636 
British Association . 
[September, 
trillion molecules left in the bulb. To suggest some idea 
of this vast number he perforated an exhausted bulb by a 
spark from the induction coil. The spark produced a hole 
of microscopical fineness, yet sufficient to allow molecules 
to penetrate and to destroy the vacuum. The inrush of air 
impinged against the vanes and set them rotating after the 
manner of a windmill. “ Let us suppose,” said Mr. Crookes, 
“ the molecules to be of such a size that at every second of 
time a hundred millions could enter. How long, think you, 
would it take for this small vessel to get full of air ? An 
hour? A day? A year? A century? Nay, almost an 
eternity ! A time so enormous that imagination itself can- 
not grasp the reality. Supposing this exhausted glass bulb, 
indued with indestructibility, had been pierced at the birth 
of the solar system ; supposing it to have been present when 
the earth was without form and void ; supposing it to have 
borne witness to all the stupendous changes evolved during 
the full cycles of geologic time, to have seen the first living 
creature appear, and the last man disappear ; supposing 
it to survive until the fulfilment of the mathematicians’ pre- 
diction that the Sun, the source of energy, four million 
centuries from its formation will ultimately become a burnt- 
out cinder ; supposing all this, — at the rate of filling I have 
just described, 100 million molecules a second, — this little 
bulb even then would scarcely have admitted its full quad- 
rillion of molecules.* But what will you say if I tell you 
that all these molecules, this quadrillion of molecules, will 
enter through the microscopic hole before you leave this 
room ? The hole being unaltered in size, the number of 
molecules undiminished, this apparent paradox can only be 
explained by again supposing the size of the molecules to 
be diminished almost infinitely — so that instead of entering 
at the rate of 100 millions every second, they troop in at a 
rate of something like 300 trillions a second. I have done 
the sum, but figures when they mount so high cease to have 
* Mr. Johnslone Stoney has shown (Phil. Mag., vol. xxxvi., p. 141) that 1 c.c. 
of air contains about 1000,000000,000000,000000 molecules. Therefore a bulb 
13*5 centims. diameter contains 13*5 3 xo‘5236x 1000,000000,000000,000000 or 
1,288252,350000,000000,000000 molecules of air at the ordinary pressure. 
Therefore the bulb when exhausted to the millionth of an atmosphere contains 
1,288252,350000,000000 molecules, leaving 1,288251,061747,650000,000000 
molecules to enter through the perforation. At the rate of 100,000000 mole- 
cules a second, the time required for them all to enter will be 
12882,510617,476500 seconds, or 
214,708510,291275 minutes, or 
3»57^475> I 7 I 5 21 hours, or 
149103,132147 days, or 
408,501731 years, 
