Jan. 27, 18S7] 



NATURE 



295 



Hand-book of Zoology, with Examples from Canadian 

 Species, Recent and Fossil. By Sir J. William Dawson, 

 LL.D., F.R.S., &c. Third Edition, revised and enlarged. 

 (Montreal : Dawson Brothers, 1SS6.) 

 In this little work, the President of the British Associa- 

 tion for the Advancement of Science has concentrated 

 into some 300 pages a very fair account of the principal 

 divisions of the animal kingdom. It is specially adapted for 

 Canadian students, inasmuch as the examples of every 

 group are selected, as far as possible, from species found 

 within the limits of the Dominion. The fact of the 

 volume having reached a third edition shows that Sir 

 William Dawson's plan and method have been appre- 

 ciated. That the arrangement adopted is altogether un- 

 exceptionable, and that all the most recent discoveries in 

 zoological science are taken advantage of, we could not 

 fairly say. For example, Eozoon is still treated of as if 

 it were without doubt an organic structure ; the unques- 

 tionable affinity of the larval Ascidian to the Vertebrate 

 embryo is but faintly alluded to ; and the much-t'ilked- 

 about Pcripatus — one of the most singular types of 

 Arthropodal life — seems to have been altogether omitted 

 from the list. Yet there is, in the main, an absence of 

 the serious errors which are too often found in such 

 manuals. The volume is well illustrated and well printed, 

 and will, we have no doubt, be of much service as a 

 text-book in Canadian schools of science. 



Theory of Magnetic Measurements. By Francis E. 



Nipher, A.M., Professor of Physics in Washington 



University, President of the St. Louis Academy of 



Science. (New York : D. Van Nostrand ; London : 



Trijbner and Co., 18S6.) 

 During the last twenty years there has been consider- 

 able activity amongst observers on land and at sea in 

 adding to our knowledge of the magnetism of the earth, 

 and it is certainly desirable, if not necessary, that those 

 busy workers, who are only acquainted with the practical 

 use of the instruments employed, should know something 

 of the theory of the magnetic measurements upon which 

 they may be engaged. 



To those conducting magnetic surveys under English 

 auspices, the article on Terrestrial Magnetism in the 

 "Admiralty Manual of Scientific Inquiry " has proved a 

 valuable aid in showing both what was required and 

 the practical means of obtaining observations on land 

 and sea, with the methods of calculating the results. 

 The theory of the subject, however, is beyond the intended 

 scope of the Manual. 



The magnetic survey of the United States has, during 

 the period under consideration, been continuously carried 

 on under the Government and private enterprise, and 

 Prof. Nipher has been one of the diligent workers, as 

 shown by his survey of Missouri, published in NATURE, 

 (vol. xxiii. p. 583). In the book before us he com- 

 bines some excellent practical information for those 

 undertaking the observation of the three magnetic 

 elements on land, with the theory of the several magnetic 

 measurements thus made. 



A large portion of the book is necessarily occupied by 

 the theory of the horizontal force magnetometer and its 

 several parts. Here the reader will find some differences 

 from the English notation. For instance, H is substituted 

 for X when denoting the horizontal force, and I for K, as 

 the moment of inertia of the deflecting magnet. A more 

 important departure from the usual method of calculation 

 will be noticed in the omission of the coefficient of induc- 

 tion /i, which has been so entirely rejected as not even to 

 be discussed. The retention of this coefficient has already 

 been challenged elsewhere, but the general support of 

 European practice seems to forbid any change until its 

 place in our formulae has been proved unnecessary. In 

 the concluding pages there is an article on the systems of 



units adopted in magnetic measurements, and plates of 

 the unifilar magnetometer and dip-circle generally used. 



The appendix is devoted to a discussion of the method 

 of least squares in the reduction of observations, an 

 article on graphic methods, with the aid of which so much 

 may be done to shorten the labour of computation, and 

 some tables giving the times of the elongation of Polaris 

 with its corresponding azimuth for the years 1886-95, from 

 which the true meridian may be readily deduced for 

 declination-observations. These tables will probably be 

 found convenient in latitudes between the northern tropic 

 and the .-\rctic circle. 



The large domain of magnetic observations at sea is 

 not touched upon, but intending observers on land should 

 be pleased to possess a book of this kind, which might be 

 included in their travelling equipment without fear of 

 adding much to the weights to be carried. 



The Coming Deluge of Russian Petroleum. By C. 



Marvin. (London : R. Anderson and Co.) 

 This pamphlet does not pretend to add to our limited 

 knowledge of the origin of petroleum or of its connection 

 with the Tertiary deposits and volcanic activity of the 

 Caucasus. It is in reality an appeal to English enter- 

 prise to direct its attention to at least the carrying trade 

 of a district so rapidly growing in industrial importance. 

 The enormous figures given [e.g. more than a million 

 gallons a day from a single well) are enough, however, to 

 stimulate scientific as well as Stock- Exchange inquiries, 

 and the development of communications between Baku 

 and the West is sure to be, sooner or later, fruitful in geo- 

 logical results, G. C. 



LETTERS TO THE EDITOR 



[The Editor Joes not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertaki to 

 return, or to correspond itiith the writers of, rejected manu- 

 scripts. 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 insure the appearance even 

 of communications containing interesting and novel facts. ] 



The Cambridge Cholera Fungus 



I n.WE read with great surprise Mr. G.irdiner's letter in your 

 issue of January 20 (p. 271). We are there told that on recon- 

 sideration Mr. Gardiner has now come to the conclusion that 

 the organism which he saw in Prof. Roy's preparations of the 

 inte-tinal mucous membrane — which Prof Roy took to be the 

 more usual and typical form, and which Mr. Gardiner then 

 thought to belong to the Chitridiacese — is probably the particular 

 phase in the life-history of Bacterium known as an involution 

 form, i.e. " a thin and somewhat moniliform fdament which at 

 one end exhibited a distinct nodular swelling." If Mr. Gardi- 

 ner has studied the filaments of a growth of mould in animal 

 tissues, he must have come across numbers of such forms. But 

 granting for the sake of argument that what Mr. Gardiner saw 

 in Prof Roy's specimens bears a resemblance to and is in reality 

 an involution form of Bacterium, how about the branched threads 

 figured in the Report by Messrs. Roy, Brown, and .Sherrington 

 in No. 247 of the Proceedings of the Royal Society, on p. 179 ? 



Each of these two figures introduced here, no doubt as typical 

 representations of the organisms in the mucous membrane, sho s 

 unmistakably br.anched mycelial threads of a true fungus. If 

 what Mr. Gardiner has seen in Prof. Roy's preparations is an 

 involution form of some Bacterium, then the branched threads 

 figured in Messrs. Roy, Brown, and Sherrington's Report are 

 something else, unless somebody started the novel and extra- 

 ordinary view that a Bacterium possesses branched mycelial 

 threads like a true fungus. 



I should be glad to hear Mr. Gardiner's opinion as to these 

 branched mycelial threads figured on p. 179 of the Proceedings 

 of the Royal Society, No. 247, in the Report by Messrs. Roy, 

 Brown, and Sherrington. E. Klein 



