28 On Radiant Matter. 



for showing the phenomena now under illustration, and I am 

 able by this means to carry the exhaustion to much higher 

 degrees than I can get by mere pumping. Working with 

 aqueous vapour I can use phosphoric anhydride as an ab- 

 sorbent ; with carbonic acid, potash ; with hydrogen, palla- 

 dium ; and with oxygen, carbon, and then potash. The 

 highest vacuum I have yet succeeded in obtaining has been 

 the 1-20,000, oooth of an atmosphere, a degree which may 

 be better understood if I say that it corresponds to about 

 the hundredth of an inch in a barometric column three miles 

 high. 



It may be objected that it is hardly consistent to attach 

 primary importance to the presence of Matter, when I 

 have taken extraordinary pains to remove as much Matter 

 as possible from these bulbs and these tubes, and have suc- 

 ceeded so far as to leave only about the one-millionth of an 

 atmosphere in them. At its ordinary pressure the atmo- 

 sphere is not very dense, and its recognition as a constituent 

 of the world of Matter is quite a modern notion. It would 

 seem that when divided by a million, so little Matter will 

 necessarily be left that we may justifiably neglect the trifling 

 residue and apply the term vacuum to space from which the 

 air has been so nearly removed. To do so, however, would be 

 a great error, attributable to our limited faculties being unable 

 to grasp high numbers. It is generally taken for granted 

 that when a number is divided by a million the quotient 

 must necessarily be small, whereas it may happen that 

 the original number is so large that its division by a 

 million seems to make little impression on it. According to 

 the best authorities, a bulb of the size of the one before 

 you (13*5 centimetres in diameter) contains more than 

 1,000000,000000,000000,000000 (a quadrillion) molecules. 

 Now, when exhausted to a millionth of an atmosphere we 

 shall still have a trillion molecules left in the bulb a 

 number quite sufficient to justify me in speaking of the 

 residue as Matter. 



To suggest some idea of this vast number I take the 

 exhausted bulb, and perforate it by a spark from the induc- 

 tion coil. The spark produces a hole of microscopical 

 fineness, yet sufficient to allow molecules to penetrate and 

 to destroy the vacuum. The inrush of air impinges against 

 the vanes and sets them rotating after the manner of a 

 windmill. Let us suppose the molecules to be of such a size 

 that at every second of time a hundred millions could enter, 



