MIRACLES OF SCIENCE 



ter visible under the microscope is greater by far 

 than the total human population of the globe since 

 the race developed. 



And a little instrument composed of two fragments 

 of gold leaf makes it possible to perform the miracle 

 of counting these denizens of the realm of infinite 

 littleness. 



SEEING THE INVISIBLE 



Moreover there is a second method, also devised 

 by Professor Rutherford, by which the helium atoms 

 may be counted as they fly off in the form of alpha 

 particles from radium ; a method that seems even 

 more wonderful than the other, because of its ex- 

 treme simplicity and the fact that it depends upon 

 direct vision. 



The method consists of watching through a micro- 

 scope a small portion of a screen covered with a 

 compound of sulphide of zinc or willemite. This 

 screen as originally devised by Professor Crookes, 

 has the property of emitting sparks of light when 

 bombarded by the alpha particles as they fly off from 

 a radioactive substance. As ordinarily witnessed the 

 bombardment suggests a shower of shooting stars; 

 or it may be even better likened to the splash of 

 raindrops on a dimly lighted pavement. The instru- 

 ment is called a sphinthariscope. 



Professor Rutherford adjusts a bit of radium near 

 the screen in such a way that all the rays are shut 

 off from it except those passing through a small 

 aperture. He can then through a microscope count 

 the splashes of light, each of which is 'due to the 



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