LIGHT AND ITS ARTIFICIAL PRODUCTION. 281 



penetrating flesh about a hundred times more easily than bones or 

 metallic substances, aluminum excepted, and in this they have found 

 their widest application. We can not help admiring this wonderful 

 quality, whether the rays are an entirely new kind of longitudinal 

 ether waves, or whether, as is more probable, they are merely trans- 

 verse ether waves just like ordinary light waves, although of a very 

 minute wave length, so that they may easily pass between the mole- 

 cules of substances of moderate density. Let us rejoice that they 

 have helped suffering mankind in their application to surgery, and let 

 us hope that they will point out to science new lines of investigation. 

 In all these experiments the electric current of the Euhmkorfif coil was 

 conducted directly through the electrodes into the interior of the 

 exhausted tube. If alternating electric currents of millions of alter- 

 nations per second are used, so-called electrical oscillations such as are 

 produced by the discharge of a Leyden jar or condenser, the Geissler 

 tube shines brightly even if it is only held near the wire without any 

 metallic connection whatever with it. The name of Nicola Tesla, an 

 American, will be permanently associated with these phenomena, since 

 he was the first to carry out experiments in this field on a large scale. 

 The light effects produced by "electrical oscillations" are especially 

 distinguished in that by means of them nearly the whole of the elec- 

 trical energy supplied is transformed into light. H. Ebert conducted 

 high frequency currents of a definite periodicity to a tube in the inte- 

 rior of which a specially selected fluorescent substance was placed. 

 By the fluorescence produced by the cathode rays he obtained a lumin- 

 osity of about one-thirtieth of a Hefner unit by an expenditure of one- 

 millionth of a watt. The total energy consumed was about one-two- 

 thousandth of that of a Hefner lamp. We have here realized very 

 nearly an ideal artificial illumination, and with justice Ebert calls his 

 lamp "the lamp of the future," although, on account of the technical 

 difficulties involved and tbe small luminosity, it may be a long time 

 before these lamps will be able to compete with those now used. 



LUMINOSITY DUE TO HIGH TEMPERATURES. 



The transition from luminosity at low to that at high temperatures is 

 found in the ghost-like glowing observed in the dark during the slow 

 oxidization of some substances — for example, phosjjhorus. This action 

 is not really a combustion. Oxidation and combustion are essentially 

 similar to each other; in both there is a combination of the substance 

 with oxygen. But while the oxidation can take place at relatively low 

 temperatures, ignition and combustion occur only at relatively high 

 temperatures. 



The development of heat from light which takes place in every fire, 

 in every freely-burning flame, in a candle, a lamp, etc., is therefore 

 nothing more than an oxidation or combustion ; that is, the combination 

 of a substance with oxygen at a high temperature. 



