MODERN VIEWS AND PROBLEMS OF PHYSICS. 519 



cording to their periods and amplitudes ; but these, instead of being 

 available in any particular form, are always more or less complex. 

 If we could produce waves of just the rate and amplitude we de- 

 sire, without any others in combination, a great step would be 

 gained. Then we could produce light without wasting at the 

 same time a great amount of energy in producing heat which we 

 do not want. This is one of the subordinate problems awaiting 

 solution. If to the production of such waves as are wanted we 

 could add a means of recording and fixing them in their true rela- 

 tive proportion, we would have the solution of another great ' and 

 fascinating subordinate problem the exact reproduction of natu- 

 ral scenes in color. A long step has been taken toward accom- 

 plishing the first of these achievements in the remarkable experi- 

 ments by Mr. Tesla with alternating electrical currents of high 

 frequency and high potential. Among the startling facts brought 

 out in these experiments is that although a current of electricity, 

 either direct or alternating, from ordinary dynamos under fifteen 

 hundred or two thousand volts electro-motive force will kill, yet 

 under alternations of a million to a million and a half per second. 

 a voltage of fifty thousand produces no shock or injury. Electric 

 lamps light with but a single wire leading to them. Vacuum 

 tubes become luminous in a properly prepared room with no 

 wires, and it is not extravagant, in view of what has already ap- 

 peared, to predict a future when unlimited power will be avail- 

 able at every man's hand. That will be when, as Mr. Tesla says, 

 we are able to " hook our machinery to the machinery of Nature." 

 In the conclusion of his lecture before the Institution of Electrical 

 Engineers, London, after describing a plan by which he thinks it 

 would be practicable to telephone across the Atlantic, he adds : 

 " But such cables will not be constructed, for, ere long, intelli- 

 gence transmitted without wires will throb through the earth 

 like a pulse through a living organism. The wonder is that, with 

 the present state of knowledge and the experience gained, no at- 

 tempt is being made to disturb the electrostatic or magnetic con- 

 dition of the earth, and transmit, if nothing else, intelligence." It 

 is probable that this wonder will give place to a still greater at no 

 distant period, by reason of successful attempts of just the kind 

 here mentioned. The problem is already in course of solution, 

 the distinguished electrician, Mr. Preece, having recently suc- 

 ceeded in sending telephonic messages over a circuit which was 

 wholly disconnected from that in which the generator was placed, 

 and at a distance of three miles from it. 



Unquestionably one of the most powerful aids to investigation 

 of late has been photography. Both as a science and as an art it 

 has grown in precision, speed, and availability, until now it has 

 become a weapon of attack as well as a means of record. While 



