180 ELECTRIC-SPARK PHOTOGRAPHS. 



teiioii of harder liittiug, especially in the case of a^ bird flying rapidly 

 across the direction of aim. 



I was unfortunately not able, in the limited space and time that I 

 have been able to employ, to take photographs of the shot at a i-easou 

 able distance from the gnu, but I have taken comparative photographs 

 at three or four yards ouly in which every shot is clearly defined, and 

 in which it is even easy to see on the negative where the shot have 

 been jammed into one another and dented. The difference in the scat- 

 tering at this short distance is not sufticient for the results to give any 

 information beyond this, that shot are as easily photographed as bullets, 

 and that no difficulty need be apprehended in attempting to solve 

 any question of the kind by this method. The j)hotograph, Plate ix, 

 represents the shot from the cylindrical or right-hand barrel. The 

 velocity now is so low that individnal waves are no longer formed by 

 each shot. The whole space however occupied by the shot is tilled 

 with air waves of the greatest complexity. They are not due to the 

 cause already explained, but are, I believe, formed by the imperfect 

 mixture of air with powder gases still accompanying the shot. The 

 imi^erfect mixture of the two gases causes light to be deflected in its 

 passage, thus producing strite, just as at the first mixing of whisky 

 and water striie are seen (sometimes attributed to oil!), which disap- 

 l^ear when the mixture is com[)lete. I would mention, for the benefit 

 of any one who nmy be tempted to continue these experiments, that a 

 pair of wires (such as are found to do so well when bullets have to be 

 caught) are not suitable, as one is sure to be shot away before such a 

 bridge of shot is made between them as will allow a si)ark to pass. 

 However, by using thick copi)er wires, one bent in the form of a screw, 

 with the other along the axis, no such failure can occur, and every shot 

 that I have taken in this way has been successful. One can of course 

 test the action of any material mixed with the shot. For instance, in 

 one case I mixed a few drops of li(piid oil with the shot and found them 

 more widely scattered in consequence, not, as has been stated, held 

 together by the oil as if they were in a wire cartridge. Of course, solid 

 grease or fat may, and no doubt does, produce such a result, but liquid 

 oil certainly does not. 



And now 1 wish to conclude with a series of photographs which show 

 how conq)letely the method is under control, how information of a kind 

 that might seem to be outside the reach of experiment may be obtained 

 from the electric-spark photograph, and how phenomena of an unex- 

 pected nature are liable to appear when making any new experiment. 

 The result however is otherwi.se of but little interest or importance. 



I thought I should like to watch the process of the piercing of a glass 

 plate by a bullet from the first shock step by step, until the bullet 

 had at last emerged from the confnsion it had created. ■ In Plate x, 

 the glass plate is seeu edgeways jiist after the bullet has struck it. 

 It is clear at once that the splash of glass dust backwards is already 



