May 23, 1895J 



NA TURE 



S5 



order to bring the plane of the slit into exact coincidence with the 

 wire, an image of the slit, produced by a lens with the aid of the 

 electric arc, was thrown upon the wire itself. Since the hammer 

 struck the wire at the point photographed, the motion of the wire 

 was traced from the very first, the commencement of the vibration 

 lieing the most interesting stage. Hard and soft hammers were 

 tried, the latter corresponding to those actually used in the piano. 

 It was found that the duration of contact is longer with feeble 

 than with hard striking. As the force increases, the duration of 

 contact rapidly approaches a limiting value equal to that of a 

 hard hammer of equal weight. But the practically most im- 

 portant resultant was the proof that when a wire is struck at a 

 point between one-seventh and one-ninth of its length, the funda- 

 niental tone has a maximum, and the harmonics — especially the 

 third — are very feeble. Hence a wire thus struck gives its 

 strongest and richest tone. This fact is acted upon by piano- 

 Iniilders, but is not explained liy supposing that the nodes of the 

 higher harmonics are struck, thus preventing their being heard. 

 They are heard, liut are outweighed by the more harmonious 

 ones. 



An interesting paper on the magnetisation of >on in very 

 weak fields, by W. Schmidt, appears in the current number of 

 IVit'dem anil's Annalen. The author uses the magnetometer 

 method slightly modified, a compensating coil being placed on the 

 opposite side of the magnetometer to the magnetising coil. The 

 ■effect of the iron under investigation on the magnetometer 

 needle is compensated by passing a known current through an 

 independent coil of large radius, so that the method is a 

 "zero" one. A Duprez-d'Arsonval galvanometer was used to 

 measure the current, its constant being determined by means 

 of standard Clark cells. The samples of iron and steel under 

 investigation had the form of ellipsoids, the semi-minor axis 

 being 3 m.m. and the semi-major axis 200 m.m. for one set of 

 experiments, and 150 m.m. for the other. The curves obtained 

 for iron and steel show that for fields up to o'o6 C.G.S. units 

 the susceptibility is constant, thus confirming Lord Rayleigh's 

 results. As the magnetising field increases between 0'o6 and 

 0"4 units, the curve giving the relation between the magnetising 

 force and the susceptibility is a straight line. The author 

 sums up the results of his experiments as follows : — Stee] 

 follows weak magnetising forces more quickly than iron. The 

 susceptibility of soft steel is for small magnetising forces 

 greater than that of iron. Thus for fields less than 0'o6 C.G.S. 

 unit the susceptibility of soft steel is to that of iron in the ratio 

 of 4 to 3. For magnetising fields of about I unit the sus- 

 ceptibility of the two is about the same, while for greater 

 field strengths the susceptibility of iron is greater than that of 

 steel. The limits within which the susceptibility remains constant 

 vary considerably for different samples, but the author considers 

 that O'06 C.G.S. unit may be taken as the upper limit with 

 sufficient accuracy for most purposes. 



TllF. May number of the Irish A'(j/;«a//'.f/' well sustains the 

 reputation for utility and general interest which has been ob- 

 tained by this periodical. Mr. R. M. Harrington gives an 

 interesting sketch of the career and writings of the late Mr. A. G. 

 More, a naturalist of unusual versatility, who has contributed 

 greatly to our knowledge of Irish Natural History. Mr. Robert 

 Warren writes on the Breeding Birds of Loughs Conn, Carra, 

 and Mask. Dr. K. Hanitsch gives a brief but valuable account 

 of the Fresh-water .Sponges of Ireland. The distribution of 

 these forms presents certain features of peculiar interest. The 

 eastern part of the island possesses only common European 

 forms, whereas three out of the four species found along the west 

 coast prove to be American. It is pointed out that the forma- 

 tion of gemmulcs gives to the Spongillidce more favourable 

 chances of dispersal than are enjoyed by most other animals. 



NO. 1334, VOL. 52] 



Mr. Clement Reid has examined a sample of marl from which 

 skeletons of the Irish elk had been obtained, and finds that it 

 consists largely of Chara and Potamogeton. He offers an in- 

 genious suggestion to explain the occurrence of skeletons of Cervus 

 megoceros in deposits of CAara-marl. Those familiar with pools 

 containing Chara will be well aware of the appearance of 

 shallowness, and of a solid floor, which is so deceptive. The 

 plants grow to a depth of several feet, but appear to form a carpet 

 of turf just below the surface of the pools; any animal treading 

 on this turf would immediately plunge head-foremost into the 

 water, and in the case of the elk the antlers would almost in- 

 evitably become entangled among the stems of Chara and other 

 still tougher pondweeds. This entanglement theory accounts 

 very well for the fact that the remains of stags are far more 

 abundant than those of hinds. 



A PHOTOGRAPH of the late Prof. J- D. Dana, taken about six 

 weeks before his death, is reproduced in the current number of 

 the American [ournal of Scir-nce, together with a full bio- 

 graphical notice, and a list of his works. 



The "Year-Book of Scientific and Learned Societies" in 

 Great Britain and Ireland, the twelfth annual issue of which has 

 just been published by Messrs. C. Griffin and Co., is undoubtedly 

 a very useful handbook of reference. A general idea of the 

 progress of science during the past year can be obtained from 

 the lists of papers subjoined to the designations of the various 

 societies. 



In the Michigan Mining School theoretical knowledge seems 

 to be well combined with practical training. We notice in the 

 Calendar, just received, that the elements of astronomy is one of 

 the subjects in which all students are examined for entrance into 

 the School. The course of instruction is arranged so that a good 

 foundation is given in the principles of science, and experience 

 and practice are obtained in every subject taught. 



The new editions received during the past week in- 

 clude the first volume of the British Museum " Catalogue 

 of Fishes," containing the Centrarchid.t, Percidje, and Ser- 

 ranida; (part), by Mr. G. A. Boulenger, F.R.S. When the 

 first edition of the work was published, in 1859, the Museum 

 collection of fishes comprised 29,275 specimens. The additions 

 since that date have brought the collection up to twice its 

 dimensions at the time when the original catalogue was compiled. 

 The need for revision will, therefore, be fully understood. In the 

 volume which Iiegins the publication of the new edition of the 

 catalogue, Mr. Boulenger confers a benefit upon ichthyologists by 

 omitting seventy-six imperfectly or incorrectly characterised 

 species. The result of this is that, though many new species 

 are included, the present volume contains only fifty-eight more 

 recognised species than the original one. Mr. Boulenger's list 

 gives 375 species, of which 261 are now represented in the British 

 Museum collection, by 2353 specimens. 



New editions of two technical manuals have reached us 

 from Messrs. Whitt.aker and Co. One of these is " Electricity 

 in our Houses and Workshops," an admirable handbook by .Mr. 

 S. F. Walker, in which the every-day working of common forms 

 of electrical apparatus is simply described. " The Practical 

 Telephone Ilandliook," by Mr. Josejih I'oole, which is now 

 issued in an enlarged form, should prove of increased value to all 

 interested in the methods of telephone working. A new and 

 enlarged edition (the fourth) of Balfour Stewart's " Lessons in 

 Elementary Physics " has been published by .Messrs. Macmillan 

 and Co. In this volume we have a treatise in wliich the whole 

 domain of physics is covered, and which is so arranged that the 

 connections between the various branches of the subject are clearly 

 lirought before the student. Though a quarter of a century old, 



