232 



KNOWLEDGE 



[October 1, 189-i. 



where tlie caps for toy pistols were made. It was believed 

 that the explosion was owing to one of these nmoires, 

 containing more than the regulation amount of composition, 

 having been cut with scissors, and thus causing all the 

 rest to explode. The shed was wrecked, and three girls 

 lost their lives. A similar case happened in France, where 

 a child was killed by cutting open a cap, which caused two 

 large packets to explode. 



When an explosion is communicated from one cartridge 

 to another there is a gradually weakening effect This 

 was proved experimentally, in 1872, by Captain Miintz, at 

 Versailles. The explosion of the first charge excavated a 

 funnel-shaped hole in the ground measuring •'■) metre* 

 in diameter. The shock caused a second similar cartridge 

 placed at some distance to explode, but in this case the 

 diameter of the hole excavated was only -6(3 metre. 



Captain Colville found that there was a definite relation 

 between the weight of the charge used and the distance 

 between the cartridges. A charge weighing one kilogram, 

 and containino; seventy-five per cent, of dynamite, commu- 

 nicated its explosion on hard ground -3 metre. Where D 

 represents the distance in metres, and C the weight of the 

 charge in kilograms, he showed that under these conditions 

 D := 3 C. When the cartridges were laid on a rail, the 

 distance to which the explosion could be communicated 

 was increased, and D = 7 C. On the other hand, on soft 

 or ploughed earth the distances were much less. 



To explain this property of explosives. Sir Frederick 

 Abel advanced the attractive theory of a sympathetic 

 rhythmic vibration between the substance detonating 

 and that detonated, analogous to the synchronous vibra- 

 tions set up by sound waves. A certain note of a piano 

 will often cause a glass to jingle, and if the glass be made 

 to emit its note it will be found to be the same as the 

 note of the piano — that is, each vibrates at the same rate. 

 Sir Frederick Abel thus expresses his theory : " Vibrations 

 produced by particular explosions, if synchronous with 

 those which would result from the explosion of a 

 neighbouring substance, will, by their tendency to develop 

 those vibrations, either determine the explosion of that 

 substance or at any rate greatly aid the disturbing effect of 

 mechanical force suddenly applied." 



Facts in support of this are that sometimes a feeble 

 detonation will determine an explosion when a more 

 violent one will not. Thus iodide of nitrogen will not 

 cause compressed gun-cotton to explode, nor does nitro- 

 glycerine cause the explosion of gun-cotton in sheets on 

 which is placed the case of nitro-glycerine. 



The interesting experiments of Champion and Pelletf 

 tend, perhaps, to confirm this. 



1. A very small quantity of iodide of nitrogen, detonated 

 at one end of a long narrow tube, caused the explosion of 

 a similar quantity of the same substance placed at the 

 other end of the tube at a distance of seven metres. That 

 the transmitted concussion was slight was shown by. the 

 insertion of a light pith ball in the middle of the tube. 



2. Damp iodide of nitrogen was fixed to the strings of a 

 bass viol. When it was dry the strings of a similar 

 instrument were made to vibrate at a distance. A deto- 

 nation occurred only when a note giving sixty vibrations 

 per second was sounded. The G cord caused an explosion, 

 while the E cord did not. The vibrations produced by 

 metal plates acted in the same manner as strings. 



From these results the observers came to the conclusion 

 that explosion was due to vibratory motion independent of 

 heat and shock. 



This theory has not met with general acceptance. 



* A -raMre = 393 inches. t Compies rendus, LXXV. 



Eissler^ is strongly opposed to it. He urges that all the 

 experiments of Champion and Pellet may be explained by 

 taking into account the vibrations of the supports and the 

 resulting friction. Moreover, the characteristic feature of 

 a given note has never been established, but only the fact 

 that below a certain rate of vibration the explosive effect 

 ceases. He explains the facts by the supposition of 

 two orders of waves, one explosive and the other purely 

 mechanical. 



In substantial agreement with him. Berth elotj also 

 objects to the theory of sympathetic vibrations. He proves 

 that the chemical stability of matter is unaltered by merely 

 sonorous vibrations, even when the substances experi- 

 mented on are as unstable as ozone, which is so readily 

 changed into oxygen. Therefore, according to him, 

 sonorous waves cannot be the real agents in chemical 

 decomposition and explosion. His explanation is that 

 " explosive matter detonates, not because it transmits the 

 vibratory energy by vibrating in unison, but, on the 

 contrary, because it stops it and appropriates the energy." 

 With reference to Abel's experiments, he argues that if 

 gun-cotton can explode nitro-glycerine, why cannot nitro- 

 glycerine explode gun-cotton, assuming that the two 

 compounds vibrate in sympathy ; whereas this transforma- 

 tion of energy into work may be readily explained by a 

 difference in constitution. 



The same chemist made a large number of experiments 

 to determine the velocity of the explosive wave in the case 

 of different explosives. ' Long, narrow tubes, made of 

 lead, tin, or Britannia metal were used, and the rate of 

 propagation of disturbance through the tube measured. 

 He found this to depend on — (1) The diameter of the 

 tube; (2) the density of the explosive; (3) the resistance 

 of the material of the tube. The explosive wave from 

 compressed gun-cotton had a mean velocity of five thousand 

 two hundred metres per second in lead tubes, and of six 

 thousand metres per second in tin tubes. Liquid nitro- 

 glycerine gave results varying from one thousand and 

 seventy-eight to one thousand three hundred and eighty- 

 six metres per second ; while dynamite had a mean rate 

 of two thousand five hundred and forty-three metres per 

 second. It was found a matter of great difficulty to deto- 

 nate the nitro-glycerine in such narrow tubes. A curious 

 feature was, that whether the tubes were curved or straight, 

 the results obtained were substantially the same. 



GLOBULAR STAR CLUSTERS. 



By J. E. GoKE, F.R.A.S. 



THE term " globular cluster " has been applied to 

 those clusters of stars which evidently occupy a 

 space of more or less spherical form. Some of 

 these "balls of stars," as they have been called, 

 are truly wonderful, and are among the most 

 interesthig objects visible in the stellar heavens. Good 

 specimens of the class are, however, rather rare objects, 

 and there are not many in the northern hemisphere. 

 The most remarkable is that called " the Hercules cluster," 

 but known to astronomers as 13 Messier, it being No. 13 in 

 the first catalogue of remarkable '' nebuloe " formed by 

 Messier, the famous discoverer of comets. It was discovered 

 by Halley in 1714. Messier was certain that it contained 

 no stars ! This wonderful object lies between the stars 

 Zeta and Eta Ilerculis, nearer to the latter star. It may 

 be seen with a binocular or good opera-glass as a hazy 



X Modern High Sxploxives. § Le-i Mafierex Explotfve-t. 



]\ Comptes re-ndus, ICO, 314—320. 



