April 26, 1894] 



NATURE 



607 



denser, the other consisting of the middle disc and the needle. 

 If a difference of potential exists between these two systems of 

 conductors, then the needle will be deflected, the deflection 

 being approximately proportional to the square of the difference 

 of potential. The sensitiveness of the instrument can be varied 

 by altering the distance between the upper and lower discs and 

 the middle one, or by placing the lower disc in metallic com- 

 munication with the needle and middle disc, instead of having 

 it connected with the upper disc. With a scale at a distance of 

 five metres a deflection of one millimetre corresponds to 014 

 volts. On account of the deflection being proportional to the 

 square of the difference of potential the sensitiveness increases 

 with the deflection, so that when the instrument is employed in 

 measuring a difference of potential of three volts, one milli- 

 metre of the scale corresponds to a change of potential of o'O033 

 volts. 



In No. 7 of the pamphlets which the Physical Laboratory of 

 the University of Leyden is issuing under the direction of Prof. 

 Kamerlingh Onnes, there is an interesting paper by Dr. L. H. 

 Siertsema on the magnetic rotatory dispersion of oxygen. In 

 most substances the magnetic rotatory dispersion approximately, 

 at any rate, follows the law that governs natural rotation, viz. 

 that the rotation varies inversely as the square of the wave- 

 length. In strongly magnetic bodies, such as solutions of iron 

 salts, the dispersion is much greater ; accDrding to Becquerel 

 the rotation being proportional to the fourth power of the wave- 

 length. Oxygen seems to be an exception, for while Becquerel 

 thought he obtained a small dispersion, more recently Ivundt 

 and Rontgen obtained no dispersion. The arrangement of the 

 apparatus employed by the author resembles tRat used byKundt 

 and Rontgen. The gas under high pressure is enclosed with a 

 polariser and analyser in a long tube, and the rotation is obtained 

 by fixing one end of the tube and turning the other, so that 

 torsion is given to the tube. The tube lies in a long magnet- 

 ising coil containing 3600 turns, and through which a current of 

 70 amperes is passed. Some preliminary experiments, made 

 with commercial oxygen at a pressure of about 100 atmospheres, 

 have shown that, contrary to the result given by Becquerel, 

 Verdet's constant for oxygen decreases regularly with increas- 

 ing wave-lengths, and that for violet it is twice as large as 

 for red. 



At a recent meeting of the Kaiserliche Akademie der Wissen- 

 schaften of Vienna, Prof. Klemencic read a paper on the 

 magnetisation of iron and nickel wires by rapid electrical 

 oscillations. From the amount of heat developed in a wire of a 

 magnetic material traversed by electrical oscillations the author 

 calculates, by means of the formula given by Lord Rayleigh 

 and Stefen, the value of ^ (the permeability). The heat 

 developed in the wire under observation was determined by 

 means of a thermoelectric couple, and was compared with the 

 heat developed in a non-magnetic wire under similar circum- 

 stances. The following are some of the values obtained for yu : — 

 Soft iron 118 ; steel wire, soft 106, hard 115; Bessemer steel, 

 soft 77, hard 74 ; nickel 27. These values agree very well with 

 those obtained by Lord Rayleigh and Bauer for very feeble 

 magnetising forces. The results obtained by these observers 

 show that for certain values of the magnetising force the per- 

 meability is constant, and that it afterwards rapidly increases. 

 Now the results obtained by the author show that over the 

 range he is employing /i has a constant value. This fact may 

 be explained either by supposing that the magnetising forces 

 employed are so small that we are dealing with that part of the 

 curve where fi. is constant, or that, although the magnetising 

 forces are much greater than those to which the former 

 supposition limits us, the magnetisation is unable to follow 

 the rapid changes in the magnetising force, so that the magneti- 



NO. 1278, VOL. 49] 



sation never reaches that part of the curve where fx is variable 

 and has very much greater values. A rough estimation has 

 shown that, at least on the surface of the wire and at the com- 

 mencement of the oscillations, the magnetising force exceeds 

 more than a hundredfold the maximum limit within which ^a is 

 constant. Thus in these experiments there must exist a time 

 lag in the magnetisation which must not be confused with the 

 hysteresis. It would also appear that Bauer and Lord Rayleigh's 

 results which refer to longitudinal magnetisation, also apply to 

 circular magnetisation. 



That it is easy to find microbes in the soil capable of as- 

 similating atmospheric nitrogen, if culture media devoid of all 

 combined nitrogen are employed, was pointed out by M. 

 Winogradsky last summer, and in a recent number of the Contptes 

 Rendiis an account is given of important progress made by 

 him in this most interesting subject. By progressive 

 cultivation of a mixture of microbes derived from soil, in a 

 nutritive liquid from which all traces of combined nitrogen were 

 carefully excluded, Winogradsky reduced the varieties present 

 to three bacilli, of which one was finally separated out and dis- 

 covered to be endowed with this function of assimilating 

 atmospheric nitrogen. This organism is strictly anaerobic, and 

 will not grow in either broth or gelatine. It ferments glucose, 

 producing butyric, acetic, and carbonic acid, and hydrogen. 

 The amount of atmospheric nitrogen assimilated is proportional 

 to the quantity of glucose contained in the culture material, and 

 which undergoes decomposition in the presence of this bacillus. 

 Winogradsky concludes his paper by suggesting that this 

 phenomenon of the fixation of atmospheric nitrogen may be due 

 to the union within the living protoplasm of the microbial cell, of 

 atmospheric nitrogen and nascent hydrogen, resulting in the 

 synthesis of ammonia. 



A CATALOGUE of second-hand books, including many rare 

 and scarce volumes on scientific matters, has been issued by 

 Messrs. E. George and Son, Booksellers, Whitechapel Road. 



A REPORT upon the work of the City and Guilds of London 

 Institute daring 1893 has just been issued, and it affords 

 satisfactory evidence of the advance of technical education, both 

 in London and the provinces. A fact well worth recording is 

 that the Salters' Company have recently offered to found, in 

 connection with the Institute, a studentship or fellowship of the 

 annual value of £,\yi, to be awarded for the encouragement of 

 higher research in chemistry in its relation to manufactures. A 

 scheme of regulations for the award and tenure of this student- 

 ship is being drawn up, and the Council of the Institute hope 

 that the action of the Company may result in increased cultiva- 

 tion of original research, and a consequent important advance in 

 the application of chemistry to manufacturing industries. The 

 report shows that the withdrawal of payment on the results of 

 examinations in technology at centres outside the metropolis 

 has had little or no effect in diminishing the number of 

 candidates presenting themselves. It is pointed out that this is 

 partly due to the pecuniary assistance which County Councils 

 are now able to give for the furtherance of technical education, 

 and partly to the recognised value of the certificates granted by 

 the Institute in connection with these examinations. 



We have received a copy of Luke Haward's treatise "On 

 the Modifications of the Clouds" (London, 1803), which has 

 been issued by Dr. G. Hellmann as No. 3 of the reprints of 

 important and rare works relating to meteorology and terres- 

 trial magnetism. The first edition of this work is very scarce. 

 The paper was first presented to the Askesian Society in the 

 winter of 1802-3, and printed in vols. xvi. and xvii. of the 

 Philosophical Magazine. It was the first successful attempt at 

 cloud nomenclature, and up to the present time has formed the 



