ELECTRONIC THEORY OF ELECTRICITY. n 



unit of weight equal to one billionth of one billionth of a gram, 

 and then on this scale the hydrogen molecule weighs 10 such units. 

 We may obtain in another way an illustration of the mass size and 

 number of the molecules of any gas in the following manner : 



First as to size. We can in a good Whitworth measuring instru- 

 ment detect a variation in length of a metal bar equal to one millionth 

 of an inch. This short length would be occupied by 25 molecules 

 placed in a row close together. We can in a good microscope see a small 

 object whose diameter is one hundred-thousandth of an inch. In 

 a small box of this size we could pack 16 million molecules close 

 together. The smallest weight which can be weighed on a very good 

 chemical balance is one hundredth of a milligram. The united 

 weight of one million million million molecules of hydrogen would 

 therefore just be detectable on such a balance. 



Ultra-Atomic Matter. 



Until a few years ago our knowledge of the divisibility of matter 

 may be said to have ended with the chemical unit, the atom. But 

 of late years information has been steadily accumulating which has 

 made us acquainted with matter in a finer state of subdivision. For 

 a long time a controversy was carried on, whether the radiation in a 

 high vacuum tube which proceeds from the kathode was a material 

 substance or a wave motion of some kind. But no fact yet found is 

 inconsistent with the notion which originated with Sir William 

 Crookes that the transfer which takes place is that of something which 

 has the inertia quality of matter, and his term • radiant matter' is a 

 peculiarly suitable phrase to describe the phenomena. The great ad- 

 vance which has since been made, by Professor Thomson and others, 

 is that of measuring accurately the amount of bending which a 

 stream of this radiant matter experiences under a known magnetic 

 force and from this deducing the ratio between the mass of the radiant 

 particle and the electric charge carried by it. This measurement shows 

 that if the radiant matter consists of corpuscles or particles, each 

 of them carries a charge of one electron, but has a mass of about one 

 thousandth of a hydrogen atom. 



The evidence therefore exists that Crookes' 'radiant matter' also 

 called the 'kathode rays' and Thomson's 'corpuscles' are one and the 

 same thing and that these corpuscles may be described as fragments 

 broken off from chemical atoms and possessing only a small fraction 

 of their mass. These particles are shot off from the negative terminal 

 or kathode of the vacuum tube with a velocity which is from one fifth 

 to one third the velocity of light. 



Moreover it has been shown that when the kathode rays pass 

 through a thin metal window in a vacuum tube and get into the space 



