. 

 No notice is taken of anonymous communications. 



T/ie Hdttor urf^ently retjuats correspondents to keep tlieir Utters as 

 short as posiible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the apfaranee even ef com- 

 munications containing ititeresting and novel /acts.^ 



Indian Rainfall and Sun-spots 

 I HAVE observed no notice in Nature' of animijortaiit discus- 

 sion which tookjplace a month ago at one of the Royal Society's 

 meetings on Dr. W. \V. Hurler's report on the cycle of rainfall 

 ill India, and its coincidence with the periods of eleven years 

 disclosed by sun-spot observations. As one interested in solar 

 research I have carefully considered that report, and I think 

 the author has made out a case within the limits which he assigns 

 to himself The application of the mathematical law of errors 

 has not altered this opinion in my mind, and from a considera- 

 tion of the whole subject I have been led to the following 

 conclusions : — In the first place I would remark that m certain 



' See abstract of Gen. Slrachey's paper on another page. 



meteorological elements, of which the rainfall throughout the 

 world is probably one, and the barometer in these latitudes is 

 another, oscillations which we regard as non-periodic, are very 

 large compared with periodic variations. The consequence will 

 be that in dealing with a scries of barometric observations 

 in these latitudes, the mean difference of individual obser- 

 vations from the mean of the whole series, or in other words, 

 the mean irregularity, will not be materially modified by the 

 introduction of the comparatively small semi-diurnal variation. 

 But this is no argument against the existence of such a variation, 

 nor is the fact that at Madras the mean rainfall irregularity is not 

 greatly reduced by the introduction of an eleven-yearly cycle 

 any argument against the existence of such a cycle. As a 

 matter of fact, this mean irregularity is reduced, aUJiotigk perhaps 

 not very marliedly, by the introduction of this cycle. The true test 

 of a physical cycle is its repetition, and, since in the present im- 

 portant aspect of this question we cannot, perhaps, calmly wait 

 lor other sixty-four years' observations before venturing a con- 

 clusion, let us now endeavour to break these sixty-fjur years 

 up into periods, and see whether we obtain any traces of physical 

 persistence from this method. Grouping, as Dr. Hunter has 

 done, the sixty-four years' Madras rainfall into series of eleven 

 years, beginning with the first in 1813, we obtain the following 

 table :— 



In this table 3, 4, 5, 6, 7 embrace the maximum rainfall 

 group, and 8, 9, 10, 1 1 the minimum rainfall group, and the 

 sun-spot ma.\imum occurs generally about the beginning of 3, 

 and the sun-spot mimmum a little before II. 



We have, therefore, taking the means of the five maximum 

 rainfall years a result = 53-4 for the whole six series, and also, 

 taking the means of the four minimum rainfall years, a result ot 

 41-6 for the whole si.\ series. 



But we can obtain similar results for each individual series as 

 under : — 



Max. Group. Mia. Group. 



Series A ... 54-7 ... 50-8 



„ B ■■• 51-3 - 347 



„ c ... 54-3 ... 47-5 



„ D - 537 ■■• 396 



„ E ... 42-6 ... 41-2 



„ F ... 63-8 ... 29-3 (incomplete.) 



We have thus considerable evidence of repetition. In con- 

 nection with this it wUl be interesting to see if there is any other 

 physical difference indicated between yf-ars of maximum and 

 uiinimuin spots besides mere difference of rainfall. Now a very 

 interesting additional peculiarity has been indicated by General 

 Slracliey, who has observed that the conception of a cycle of 

 eleven years introduces a decidedly ilimmisticd mean cyclical 

 deviation for ttie minimum period. General Strachey has, no 

 doubt, likewise remarked that this is not cliieHy due 10 those 

 particular years that are nearest the sun-spot niinimiim. I 

 do not, however, see that we have any right in tracing a 

 connection between solar epochs and rainfall values to insist 

 that the mimmum of the one shall correspond absolutely with 

 the minimaai of the other, and the maximum of the one with 

 the maximum of the other. In conclusion, the fact that the 

 introduction of a solar cycle diminishes considerably the devia- 

 tion for minimum years is one of very great interest, since it is 

 these very years that have become so practically important. I 

 trust, therefore, that further attention wUl be devoted to this very 

 interesting inquiry. B.vlfour Stewart 



Natural History Museums 



I AM sure that many readers of Nature will heartily thank 



I'r.jf Boyd Dawkins for his valuable articles just published in 



