September 28, 1905] 



NA TURE 



541 



The Department of Agriculture and Technical Instruc- 

 tion for Ireland is publishing a scries of Bulletins upon 

 experimental science, and No. 4 of this series, relating to 

 "Voltaic Electricity," has just been issued. It has been 

 pri'pared by Mr. James Comerton, and is a useful little 

 pamphlet of thirty pages with numerous illustrations. The 

 author states in the introduction that the experiments de- 

 scribed are merely intended to introduce the student to 

 the more systematic study of electrical measurements. 

 When the student has worked through the forty-three 

 experiments described in this pamphlet, it is hoped that 

 he will have a fair general working knowledge of voltaic 

 cli'ctricity — its generation, measurements, and the purposes 

 to which it can be applied. Primary cells, resistances, 

 galvanometers, and voltameters are illustrated, and their 

 use is described in these pages. The handbook should 

 prove a useful addition to the literature of elementary 

 electrical measurements. 



The principal centres of the calcium carbide industry in 

 France are in the Alps and Pyrenees. At present, accord- 

 ing to a writer in the Journal of the Society of Arts, there 

 are eleven manufactories capable of producing 40,000 tons 

 of calcium carbide annually. The total output sold during 

 1004 may be estimated at 18,000 tons. The average yield 

 of gas per unit of weight of carbide is about 40 gallons 

 per pound. The cost price per ton of calcium carbide in 

 Europe was estimated by Prof. Lefevre, of the Ecole des 

 Sciences, Nantes, in 1897, at from 8/. to 10/. M. . Pictet, 

 however, in the same year, thought that the product might 

 be made at the cost of a little more than 3/., by the use 

 of a new furnace. Theoretically, said Prof. Lefevre, one 

 pound of calcium carbide ought to produce, by its action 

 upon water, about seven ounces of acetylene. It has been 

 stated by one of the most important of the French firms, 

 speaking of the production of 1904, that this was disposed 

 of at SI. per ton, the standard accepted and declared being 

 about 40 gallons of gas per pound. The product at the 

 factory realises 8/.. per ton, and the rate for the retail 

 dealer is 14/. These figures demonstrate the advances 

 made in manufacturing since the publication cf Prof. 

 Lefevre's treatise in 1S97. 



Prof. d'Arsonval describes in the Bulletin of the French 

 Physical Society a new and simple form of apparatus 

 manufactured by the Soci^t^ Frangaise de I'Ac^tyl^ne 

 dissous, which serves for the generation and automatic 

 compression of oxygen. The gas is generated by the com- 

 bustion within the compression cylinder of a combustible 

 substance mixed with potassium chlorate, the heat pro- 

 duced being sufficient to liberate the whole of the oxygen 

 from the chlorate. The largest form of apparatus, the 

 industrial type, gives a production of about Co cubic feet 

 of oxygen per hour. A new form of oxyacetylene burner 

 is also described by means of which a very intense light 

 is produced by allowing the jet to impinge upon a suitable 

 mixture of the rare earths ; lime and magnesia are useless 

 for the purpose, as they are rapidly fused and channelled 

 by the intense heat of the oxyacetylene flame. 



During the past few years doubts have been expressed 

 by several investigators, notably by Fitzgerald, Kahlen- 

 berg, Quincke, and Traube, of the correctness of Van 't 

 Hoff's hypothesis that the osmotic pressure of solutions 

 is purely a kinetic phenomenon due to the impact of the 

 molecules of the solute against a membrane impermeable 

 to them. This hypothesis has been so fertile of results 

 and is so intimately associated with the progress of modern 

 chemistry that any arguments of a subversive tendency 

 NO. 1874, VOL. 72] 



have, generally speaking, received little attention. In a 

 recent number of the Atti del Lincei (vol. xiv., ii., p. 5) 

 Prof. A. Battelli and A. Stefanini have brought forward, 

 however, a number of facts which, if subsequently verified, 

 are likely to prove insuperable objections to its validity. 

 A necessary consequence of Van 't Hoff's hypothesis is 

 that isosmotic solutions should, under similar 'conditions, 

 be equimolecular ; but it is stated that several cases have 

 been observed in which solutions possessing very different 

 molecular concentrations are in osmotic equilibrium. The 

 characteristic of these solutions is that they have equal 

 surface tensions, and it is contended that osmotic pressure 

 is essentially a capillary phenomenon. Osmosis would 

 then be a tendency to equalise the surface tensions of the 

 liquids on the two sides of the membrane. The further 

 developments of the authors' experiments will be watched 

 with interest. 



.An interesting lecture device for illustrating the super- 

 position of simple harmonic motions of different periods 

 has been submitted to us by Mr. W. C. Baker, of the 

 School of Mining, Queen's University, Kingston, Ontario. 

 \ horizontal bar (about 4 cm. deep and 15 cm. long) carries 

 a pointer about 50 cm. long rigidly attached to it. This 

 system, which must be as light as possible, is suspended 

 by two hinges which permit it to oscillate freely about 

 a horizontal axis. To the underside of the bar are 

 attached two pendulums (100 cm. and 75 cm. long) the 

 bobs of which are of equal mass, say 250 grams each. 

 If the pendulums be displaced together through an arc 

 of, say, 15° and then released, the pointer will be set 

 vibrating through an arc which will vary from a maxi- 

 mum when the pendulums are in phase with one another 

 to very approximately zero when they are in opposition, 

 thus illustrating the formation of beats. There is, of 

 course, no obvious relation between the amplitude of the 

 motion of the pointer and that of the pendulums ; the 

 oscillations of the latter give rise to periodic forces upon 

 the horizontal bar, and the pointer indicates the resulting 

 motion. We may point out that a somewhat analogous 

 device was shown by Lord Rayleigh during a recent course 

 of lectures at the Royal Institution. 



Lc Radium for August contains various articles and 

 reviews on all the branches of radio-activity, together with 

 a summary of current researches in this subject. 



The Revue Scieiitifiquc (September q) contains an 

 interesting summary on trypanosomes and trypanosomiasis 

 by Dr. Brumpt. In addition to the ordinary pathogenic 

 forms, the trypanosomes of birds, reptiles, and fishes 

 receive notice. 



According to La Natur: (September 16), the ravages of 

 the phylloxera in northern Spain are very serious, many 

 of the older vineyards being almost destroyed ; and it is 

 becoming a question whether it will not be necessary to 

 substitute cereals and fruit for the vine in the affected 

 districts. 



The Bulletin of the Johns Hopkins Hospital for 

 September (xvi.. No. 174) contains an interesting historical 

 article on Cotton Mather's rules of health by Prof. William 

 Thayer, together with papers of medical interest. Cotton 

 Mather was a divine who was born in Boston in 1663, a 

 learned man with a remari^able literary style, and his 

 rules are often very quaint. 



In the August number of the Journal of the Royal 

 Microscopical Society, Mr. Conrady writes on the appli- 

 cation of the undulatory theory to optical problems, and 



