160 /Scientific Intelligence. 



in oil. When this method is applied to a hollow target tube the 

 fresh, cool oil must be made to constantly strike against the back 

 of the target, otherwise this will get red hot and drive back the 

 oil, the hydrogen passing through the platinum. In this way I 

 have had the vacuum change from fifteen inches to one-sixteenth 

 of an inch equivalent air-spark in a short time. 



What those of us who are trying to use Rontgen's discovery 

 in medical diagnosis want, is not rediscoveries, but to have placed 

 within our reach apparatus which will convert into Rontgen light 

 an appreciable amount of the energy put into it. At present we 

 may pour in at one end energy at the rate of ten amperes at one 

 hundred volts, and when we come to take it out at the other end 

 as Rontgen radiation there will not be enough with good defini- 

 tion to clearly see through the abdomen. If some broad commer- 

 cial use could be found for Rontgen's discovery, then the great 

 inventors would attack the problem. At present a tallow candle,, 

 notwithstanding its thermic waste, is as a converter of energy 

 into light a shining success compared with the best available 

 Rontgen apparatus. The only notable advance which has been 

 made in practice is due to M. Tesla, but even he seems unable to 

 give much time to this matter ; as a result, neither he nor anyone 

 knows when his apparatus will be commercially available. Even 

 when we get it the results will probably be far below the possi- 

 bilities of the method as shown by the hints dropped from time 

 to time by prominent physicists. Take, for example, Professor 

 Trowbridge's statement that he had made a photograph of the 

 bones of a hand in one-millionth of a second. With the best 

 available apparatus the exposure must be from sixty million to 

 three hundred million times as long. Part of the advance which 

 will be made must consist in devising simple means of making 

 the exciting surges harmonics of the rate of vibration we wish to 

 produce in the radiant energy. All my experiments point in this 

 direction, and I find it practical to get a better result with a 

 small properly-tuned generator than with the largest size improp- 

 erly adjusted, but I know too little of physics to make any impor- 

 tant advance in this matter. 



II. GrEOLOGY AND NATURAL HISTORY. 



1. The Age of the Earth. — The January number of the Philo- 

 sophical Magazine contains a notable article by Lord Kelvin, 

 on the age of the earth as an abode fitted for life. This is an 

 extension of the Victoria Institute Annual Address for 1897. The 

 opening pages give an interesting account of the early attitude 

 of the geologist to the subject in demanding almost unlimited 

 time for the geological changes the earth has gone through and 

 for the development of life. Then follows a summary of the 

 arguments by which the author showed (1862 to 1869) the strict 

 limitations of the possible age of earth, viewed as an abode for 

 life, and arrived at the conclusion that the earth's consolidation 



