ELECTRIC LIGHT 203 



vulcanised India-rubber tubing, of suitable length, and a tin tube, rather longer and 

 wider than the latter, were slipped on to the branch wire, before it was joined to the 

 fuze-wire, and, when the junction had been effected, the India-rubber tube was pulled 

 over it, and tied very firmly at both ends on to the gutta-percha covering of the wires, 

 fig. 789. A small quantity of a cement (consisting of bees' -wax and turpentine) was 



789 





rubbed in between the latter and the ends of the India-rubber tube, so as thoroughly 

 to ensure the exclusion of water, and finally the tin tube was pulled over the joint, 

 and fixed (by compressing the ends) for the purpose of imparting rigidity to the 

 junction, and thus protecting it from injury by any sudden twist or strain. By these 

 arrangements, when carried out with moderate care, the perfect exclusion of water 

 from the charge and from its connection with the branch wire was effected. 



The first trials of these charges were made in a shallow canal with a mud bottom, 

 and from which, at the time of experiment, the water was receding so rapidly, that 

 before the whole of the charges had been immersed, several of them were exposed to 

 view, being partly imbedded in the mud. Twenty-five charges were arranged, of 

 which thirteen were exploded, though less rapidly than in the experiments on land. 

 On the next occasion, when twenty-five charges were entirely surrounded by water 

 (simply resting upon the firm bed of a pond of some depth), only four of the charges 

 were exploded. Several other attempts were made to fire a smaller number of (ten 

 and five) charges similarly immersed, but in every instance only four were ignited. 

 A careful examination into the cause of the invariable explosion of so comparatively 

 limited a number of charges under water led to the following explanation : 



It will be remembered that the explosion of numerous charges in a divided circuit 

 by the magneto-electric apparatus with revolving armatures is effected by the action 

 of an exceedingly rapid succession of currents. The rapidity with which they 

 follow each other, however great, cannot equal that with which the terminals of a 

 fuze, enclosed in a small charge, under water, come into contact with the latter 

 after the explosion. The instant this occurs, a complete circuit is established through 

 the water, and any further action of the current is at once arrested. By the time, 

 therefore, that four charges had been ignited in extremely rapid succession, so as to 

 be apparently exploded at once, a sufficient interval of time had in reality elapsed to 

 allow the water to re-occupy the space filled for a brief period by the gaseous pro- 

 ducts of the first explosion, and thus to rush in upon, and complete the circuit with, 

 the terminals of the fuze. It appears probable that, with the employment of larger 

 charges of powder (about eight ounces was the quantity exploded in each charge) when 

 the volume of water displaced by the explosion would be more considerable, a great 

 number of charges would be exploded before the circuit could be completed by the water. 



ELECTRIC ZiZCHT. Various attempts have been made, from time to time, to 

 employ electricity as an illuminating power ; but hitherto without the desired success. 

 The voltaic battery has been employed as the source of electricity, and in nearly all 

 the arrangements, the beautiful arc of light produced between the poles, from the 

 points of the hardest charcoal, has been the illuminating source. One of the great 

 difficulties in applying this agent arises from the circumstance that there is a trans- 

 ference of the charcoal from one pole to the other, and consequently an alteration in 

 the distance between them. This gives rise to considerable variations in the intensity 

 and colour of the light, and great want of steadiness. Various arrangements, many 

 of them exceedingly ingenious, have been devised to overcome these difficulties. 



The most simple of the apparatus which has been devised is that of Mr. Staite, 

 which has been modified by M. Archereau. Two metal columns or stems, to which 

 any desired form can be given, are connected together by three cross pieces, so as to 

 form one solid frame ; one of these cross pieces is metallic, namely the one which occupies 

 the upper part of the apparatus ; the others must be of wood. These latter serve as 

 supports and points of attachment to a long bobbin placed parallel to the two columns 

 and between them, and which must be made of tolerably thick wire, in order that the 

 current, in traversing it without melting it, may act upon a soft iron rod placed in the 

 interior of the bobbin. This iron rod is soldered to a brass stem of the same calibre, 

 and of the same length, carrying at its free extremity a small pulley. On the opposite 

 side the iron carries a small brass tube, with binding screws, into which is introduced 

 one of the carbons, when the entire rod has been placed in the interior of the bobbin. 

 Then a cord fixed to the lower cross piece, and rolling over a pulley of large diameter, 

 is able to serve as a support to the moveable iron rod, running in the groove of the 



