PRESENT PROBLEMS 99 



X-ray effects from explosions. High-grade gunpowder was loaded 

 by strong compression into rifle-shells designed for a 40-grain charge. 

 This powder was discharged from a heavy rifle, against an oak target 

 six inches from the muzzle of the gun. The target was faced with thin 

 plates of aluminum, which required frequent renewal. The concus- 

 sion was sufficient to extinguish a gas-flame seven feet from the line 

 of discharge. The plate used was one which would yield distinct 

 X-ray effects from an exposure of one second to a Crookes tube, 

 operated by an eight-plate Holtz machine. The dry plate was placed 

 behind the target, and was subjected to the discharge of twenty-five 

 pounds of powder, the operation requiring the spare time of the ex- 

 perimenter for forty days. The result was negative. No fluorescent 

 effects could be detected by an observer behind the target. A rapid- 

 fire gun might yield different results. 



The same experiment was made with a thousand copper shells 

 loaded with mercury fulminate. They were exploded in twos, one 

 being fired electrically, the other being exploded by the concussion. 

 The first shell was laid upon a wooden block resting on a two-inch 

 plank. The second shell, to be exploded by it, was laid upon it with 

 a heavy iron bolt-head just above. No metal was interposed between 

 the explosive and the photographic film beneath the plank, and it 

 was necessary to replace the block by a fresh one at each explosion. 

 These explosions were so violent that a photographic plate of glass 

 was shattered by the shock at almost every shot, and the windows 

 thirty feet distant were perforated by bits of copper which occasion- 

 ally escaped through the surrounding screens. A sensitive film of 

 gelatine was used, on which the shadow picture was expected, but 

 none was obtained. There is yet some reason to expect positive 

 results from experiments of this kind. It may well be that explosives 

 differ in this respect as in others. An investigation of the products 

 of such explosions by the electrical means now used in the study of 

 radioactive bodies is a wide and most inviting field, which is likely 

 to aid in the explanation of radioactive phenomena. 



Some of the products of explosion in the case of radium and 

 uranium are more nearly elementary in character than other bodies 

 yield, and some of the products are more elementary than others. 



Now there is nothing unusual in finding here and there a substance 

 which has some property to a very exalted degree. The diamond 

 is such a case. Iron is vastly more magnetic than any other substance. 

 All substances are magnetic. A group consisting of iron, cobalt, nickel, 

 etc., are more magnetic than the great body of substances, and iron 

 heads the list. There is nothing more remarkable in finding a group 

 of radioactive substances with one w r hich enormously surpasses all 

 others than there is in finding an Academy of Science with some 

 member surpassing all the others in some particular direction. 



