162 



NATURE 



\jnne 14, i 



Society. The dielectric they used was carbon bisulphide 

 (CS 2 ), and the' beam of light passed through about four inches 

 of the liquid. The presence and intensity of the electric 

 field was evident to all by the brightness of the screen. 

 They showed experiments to illustrate the fact that the repulsion 

 of similarly electrified bodies may be regarded as an attraction 

 between each of them and surrounding objects. They have devised 

 an experiment visible to a large audience to show that in an electric 

 field the structure of the CS 2 becomes crystalline — that is, the 

 optical properties along and transverse to the electric lines of 

 force are different ; in other words, the velocities of propagation 

 of light vibrations differ when parallel and perpendicular to the 

 lines of force, contrary to the view formerly held on the Continent 

 that the effect is due to unequal expansion. They were able to 

 increase the stress so that the liquid displayed colours even to 

 the green of the second order ; and by observing the spectrum of 

 the light passing through the field, black bands enter at the 

 violet end and traverse its whole length as the potential rises. 

 Faraday's experiments and speculations, Maxwell's mathematics 

 and theories, are rapidly becoming acknowledged facts ; and the 

 apparatus of Messrs. Riicker and Boys will materially assist in 

 spreading a knowledge of the confirmation which those theories 

 receive from the work of Kerr and Quincke. 



Blondlot {Comptes rendus, January 30, 1888) has been 

 working in the same direction, but with vibratory discharges 

 from a Leyden jar, in order to test the existence or non-exist- 

 ence of retardation in the optical effects. He could see no 

 retardation. 



Cowles's process for the production of aluminium from its 

 ores by the direct action of an electric current of 5000 amperes 

 in an electric furnace has now become an industry. Works have 

 been started near Stoke, and bronzes of wonderful quality are 

 supplied at comparatively cheap prices. 



There is a fashion in experimental investigation as in every- 

 thing else. Self-induction is played out, and now the counter 

 E.M. F. of the arc is passing through the same phase. Uppen- 

 born {Beib/dtter, No. 1, 1882, p. 83) is the last inquirer. He 

 finds for a current of 77 amperes and 10 mm. carbons, that 

 a = 35 -4 to 45-4 ; b = 1 74 to 3-2 in Edlund's formula — 



E = a + b/. 

 Since a decreases both for an increase of current and for an 

 increase in the section of arc, he leans to a resistance hypothesis 

 rather than an E.M.F. 



Klemencie {Beib/dtter, No. I, 1888, p. 57) finds the specific 

 inductive capacity of mica to be 6 64 ; Cohn and Arons {Ann. 

 der Physik, No. 1, 1888, p. 13) that of distilled water 76, 

 ethyl alcohol 26"5, amyl alcohol 15, and petroleum 2'04. 



Palmieri (March 1888) has observed that in a bright clear 

 sky, with a high and steady barometer, and every indication of 

 continued fine weather, the electrometer will give an indication 

 of change long before the barometer. 



W. Kohlrausch {Electrolechnische Zeitschrift, March 1888) 

 has estimated the current and quantity of electricity in a 

 lightning-flash. He calculates that it will take 9200 amperes 

 to melt a copper rod of 2 '5 centimetres diameter. Preece's 

 constant (Proc. R. S., March 18S8) makes it 10244. Such a 

 current concentrated in a flash would contain fr mi 52 to 270 

 coulombs, which would decompose from 5 to 25 milligrammes 

 of water, and from 9 to 47 cubic centimetres of explosive gas. 

 If this energy were stored up and distributed for electric lighting, 

 it would require from 7 to 35 such flashes to keep one glow 

 lamp alight for an hour. 



Vogel {Electrotechnische Zeitschrift, January 1888) had pre- 

 viously calculated the relative value of copper and iron as 

 lightning- protectors, giving iron a section 25 times that of 

 copper to act with equal efficiency. Preece's constants give the 

 relative efficiency — 



Iron 3148 



Copper 10244 



for equal diameters — that is, an inch rod will fuse with the above 

 currents in amperes ; or, if we take the same current, say 300 

 amperes — 



Iron ... ... ... ... o - 2o86 



Copper 0095 



are the diameters in inches of the wires such currents will fuse, 

 or in the ratio 2 '2 to 1 ; Vogel's ratio being 13 -54 to 9-6. 



Vogel did not consider the emissivity of the surface, and there- 

 fore his results are not so accurate as Preece's experimental 

 figures. 



That patient worker, II. Tomlinson, has proved that the 

 temperature at which nickel begins to lose its magnetic 

 properties is between 300 and 320° C. ; but that the rate of 

 decrease of magnetic permeability, and the temperature at which 

 permeability practically vanishes, vary with the magnetizing 

 force, and hence the widely different results by different 

 observers. Faraday made the former point 330 to 340° ; 

 Becquerel 400° ; Pouillet 350° ; Chrystal 400 . Iron behaves 

 in the same way : permeability vanishes between 750° and 770° 

 according to Ledeboer. 



Prof. Ewing and Mr. Cowan have been examining the 

 magnetic qualities of nickel on the same lines as the former 

 examined iron. They confirm Sir W. Thomson's observation 

 that longitudinal pull diminishes magnetism to a surprising 

 extent. Their paper in the Philosophical Transactions will be 

 looked forward to with much interest. 



S. Arrhenius {Wiener Berichte, xcvi. p. 831) has shown 

 that the electrical conductivity of chloride and bromide of silver 

 was influenced by the intensity of the rays of light which fell upon 

 the salts. It was most intense at G of the spectrum, and is 

 therefore an effect of light, and not of heat. 



F. Kohlrausch {Wiedemann's Annalen, No. 4, 1888) has 

 shown that the electric conductivity of 



Hard steel is 3*3 

 Soft steel ,, 5 '5 



Wrought iron ,,76 



mercury being I ; while their thermal conductivities in C.G.S. 



units were — 



Hard steel C062 



Soft steel o'lii 



Wrought iron 0*152 



the ratios being the same. Hence the conditions that determine 

 the conduction of heat and electricity are the same. 



Mr. C. V. Boys's interesting magnetic and electric experi- 

 ments with soap-bubbles, and his wonderful manipulative skill, 

 remind old habitues of the Royal Institution how exquisitely 

 Faraday handled sjap-bubbles blown with oxygen to illustrate 

 the magnetic character of that gas. Mr. Boys blows one bubble 

 inside another, and, on bringing the two into an electric field, 

 the perfect indifference of the inner one to any change of 

 potential clearly shows that electrification is confined to the 

 absolute surfaces of a conductor, and that it is not felt at any 

 depth within it, however small. 



WHEA T CULTIVA TION} 



'"THE most interesting sections of this number of the Journal 

 -*- are those bearing upon the subject of wheat cultivation. 

 The permanent wheat and barley experiments at Woburn, 

 reported upon by Sir John Lawes, Bart., is followed by a paper 

 upon the condition of wheat-growing in India by Dr. George 

 Watt, Reporter upon Economic Products to the Government of 

 India. Next comes an article by Mr. W. E. Bear upon the 

 Indian wheat trade. Lastly, in this connection, comes a highly 

 interesting account of modern improvements in corn-milling 

 machinery. These four papers occupy one-third part of the 

 volume, and taken in connection with each other throw consider- 

 able light upon the difficulties under which the English wheat- 

 grower is struggling. Dr. Watt and Mr. Bear both show the 

 extraordinary extent of the wheat-producing area of our Indian 

 Empire, and the rapidity with which this vast field is being 

 opened up. With reference to the latter point men in middle 

 life are scarcely likely to realize the fact that in 1853 there were 

 in all only zo\ miles of railway in India, that in 1873 there were 

 5695 miles of railway, while in 1887 there were 13,386 miles. 

 Telegraphic communication with India was first opened in 1865, 

 and the opening of the Suez Canal in 1869 was scarcely of less 

 importance in developing her trade— first, by shortening the 

 passage, and secondly, by mitigating the risk from wheat weevil. 

 Another agency has been the development of irrigation works. 



1 The Journal of the Royal Agricultural Society of England, vol. xxiv. 

 (second series), part 1. (John Murray, Albemarle Street.) 



