464 Intelligence and Miscellaneous Articles, 



terminals, the height of the shot above the sensitive plate could be 

 estimated. It seems to me that this method promises to be of 

 importance in the surgery of the extremities of the body ; for the 

 question whether to make an incision from the palm of a child's 

 hand or frcu the back of the hand is an important one. Stereo- 

 scopic pictures can also be obtained. 



The use of a Tesla coil in obtaining shadow pictures is advan- 

 tageous in certain respects, for by changing the size of the spark- 

 gap in the primary circuit of the Tesla coil one has a great range 

 of electrical energy at command. This range can be still further 

 increased by putting the spark-gap in a magnetic field. I have 

 taken such pictures iu less than a minute, showing the bones in 

 the fingers. The tubes were, at first, destroyed by disruptive 

 sparks over the surface of the tube which apparently penetrated 

 the glass between the platinum terminals and the glass. I have 

 lately discovered, however, that if the terminals of the tube are 

 placed in a vessel filled with paraffin oil, and if the oil is kept cool by 

 an outside vessel filled with snow or ice, the entire energy developed 

 by the Tesla coil can be employed, and the tubes are not destroyed. 



I have tried wooden lenses, both double convex and double 

 concave, in order to see whether the rays travel slower or faster 

 in wood than in air, but my results are negative. A copper ring 

 placed on a double convex lens of wood of approximately six inches 

 focus, and one also on a concave lens of the same radius as the 

 surfaces of the double convex lens, gave shadow pictures of the 

 ring which were of the same size and character as those of an 

 equal copper ring placed in air at the same distance from the 

 sensitive plate. 



"We naturally turn to Maxwell's great treatise on Electricity and 

 Magnetism, to see if a hint of this new phenomenon cannot be 

 found there : for I believe there is no manifestation of electro- 

 magnetism since the death of Maxwell which has not been 

 predicted or treated by him in one form or another in his 

 remarkable book. In section 792, vol. ii. of the treatise on 

 Electricity and Magnetism, he says: — "Hence the combined effect 

 of the electrostatic and the electrokinetic stresses is a pressure 

 equal to 2p in the direction of the propagation of the wave. Now 

 2p also expresses the whole energy in unit of volume. Hence in 

 a medium in which waves are propagated there is a pressure in 

 the direction normal to the waves, and numerically equal to the 

 energy in unit of volume. Thus, if in strong sunlight the energy 

 of the light which falls on one square foot is 83*4 foot-pounds per 

 second, the mean energy in one cubic foot of sunlight is about 

 0-0000000882 of a foot-pound, and the mean pressure on a square 

 foot is 0-0000000882 of a pound weight. A flat body exposed to 

 sunlight would experience this pressure on its illuminated side 

 only, and would therefore be repelled from the side on which light 

 falls. It is probable that a much greater energy of radiation 

 might be obtained by means of the concentrated rays of the 

 electric lamp. Such rays falling on a thin metallic disk, delicately 

 suspended in a vacuum, might perhaps produce an observable 

 mechanical effect." — American Journal of Science, March, 1896. 



