March 29, 1894] 



NA TURE 



503 



ascribed to them as food for the deep-sea forms ; though 

 not weighted, like the radiolatians, diatoms, «S:c., with 

 silex, still they might in time fall from the table of the 

 upper waters on, or rather down, to that of the hungry 

 deep-dwellmg forms. In the chapter on the relations of 

 the Abysmal zone and the origin of its fauna, the author 

 introduces the new classification of the ocean fauna, 

 " Plankton," " Nekton," and " Benthos," and he is good 

 enough to write that though "it will not be necessary to 

 use these terms very frequently in this little book, it may 

 be advisable for the reader to bear in mind that in any 

 exhaustive treatise on the marine fauna such terms would 

 be used and employed.'' We, however, only find in the 

 index one reference to them, and that the one we have 

 just quoted ; nor in the following chapter, treating of the 

 characters of the deep sea fauna, does the author employ 

 them, though here their use might have assisted the 

 meaning. Perhaps this Greek armour was found too 

 cumbrous. 



The last paragraph of this chapter we would have pre- 

 ferred omitted. We cannot see the relevancy of Moseley 

 in comparing the deep sea fauna, even " as a whole, ' as 

 in any way similar to the flora of the high mountains. 

 If some of the deep-sea forms are dwarfed, this is surely 

 the exception, and giants of almost all the groups are to 

 be found among them ; whereas what gigantic represen- 

 tatives of any group are to be found on the mountam tops ? 



The remaining four chapters treat of the Protozoa, 

 Coelentera, Echinoderma, Vermes, MoUusca, Arthropoda, 

 and Fish of the deep sea. They open with a regret that 

 '"although thousands of species of animals have been 

 described in the volumes that have been devoted to deep- 

 sea work, yet the number of the sub-kingdoms and classes 

 remains the same," and conclude with a hope, in which 

 we join, "that in the future there may be a new stimulus 

 given to deep-sea research, and that the many un- 

 solved problems may be again seriously studied and 

 eventually solved." 



A Treatise on Ele^nentary Hydrostatics. By John 



Greaves, M.A. (Cambridge University Press, 1894.) 

 A BRIEF examination of this treatise is sufficient to 

 allow us to form a favourable opinion of its contents. 

 Nearly every proposition or description shows that the 

 author is a thorough master of his subject, and, what is 

 also of equal importance, can impart his knowledge to 

 his readers in language both concise and fresh. The 

 treatise is intended for those preparing for the first part 

 of the Mathematical Tripos, and is different from other 

 elementary works on the same subject in the following 

 manner : In this Tripos examination one is now allowed 

 to use the notation of the calculus, which for some 

 students is a great boon, in that problems can be more 

 easily solved, and in less time. We are thus presented 

 in the text of this treatise not only with the usual proofs, 

 but with alternative proofs when the use of the calculus 

 is a distinct advantage. This alteration will be found an 

 improvement. The definition of a fluid, from which 

 are deduced the principles of the subject, is given 

 as " a substance which will yield to any continued 

 shearing stress, however small, or," in other words, 

 "when a fluid is in equilibrium, the stress across any 

 plane in it is entirely normal to that plane." 



Among other useful additions to the subject may be 

 mentioned propositions relating to a heterogeneous fluid 

 in equilibrium under any system of forces, and some 

 cases of simple motion, the latter of which may be left 

 for a second reading. In chapter ix. the author deduces 

 several well-known capillary phenomena from the ex- 

 perimental result that the energy of a material system 

 depends to a great extent on the surfaces separating the 

 different subs:ances. 



As the book is printed in clear type and contains 

 neat diagrams, it will be sure to find favour with students. 



NO. I 274, VOL. 49] 



LETTERS TO THE EDITOR. 



The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

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

 matiuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications. ] 



Sun-spots and Magnetic Disturbances. 



The note in Nature for February 22, 1894 (p. 397) ccn- 

 cerning "Sun-spots and Magnetic Disturbances" illustrates 

 most clearly the necessity for the adoption of a proper method 

 in order to arrive at any conclusion respecting the relation 

 between these phenomena. I must continue to insist, as I have 

 done heretofore in the columns of Nature and elsewhere, that 

 the study of the periodicity of magnetic storms and auroras at 

 intervals of about twenty-seven and one quarter days must 

 precede that of the attendant solar conditions, otherwise no 

 results will be obtained. For example, during the month of 

 August 1893, to which the note above mentioned refers, sun- 

 spots were so numerous that it would be utterly impossible to 

 determine which group, if any, were in a location upon the sun 

 capable of originating terrestrial magnetic effects. The proper 

 way is to begin by disregarding solar conditions entirely, and 

 arrange the magnetic storms or auroras of the period that it 

 is de>ired to study, in series as they actually occurred at the 

 twenty-seven and one quarter day interval. This being done, it 

 is possible at a glance to determine what particular solar con- 

 ditions reappear invariably when magnetic perturbations are 

 recorded. In this way, and. in this way alone, it becomes 

 evident that whenever these magnetic effects appear, there is 

 always a disturbed portion of the sun at the eastern limb and 

 near the plane of the earth's orbit in that location. If the series 

 of recurrences is sufficiently persistent to last through many 

 solar rotations, it will be lound that the disturbed area con- 

 tinues to have its effect in spite of considerable variations in the 

 size of the spots, and that at times these effects may continue 

 even when nothing but groups of faculgs remain, these being 

 however, unusually bright and extensive in such a case. By 

 following the history of such recurrences into the portion 

 of the year in which any given disturbed portion of 

 the sun is at a distance from the plane of the earth's orbit, when 

 at the eastern limb, it is found that outbreaks of violent thunder- 

 storms, which do not produce any disturbance of the magnetic 

 needle, take the place of magnetic storms and auroras in the 

 regular order of recurrence. There have been some phenome- 

 nal illustrations of this the past winter. Usually in this part 

 of the United States a thunderstorm in winter is very rare, and, 

 if it occurs, stands forth as a prominent event. Thus the 

 thunderstorms of Christmas-day and night, in which buildings 

 were struck by lightning in this State, were most exceptional, 

 and, falling as they did upon the proper date to form the con- 

 tinuation of the strongest and most persistent series of thunder- 

 storms and auroras that has been current the past year, were 

 most striking. The above method of attacking the question is 

 that which the writer has gradually developed for the purpose 

 of systematic study. The relation having once been established 

 by tracing the history faithfully and in detail, in the manner 

 described, it is no longer absolutely essential to enter into the 

 question of periodicity in order to secure evidence bearing upon 

 the question. As soon as it is known what has to 1 e looked for, 

 it will only lie necessary, when any very large increase of thunder- 

 storms occurs, or any notable magnetic perturbations, as the case 

 may be, to look at the proper part of the sun, and see whether 

 it is the seat of disturbance. In this way it will be found that it is 

 not the size of solar disturbances, but their activity at ihe 

 critical date when they are in the proper location, that deter- 

 mines the terrestrial effects to which reference has been made. 

 Thus it is a question throughout of the adoption of a proper 

 method of investit;ation. M. A. Veeder. 



Lyons, N.Y., March 12. 



Dredging Expedition at Port Erin. 



The Liverpool Marine Biology Committee organised a 

 dredging expedition from the Port Erin Biological Station at 

 Easter. The parly of a dozen naturalists included several 

 members of the committee, Mr. I. C. Thompson, Mr. A. 

 Leicester and Prof Herdman, Prof. Weiss, Dr. Hurst, Mr. 



