THE VACUUM THERE S SOMETHING IN IT WHITNEY 195 



workman who keeps his drink hot or cold in a thermos bottle is 

 clearly indebted to Sir James Dewar's application of the vacuum, 

 but the scientist is still more indebted to it. All our steam-power 

 plants, including turbines, owe their success to vacua. 



The latest arrival in the family of the chemical elements (haf- 

 nium) was discovered by trying it in vacuum as an X-ray target. 

 Our list of possible chemical elements was rounded off by Moseley's 

 study of the X-ray spectra just in time to meet the wonderful dis- 

 coveries of J. J. Thomson and Aston, all made in vacua. The latter 

 showed that most of the elements, supposedly simple, are still mix- 

 tures of two or more similar elements (isotopes), while Professor 

 Thomson's experiments disclosed by the positive ray method a 

 whole series of new atomic compounds. 



While the vacuum was not essential to the work of Millikan m 

 isolating the electron, yet the earlier work by Thomson and others 

 and much of the recent work on this ultimate constituent of matter 

 has been necessarily carried out in vacuum. To-day there seems 

 to be no end to the studies which can be based on the fact that an 

 atom or molecule of material may be separated electrically into a 

 positively charged ion (carrying most of the mass) and a negatively 

 charged electron (carrying most of the current). 



ELECTRICITY 



Without sacrificing historical truth too much, it may be asserted 

 that electricity at rest was the first kind known. It then seems logi- 

 cal that electricity in simple direct motions should later appear and 

 that still later we should find various directions and rates of its 

 motion, if it moves at all. It will interrupt this line of argument if 

 we doubt the existence of electricity as a thing or question the exist- 

 ence of such different kinds of it as static and dynamic. The elec- 

 tricity of rubbed amber was the first and stationary kind (if it is 

 admitted that prior to Thales such things as lightning were some- 

 thing else). When electricity first moved through metals the process 

 was looked upon as a simple directed flow which proceeded until the 

 charged body had delivered its charge. 



CURRENTS 



This direct flow of electricity (a current) was strengthened in its 

 hold on our conception by the great number of different chemical 

 current producers which followed the controversies betw^een Gal- 

 vani and Volta a century and a quarter ago. Primary and secondary 

 or storage batteries without number were soon discovered. The cur- 

 rent from such batteries was exactly like that which the magneto- 

 electric machines produced, when these were developed, after Fara- 

 day had shown the effect of moving a wire through a magnetic field. 



