Auvttit 24, 18S2] 



NA TURE 



399 



of the temperature of explosion of gun-cotton showed it to be 

 about doable that of the explosion of gunpowder. One of the 

 effects observed to be produced by this sudden enormous de- 

 velopment of heat was the covering of the inner surfices of 

 the steel explosion-vessel with a net-work of cracks, small por- 

 tions of the surface being sometimes actually fractured. 1 he 

 explosion of charges of gun-cotton up to 2 '5 kilos in perfectly 

 closed chambers, with development of pressures approaching to 

 50 tons on the square inch, constitutes aljne a perfec.ly novel 

 feat in investigations of this class. 



Messrs. Noble and Abel are also continuing their researches 

 upon fired gunpowder, being at present occupied with an 

 inquiry into the influence exerted upon the chemical metamor- 

 phosis and ballistic effects of fired gunpowder by variation in its 

 composition, their attention being direc ed especially to the dis- 

 covery of the cause of the more or less considerable erosion of 

 the interior surface of guns produced by the exploring charge — 

 an effect which, notwithstanding the application of devices in 

 the building up of the charge specially directed to the pre> erva- 

 tion of the gun's boie, have become so serious that, with the 

 enormous charges now used in our heavy guns, the erosive 

 action on the surface of the bore produced by a single round is 

 distinctly perceptible. As there appeared to be prima facie 

 reasons why the erosive action of powder upon the surface of 

 the bore at the high temperatures developed should be at any 

 rate in part due to its one component sulphur, Noble and Abel 

 have made comparative experiments with powders of u'ual com- 

 position and with others in which the proportion of sulphur was 

 considerably increased, the extent of erosive action of the 

 products escaping from the explosion vessel under high tension 

 being carefully determined. With small charges a particular 

 powder containing no sulphur was found to exert very little 

 erosive action as compared with ordinary cannon powder ; but 

 another powder, containing the maximum proportion of sulphur 

 tried (15 per cent.), was found equal to it under these conditions, 

 and exerted very decidedly less erosive action than it, when 

 larger charges were reached. Other important contributions to 

 our know ledge of the action of fired gunpowder in guns, as well 

 as decided improvements in the gunpowder manufactured for the 

 very heavy ord.iance of the present day, may be expected to 

 result from a continuance of these investigations. Prof. Carl 

 Himly, of Kiel, having been engaged upon investigations of a 

 similar nature, has lately proposed a gunpowder in which hydro- 

 carbon- precipitated from solution in naphtha take the place of 

 the charcoal and sulphur of ordinary powder, this powder has 

 amongst others the peculiar property ol completely resisting the 

 action of water, so that the old caution, " Keep your powder 

 dry," may hereafter be unnecessary.; 



The extraordinary difference of condition, before and after its 

 ignition, of such matter as constitutes an explosive agent leads 

 us up to a consideration of the aggregate state of [matter under 

 other circumstances. As early as 1776 Alexander Volta observed 

 that the volume of glass was changed under the influence of 

 electrification, by w hat he termed electrical pressure. Dr. Kerr, 

 Govi, and others have followed up the same inquiry, which isat 

 present continued chiefly by Dr. George Quincke, of Heidelberg, 

 who finds that temperature, as well as chemical constitution of 

 the dielectric under examination, exercises a determining influ- 

 ence upon the amount and character of the change of volume 

 effected by electrification ; that the change of volume may under 

 certain circumstances be effected instantaneously as in flint glass, 

 or only slowly as in crown glass, and that the elastic limit of 

 both is diminished by electrification, whereas in the case of mica 

 and of guttapercha an increase of elasticity takes place. 



Still greater strides are being made at the pre-ent time towards 

 a clearer perception of the condition of matter when particles 

 are left some liberty to obey individually the forces brought to 

 bear upon them, by the discharge of high tensijn electricity 

 through tubes containing highly rarefied gases (Gcissler's tubes), 

 phenomena of discharge were produced which were at once 

 most striking and suggestive. The Sprengel pump afforded a 

 means of pushing the exhaustion to limits which had formerly 

 been scarcely reached by the imagination. At each step the 

 condition of attenuated matter revealed varying properties when 

 acted upon by electrical discharge and magnetic force. The 

 ladiometer of Crookes imported a new feature into these in- 

 quiries, which at the present time occupy the attention of leading 

 physicists in all countries. 



The means usually employed to produce electrical dis- 

 charge in vacuum tubes was Kuhmkorff's coil ; but Mr. Gassiot 



first succeeded in obtaining the phenomena by means of a 

 galvanic battery of 3000 Leclanche cells. Dr. De La Kue, in 

 conjunction with his friend Dr. Hugo Miiller, has gone far 

 beyond his predecessors in the production of batteries of high 

 potential. At his lecture "On the phe. omena of electrical 

 discharge," delivered at the Royal In-titution in January 1881, 

 he employed a battery of bis invention consisting of 14,400 cells 

 (14,832 Volts), which gave a current of 0-054 Ampere, and 

 produced a discharge at a distance of o 71 inch between the 

 terminals. During last year he increased the number of cells to 

 15,000 (15,450 Volts), and increased the current to 04 Ampere 

 or eight times that of the battery he used at the Royal Insti- 

 tution. 



With the enormous potential and perfectly steady current at 

 his disposal, Mr. De La Rue has been able to c attribute many 

 interesting facts to the science of electricity. He bas shown, 

 for example, that the beautiful phenomena of the stratified dis- 

 charge in exhausted tubes are but a modification an! a magnifi- 

 cation of those of the electric arc at ordinary atmospheric pres- 

 sure. Photography was u-ed in his experiments to record the 

 appearance of the discharge, so as to give a degree of precision 

 otherwise unattainable in the comparison of the phenomena. He 

 has shown that between two points the le.gth of the spark, pro- 

 vided the insulation of the battery is efficacious, is as the 

 square of the number of cells employed. Mr. De La Rue's 

 experiments have proved that at all pressures the discharge in 

 gases is not a current in the ordinary acceptation of the term, 

 but is of the nature of a disruptive discharge. Even in an appa- 

 rently perfectly steady discharge in a vacuum tube, when the 

 strata as seen in a rapidly revolving mirror are immovable, he 

 has shown that the discbarge is a pulsating one ; but, of course, 

 the period must be of a very high order. 



At the Royal Institution, on the occasion of his lecture, Mr. 

 De La Rue produced, in a very Urge vacuum tube, an imitation 

 of the aurora borealis ; and he has deduced from his experi- 

 ments that the greatest brilliancy of aurora displays must be at 

 an altitude of from thirty-seven to thirty-eight miles — a conclu- 

 sion of the highest interest, and in opposition to the extravagant 

 estimate of 281 miles at which it had been previously put. 



The President of the Royal Society has made the phenomena 

 of electrical discharge his study fur several years, and resorted 

 in his important experiments to a special source of electric power. 

 In a note addressed to me, Dr. Spottiswoode describes the nature 

 of his investigations much more clearly than I could venture to 

 give them. He says : "It had long been my opinion that the 

 dissymmetry shown in electrical discharges through rarefud 

 ga^es must be an essential element of every disruptive discbarge, 

 and that the phenomena of stratification might be regarded as 

 magnified images of features always present, but concealed under 

 ordinary circumstances. It was with a view to the study of this 

 question that the researches by Moulton and myself were under- 

 taken. The method chiefly used consisted in introducing into 

 the circuit intermittence of a particular kind, whereby one 

 luminous discharge was rendered sensitive to the approach of a 

 conductor outside the tube. The application of this method 

 enabled us to produce artificially a variety of phenomena, in- 

 cluding that of stratification. We were thus led to a series of 

 conclusions relating to the mechani-m of the discharge, among 

 which the following may be mentioned : — 



1. That a stria, with its attendant dark space, forms a physical 

 unit of a striated discharge ; that a striated column is an aggre- 

 gate of such units forme 1 by means of a step-by-step process ; 

 and that the negative glow is merely a locali ed stria, modified 

 by local circumstances. 



2. That the origin of the luminous c .lumn is to be sought for 

 at its negative end ; that the luminosity is an expre-sion of a 

 demand for negative electricity ; and that the dark spaces are 

 those regions where the negative terminal, whether metallic or 

 gaseous, is capable of exerting sufficient influence to prevent such 

 demand. 



3. That the time occupied by electricity of either name in tra- 

 versing a tube is greater than that occupied in traversirg an equal 

 length of wire, but less than that occupied by molecular streams 

 (Crooke's radiations) in traversing the tubes. Also that, espe- 

 cially in high vacua, the discharge from the negative terminal 

 exhibits a durational character not found at the positive. 



4. That the brilliancy of the light with so little heat may be 

 due in part to brevity in the duration of the discharge ; and that 

 for action so rapid as that of individual discharge-, the mobility 

 of the medium may count as nothing ; and that for these infini- 



