48o 



NATURE 



{March 14, 1889 



in Sponges, the majority not yet having seen it. Nothing has as 

 yet been definitely ascertained as to the mode of nutrition of 

 Sponges : from among the several hypotheses, some suppose 

 that the solid organic particles which are suspended in the water 

 are taken up by the ectoderm-cells and digested in the body ; or 

 else that these particles are taken up by the flagellated cells— that 

 is to say, are passed from within outwards ; or that the digestion 

 is cellular, inasmuch as the amoeboid migratory cells take up the 

 food-particles, digest them, and pass on the digestive producls 

 to the rest of the body ; or, finally, that Sponges, like plants, 

 only absorb food-stuffs in solution. The reproduction of Sponges 

 is both asexual and sexual, the first resulting from natural or 

 artificial fission : natural fission, consisting of a simple separa- 

 tion, by constriction, of a portion of the body-substance, occurs 

 in fresh-water Sponges. A further asexual mode of reproduction 

 is by means of buds and gemmules. In the sexual mode of re- 

 production, the females develop eggs all over their surface, and 

 the males spermatozoa, the latter consisting of a head and tail. 

 The egg, after iuipregnation, goes through the various stages of 

 segmentation met with in the higher animals, and then develops 

 into a sac-like embryo. — Dr. Uhthoff" gave an account of his 

 researches on the dependence of visual acuteness in spectral 

 colours upon the intensity and wave-length of the light ; these 

 have been recently reported to the Physical Society by Dr. 

 Koenig (Nature, February 21, p. 408). 



Physical Society, February 8.— Prof. Kundt, President, in 

 the chair. — Dr. Michelson spoke on the normal rate of com- 

 bustion of explosive mixtures of gases. When such a mixture 

 is ignited at one point, and the temperature of combustion is 

 propagated only by conduction from this point, then the surface 

 at which combustion is taking place separates the burnt from the 

 still unburnt portion of the mixture ; the temperature of this 

 unburnt portion is then raised by conduction to that at which it 

 ignites, and it burns. Mallard and Le Chatelier have deter- 

 mined the rate at which this ignition is propagated, by observing 

 the onward movement of the flame i.n a cylindrical vessel filled 

 with the mixture of gases ; Bunsen, on the other hand, allowed 

 the explosive mixture to stream out of a burner with a known 

 velocity, and took this as being equal to the rate of propagation 

 of the combustion in the case where the flame was just on the 

 point of striking back into the tube to which the burner was 

 attached. An objection which may be urged against the first 

 method is that the velocity with which the flame is propagated 

 increases very rapidly the further it travels, so that it is uniform 

 only at the beginning of the explosion. The objection to the 

 second method is, that the flame is continually wavering in and 

 out of the edge of the burner. Dr. Michelson made use, in his 

 experiments, of the dark cone in the centre of the flame, in 

 which the gases are still unburnt, and whose luminous envelope 

 forms the limit of the commencing combustion. When the rate 

 of supply of the combustible gases is uniform, this cone is very 

 steady, and the rate at which the gases stream out from its sur- 

 face is exactly equal to the rate of combustion of these gases. 

 The volumes of the gases consumed were measured in accurate 

 meters, and the size of the luminous envelope to the centre cone 

 of the flame was determined from photographs of the flame. 

 The mixtures examined were those of coal-gas and air, hydrogen 

 and air, carbonic oxide and oxygen, hydrogen and oxygen, car- 

 bonic oxide and air, and of methane and air. With coal-gas 

 and air the rate of combustion increased as the mixture con- 

 tained more of the coal-gas, reaching a maximum with 18 per 

 cent, of this gas, and then gradually became less ; the maximum 

 rate of propagation of the combustion was 70 centimetres per 

 second. With hydrogen and air, the maximum rate was observed 

 \yith 40 per cent, of hydrogen in the mixture, being then 270 cen- 

 timetres per second, and then becoming less. The curve repre- 

 senting the rate of combustion of carbonic oxide and oxygen pre- 

 sented a very different appearance. The maximum rate was only 

 obtained with 75 per cent, of the carbonic oxide, and was about 

 equal to the maximum for coal-gas. For the other three mix- 

 tures, no curves could be drawn. With a mixture of hydrogen 

 and oxygen, the speaker estimated the maximum rate of com- 

 bustion as being about 10 metres per second, but no actual 

 measurement was possible, since the mixture could not be expelled 

 at this rate from the burner, which consisted of a glass tube 

 I metre long. — Prof. Preyer spoke on combination-tones. He 

 endeavoured to prove that difference- and summation-tones have 

 no objective existence. The first of these are the outcome of a 

 co-vibration in the inner ear. When two different tuning-forks 

 are made to vibrate for a long time, and are then damped, and a ; 



third tuning-fork, whose vibration-frequency is only slightly 

 greater than that of the difference in frequency of the other two, 

 is applied to the head, the experimenter hears the corresponding 

 beats. Persons with a defective tympanic membrane in one ear, 

 and a normal membrane in the other, were unable to appreciate 

 difference-tones with the former which they could perfectly well 

 do with the latter. According to the speaker, the summation- 

 tones are really difference-tones, due to the fundamental tone 

 and over-tones of the vibrating forks.— Prof. H. W. Vogel ex- 

 hibited a complete spectrum of cyanogen, which he had obtained 

 by photographing the spectrum of an arc-light produced by a 

 concave grating ; the spectrum extended in the red beyond the 

 line A. Most remarkable was the abundance of lines which 

 were fixed on the photograph, and made visible. The speaker 

 discussed briefly the respective advantages of a concave grating 

 for laboratory experiments on spectra, and of the ordinary prism 

 for practical purposes, especially for observations during solar 

 eclipses. 



BOOKS, PAMPHLETS, and SERIALS RECEIVED. 



Scottish Moors and Indian Jungles : Captain J. T. Newall (Hurst and 

 f C. William Siemens, 3 v " -• • ■ 



E. F. Bamber (Murray).— The Collected Mathematical Papers of Arthur 



Blackett).— The Scientific Works of C. William Sie 



vols. : edited by 



Cayley, vol. i. (Cambridge Press).— A Catalogue of the Newton Manuscripts, 

 Portsmouth Collection (Cambridge Press).— The (Jaraekeeper's Manual : A. 

 Porter (Douglas).— Catalogue of the Fossil Cephalopoda in the British 

 Museum (Natural History), part i : A. H. Foord (London).— Catalogue of 

 the Chelonians, Rhynchocephalians, and Crocodiles, in the British Museum 

 (Natural History), new edition : G. A. Boulenger (London).-A Hand-book 

 of Cryptngamic Botany: A. W. Bennett and G. Murray (Longmans).— 

 Blackie's Modern Cyclopedia, vol. i. : edited by C. Annandale (Blackie).— 

 A Treatise on Chemistry, vol. ii., part 2, new editi n : Sir H. E. Roscoeand 

 C. Schorlemmer (Macmillan) — Henri Sainte Claire Deville ; sa Vie et des 

 Travaux : J. Gay (Paris, Gauthier-Villars).— The House that Jack Built in 

 Diversified Consideration: F. J. Wilson (Reeves) —Encyklopaedie der 

 Naturwissenschaften Erste Abthg., 59 Liefg. ; Zweite Abthg., 51 and 

 52 Liefg. (Breslau, Trewendt).— Our Earth and its Story: edited by P. 

 Brown (Cassell).— Revision of North American Umbellifera: : J. M. Coulter 

 and J. N. Rose. — Notes from the Leyden Museum, vol. x. Nos. 1-4, vol. xi. 

 No. I (Leyden).— Folk-Lore Journal, vol. vii. part i (E. Stock). 



CONTENTS. PAGE 



Through the Heart of Asia 457 



The Testing of Materials of Construction 459 



Our Book Shelf:— 



Packard: " Entomology for Beginners " 459 



Bateman : " The First Ascent of the Kasai : being 



some Records of Service under the Lone Star " . . 460 

 Ramsay : " Tabular List of all the Australian Birds " 460 

 Letters to the Editor: — 



The Meteoric Theory of Nebulae, &c.— Prof. G. H, 



Darwin, F.R.S . 460 



The Formation of Ledges on Hill-sides. {Illustrated.) 



Edmund J. Mills 460 



Weight, Mass, and Force. — Prof. A. G. Greenhill, 



F.R.S 461 



The Inheritance of Acquired Characters. — Prof. 



Marcus M. Hartog 461 



A Fine Meteor.— B. Woodd Smith 462 



Bishop's Ring. — T. W. Backhouse 462 



The Philosophical Transactions. — S 462 



On the Composition of Water. By Lord Rayleigh, 



Sec. R.S 462 



Examinations in Elementary Geometry 464 



Electrostatic Measurement. By Sir William Thom- 

 son, F.R.S 465 



Notes , 466 



Our Astronomical Column : — 



Distribution of Sun-spots in Latitude • 469 



Astronomical Phenomena for the Week i88g 



March 17-23 469 



Geographical Notes . 470 



The Discharge of a Leyden Jar. {Illustrated.) By 



Prof. Oliver J. Lodge, F.R.S 471 



On the Limit of the Solar Spectrum, the Blue of the 

 Sky, and the Fluorescence of Ozone. By Prof. 



W. N. Hartley, F.R.S 474 



University and Educational Intelligence 477 



Scientific Serials 477 



Societies and Academies 478 



Books, Pamphlets, and Serials Received ..... 480 



