April 24, 1902] 



NA TURE 



59: 



of revolution about a vertical axis. The interest of the paper 

 centres round the determination of the curve from which the 

 positions of equilibrium are found. 



The properties of focal lines have always presented a certain 

 difficulty to the student of geometrical optics. In 1S44, Sturm 

 enunciated the theorem that all the rays constituting a small 

 pencil emanating from a luminous point will, after any number 

 of refractions, pass through two focal lines which are at right- 

 angles to each other and to the middle ray of the pencil. Now 

 if the refracting surfaces are surfaces of revolution on a common 

 axis on which the luminous point is situated, the rays after any 

 number of refractions will all intersect this axis, although it is 

 not at right angles to the middle ray. On the contrary, if a 

 screen be placed perpendicular to the middle ray at the point 

 where it meets the axis of revolution, it is easy to see experi- 

 mentally that the section of the pencil by this screen is approxi- 

 mately a figure of eight, not a straight line as Sturm's theorem 

 would appear to indicate. We are glad to find that this point 

 has been considered by M. H. Bouasse in a note contributed to 

 the Journal ile Physique for April, and his explanation should 

 help to clear up the obscurities which exist in the conventional 

 treatment of focal lines. 



Our present state of civilisation has of necessity resulted in 

 an annual increase in the amount of capital borrowed by man 

 from the store of energy accumulated by our earth in bygone 

 times, and the diversion of this capital to uses for which the 

 world's annual income of solar energy was formerly deemed 

 adequate. An instance of this tendency is afforded by the 

 experiments of Dr. Selim Lemstrom, of Helsingfors, on 

 the uses of electricity in stimulating the growth of cereals, 

 vegetables and other plants. A German translation of Dr. 

 Lemstrum's paper has now been issued by Dr. Otto 

 Pringsheim. The investigation seems to have been sug- 

 gested in the first instance by an attempt to connect the 

 luxuriant growth of plants in high latitudes with the 

 influence of electric currents associated with the Aurora Borealis. 

 The experiments showed that for plants growing on arable land 

 of medium quality an increase of 45 per cent, in the crops is 

 obtainable ; but the better the field is ploughed and cared for 

 the greater will be the increase. On poor soil the efifect is 

 trifling. Certain plants, such as peas, cabbages and turnips, 

 only lend themselves to electrical treatment after being watered. 

 It is, however, injurious to most, if not all, plants to submit 

 them to the influence of electricity in hot sunshine. In the 

 introduction. Dr. Pringsheim makes some estimate of the cost 

 of applying the method to agricultural purposes, and arrives at 

 the conclusion that it can be made to pay. A further suggestion 

 is that we have here an explanation of the needle-shaped leaves 

 of coniferous plants which are well adapted to facilitate the 

 passage of electricity, or, in common parlance, "attract 

 electricity." 



With the March number, the Electro-Chemist and Metallur- 

 gist %ta.tii its second volume in a new form. It is now issued as 

 a magazine instead of, as hitherto, in the form of a weekly paper, 

 and it must be admitted that its present style is much more suited to 

 its contents and to the fact that it is only published bi- monthly. 

 We wish the journal all success in its endeavour to concentrate 

 attention on a branch of science in which this country is particu- 

 larly behindhand. The present issue, amongst other interesting 

 articles, contains an account, by Mr. J. R. Crawford, of the 

 Crawford-Voelker electric lamp. This lamp has attracted con- 

 siderable attention during the past few months, and one or two 

 articles about it have appeared in the technical Press. There is, 

 however, reason to believe that the problem of its commercial 

 manufacture is not yet fully solved, but the experimental results 

 NO. 1695, VOL. 65] 



are very promising. The filament, which is run in a vacuum, is 

 composed of carbide of titanium, and is formed by baking in 

 the arc a carbon filament which has been impregnated with an 

 organic compound of titanium. An energy consumption of 2'5 

 watts per candle is claimed for a 200-volt lamp, which rises 

 after 1000 hours' run to 3-35 watts per candle, the candle power 

 falling in the same time from 16 to 13. This is a very much 

 better result than can be obtained from a carbon lamp, and puts 

 the Crawford-Voelker lamp almost on a level with the Nernst 

 lamp. If the simplicity of the lamp, which requires no pre- 

 heating, is taken into account, it ' will be seen that, for small 

 units at any rate, it is likely to prove superior to Nernst's inven- 

 tion. In the interests of the electric light user it is to be hoped 

 that the lamp will soon emerge from the laboratory stage of 

 development. 



The Society of Chemical Industry is gradually extending its 

 borders, and in time, no doubt, will embrace all divisions of 

 the English-speaking races. The New York Section, formed 

 in 1900, is already equal to the London Section of the Society in 

 numbers and importance, and Canadian and Australian Sections 

 are now being formed. The first meeting of the Canadian 

 Section was held on March 6, 1902, in Toronto, and was 

 favoured with a paper by Mr. B. E. F. Rhodin upon the new- 

 electrolytic alkali works at Sault Sainte Marie, Ontario. These 

 works were erected in 1900 to operate the Rhodin cell and process 

 for production of alkali and chlorine by electrolysis, and a portion 

 of the plant has been in use since early in 1901. The cell is of 

 the non-diaphragm mercury type, and differs from the better- 

 known Castner cell only in the mechanical means adopted for 

 producing circulation of the sodium amalgam and of the mercury 

 between the anodic and kathodic compartments of the cell. 

 The Rhodin cell cannot be wo rked in this country owing to litiga- 

 tion, w hich is still pending, relating to the validity of the Rhodin 

 patents, and the works in Canada represent the first industrial 

 application of the cell and process. The Canadian Electro- 

 Chemical Company are the owners of the works referred to, and a 

 decomposing plant of 120 cells, eijuivalent to a daily production 

 of 4i tons caustic soda and 9 tons bleach, has been erected at 

 Sault Sainte Marie. Three turbo-generators, each of 220 k.w., 

 have been installed, and these are driven by water from the St. 

 Mary's River, giving a head of 19 feet at the Power-house. 

 The works are not yet in full operation, as the commercial con- 

 ditions in Canada are not at present favourable for the sale of 

 the maximum output. It is hoped by the promoters of this 

 Company that at an early date the whole of the Canadian 

 requirements of caustic soda and bleach, will be met by the 

 production of the electrolytic process operated at Sault Sainte 

 Marie. 



We have received from Messrs. Friedlander, of Berlin, a copy 

 of " Natur.-E Novitates " for 1901, containing the usual valuable 

 lists of zoological literature. 



In the April number of the Zoologist a correspondent directs 

 attention to the probable duration of life in the great white 

 snail. A number of these were turned down at Blaxhall, 

 Suff'olk, in 1S82 and again in 1884, and as they do not appear 

 to have bred and some are still living, the inference is that the 

 survivors cannot be less than eighteen years of age, while some 

 are probably much older. 



At the auction rooms of Mr. J. C. Stevens on Thursday 

 last there was sold a portion of the collection of birds' eggs 

 formed by the late Mr. Philip Crowley, and containing a fine 

 series of British birds' nests with eggs, and also eggs from 

 another property. The three lots of chief interest were a fine 

 specimen of the Great Auk, 315/. ; an egg of the Great Auk, 

 252/. ; and a very fine specimen of the egg of the Great 

 -Epyornis, slightly cracked, 42/. 



