i66 THE POPULAR SCIENCE MONTHLY. 



sarily 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 induction-coil. The spark 

 produces a hole of microscopical fineness, yet sufficient to allow mole- 

 cules to penetrate and to destroy the vacuum. The inrush of air im- 

 pinges 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 million 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 ; sup- 

 posing 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 aj^pear, and the last man disappear ; supposing it to survive 

 until the fulfillment of the mathematicians' prediction that the sun, 

 the source of energy, four million centuries from its formation will 

 ultimately become a burned-out cinder ; * supposing all this — at the 

 rate of filling I have just described, one hundred million molecules a 

 second — this little bulb even then would scarcely have admitted its 

 full quadrillion of molecules, f 



But what will you say if I tell you that all these molecules, this 

 quadrillion of molecules, will enter through the microscopic hole be- 



* The possible duration of the sun from formation to extinction has been variously 

 estimated by different authorities at from eiahteen million years to four hundred million 

 years. For the purpose of this illustration I have taken the highest estimate. 



f According to Mr. Johnstone Stoney ("Philosophical Magazine," vol. xxxvi., p. 

 141), 1 c. c. of air contains about 1000,000000,000000,000000 molecules. Therefore, a 

 bulk 13-5 centims. diameter contains 13-53 >< 0-5236 X 1000,000000,000000,000000 or 

 1,288252,350000,000000,000000 molecules of air at the ordinary pressure. Therefore 

 the bulk, when exhausted to the millionth of an atmosphere, contains 1,288252,350000,- 

 000000 molecules, leaving 1,288251,061*747,650000,000000 molecules to enter through 

 the perforation. At the rate of 100,000000 molecules a second, the time required for 

 them all to enter will be — 



12882,510617,476500 seconds, or 



214,708510,291275 minutes, or 



3,578475,171521 hours, or 



149103,132147 days, or 



408,501731 years. 



