546 



NATURE 



[September 14, 191 1 



OUR BOOK SHELF. 



Leitjaden jiir das mikroskopisch-zoologische Prakti- 

 kum. By Prof. W. Stempell. Pp. 1V + S4. (Jena: 

 Gustav Fischer, 1911.) Price 2.80 marks. 

 The medical practice of teaching histology in a 

 separate section of the course is, we regret to see 

 from the author's preface, becoming adopted in bio- 

 logical teaching; and to this circumstance Prof. 

 Stempell refers for the origin of his book, since he 

 has adapted its contents to meet the requirements of 

 beginners who wish to traverse rapidly a course in 

 comparative microscopy apart from the dissections, 

 museum work, and naked-eye observations with which 

 microscopic work has been hitherto so usefully 

 associated. 



At first all is smooth sailing. A lucid introduction 

 on apparatus paves the way to five lessons on 

 protozoa. The methods of obtaining, examining, and 

 preparing the material are admirably explained. The 

 paragraphs are numbered, so that references to proce- 

 dure can be made at once, and the most instructive 

 and accessible members are dealt with before those 

 which present greater difficulties. A few pages 

 later, however, we find Anthozoa, Ctenophora, Tur- 

 bellaria, and Trematodes dealt with in a single section, 

 which we must suppose represents three to four hours' 

 work. On the other hand, far more attention is given 

 to the Nematoda than is usual in an elementary 

 course. The section devoted to vertebrate histology is 

 very incomplete. 



The illustrations have a special value, since they 

 are in every case photographic reproductions of actual 

 preparations, but as no attempt is made to explain 

 what they show such figures cannot be said to be 

 useful to the student. The chief use of the book lies 

 in the methods which it suggests for the collection 

 and preservation of material. In this respect it will 

 be of considerable service, but as an attempt to present 

 a working course in comparative histology, we should 

 be sorry to see Prof. Stempell 's recommendations 

 carried out without considerable modification. 



F. W. G. 



Early Essays on Social Philosophy. Translated from 



the French of Auguste Comte bv H. D. Hutton. A 



new edition with additional notes, and with an 



introduction bv Frederic Harrison. Pp 3S2 



(London : George Routledge and Sons, Ltd. ; New 



\ork: E. P. Dutton and Co., n.d.) Price is. net. 



These six essays, written by Comte between the ages 



of nineteen and twenty-one, appeared in vol. iv. of 



the _ Positive Polity," published in 1877. Their 



special interest is that they prove the unity of their 



author _s life- work— the coherency and consistency of 



his scientific philosophy and his social polity— as 



fga'nst (he view of Littre, that the two are disparate, 



the later work a backsliding from the principles of the 



earlier. 



The third essay is the longest and the most im- 

 portant. It contains in exact and decisive form the 

 famous Law of the Three States, which "all subse- 

 quent thinkers have regarded as Comte 's triumphant 

 discovery," and is the basis and the justification of 

 Positivism. I-rom the nature of man's intellect each 

 branch of knowledge in its development is necessarily 

 obliged to pass through three stages— the theological, 

 the metaphysical, and the scientific or positive. 



The fourth and fifth essays give a risumi of the 

 entire system of the "Positive Politv " as meaning a 

 social and religious reorganisation "of society based 

 upon a scientific study of human nature. 



Mr. Frederic Harrison supplies an excellent little 

 introduction to this new edition. 



NO. 2185, v OL. 87] 



Technique de Psychologie Expe'rimentelle de Toulouse, 

 Vasckide et Pieron. By Ed. Toulouse and H. Pieron. 

 Second edition, tome i., pp. xii + 303; tome ii., 

 pp. xvi + 288. (Paris: Octave Dion et Fils, 1911.) 

 Price 10 francs the two volumes. 

 This edition, now expanded to double the former size 

 and comprised in two volumes, is virtually a new 

 book. Far more space is devoted to the description 

 of apparatus than formerly. Pieces of apparatus are 

 illustrated, many of which are quite unknown in the 

 psychological laboratories of this country. Not only 

 for this reason, however, is the work likely to be of 

 little value to elementary students of the subject on 

 this side of the Channel. The authors err in laving 

 no stress whatever on an acquaintance with the 

 psycho-physical methods, and on the importance of 

 obtaining introspective data in psychological experi- 

 ment. It appears to be their object merely to 

 "describe apparatus," much as the authors of a book 

 on experimental physics would do, leaving on one 

 side methods of procedure as if they could be picked 

 up haphazard in the laboratory, and neglecting the 

 introspective data obtainable from the subject of the 

 experiment as if they did not exist ! For the instructor 

 or the advanced student, however, the work is of 

 considerable interest. The apparatus, unfamiliar in 

 this country, is excellently described ; and there are 

 several novel experiments which appear to have 

 premising value. 



LETTERS TO THE EDITOR. 



[The Editor doss not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

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

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communication*.] 



Rainless Thunderstorms. 



From the letter signed " E. G. " in your issue of 

 August 31, it would appear that the Meteorological Office 

 has not abandoned the ion condensation theory of the 

 origin of atmospheric electricity. Now, there are many 

 difficulties in accepting that theory. For instance, before 

 condensation can take pU.ce on ions, there must first be 

 dustless air ; otherwise the necessary supersaturation cannot 

 take place ; and one naturally asks, Has anyone ever found 

 dustless air in our atmosphere? So far as records go of 

 air up to 10,000 feet, this has not yet been found, and it 

 does not seem likely that it ever will be found, as the hot 

 air carrying up the aqueous vapour to form clouds always 

 carries up with it plenty of dust to act, if one may use 

 the simile, as the return ticket to bring the water back 

 to the surface of the earth. As much of this dust is very 

 fine, only falling a few centimetres in a day at low level, 

 it is likely to go wherever the moist air goes — in even the 

 more rarefied regions of the upper clouds. Further, there 

 is the constant supply of fine dust from the upper regions 

 due to the disintegration of meteors, so that the air at 

 cloud levels is likely always to have plenty of dust and 

 condensation on ions seems impossible. 



Another difficulty of importance is, Has anyone ever 

 shown that it is possible for a cloud to form on ions under 

 the conditions in which condensation takes place in the 

 atmosphere? It is true that clouds can be formed on ions 

 under experimental conditions ; but in these the expansion 

 must lie made with explosive quickness, because if the 

 on is in. m1.' slowly only a few ions become centres 

 of condensation, and these rapidly grow to the size of rain- 

 drops in the highly supersaturated air ; and these drops in 

 falling relieve the supersaturation of the air some distance 

 round them all along their path, so preventing other ions 

 becoming centres of condensation, and only rain, not cloud, 

 is produced. It would appear that these and other difficul- 

 ties are worth considering hefore accepting the ion con- 

 densation theory of the electrification of clouds. 



