March 9, 1893J 



NATURE 



443 



bullet has turned, that a second bullet should be drilled 

 with a series of holes at about the corresponding position 

 differing very slightly from one another in angular 

 position, so that several would let the light through 

 and thus give a more accurate measure of the 

 rotation. 



There is a point of interest to sportsmen which has 

 given rise to a controversy which the spark photographs 

 supply the means of settling. The action of the choke bore 

 has been disputed, some having held that the shot are 

 made to travel more compactly altogether, while others, 

 while they admit that the shot are less scattered 

 laterally, as may be proved by firing at a target, assert 

 that they are spread out longitudinally, so that if this is 

 the case the improved target pattern is no criterion of 

 harder hitting, especially in the case of a bird flying 

 rapidly across the direction of aim. 



shot is filled with air waves of the greatest com- 

 plexity. They are not due to the cause already ex- 

 plained, but are, I believe, formed by the imperfect mixture 

 of air with powder gases still accompanying the shot. 

 The imperfect mixture of the two gases causes light to be 

 deflected in its passage, thus producing striae just as at 

 the first mixing of whisky and water, striae are seen 

 (sometimes attributed to oil !), which disappear when the 

 mixture is complete. I would mention, for the benefit of 

 any one who maybe 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 spark to pass. However, 

 by using thick copper 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 









Fig. 13. 



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 reasonable distance from the gun, but I 

 have taken comparative photographs at three or four 

 yards only 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 scattering at this short dis- 

 tance is not sufficient 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 ques- 

 tion of the kind by this method. The photograph, 

 Fig. 13, represents the shot from the cylindrical or 

 right-hand barrel. The velocity now is so low that 

 individual waves are no longer formed by each 

 shot. The whole space, however, occupied by the 



NO 12 19 VOL. 47 J 



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 liquid 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 I wish to conclude with a series of photo- 

 graphs which show how completely 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 unexpected nature are liable to appear when 

 making any new experiment. The result, however, is 

 otherwise of but little interest or importance. 



1 thought I should like to watch the process of the 



