158 DISCOVERY OH. 



clouds. He put his knuckles near the key, but obtained 

 no sparks. Again and again he tries to draw an electric 

 spark from the key, yet without success. Is his con- 

 jecture wrong and the experiment a failure ? No, the 

 rain has now wetted the twine and made it a better 

 conductor of electricity. Once more Franklin presents 

 a knuckle to the key, and a strong spark is the result. 

 He obtains a succession of sparks, and uses the electricity 

 from the clouds to produce the same effects as that 

 from man-made machines. He has established the 

 identity of lightning and electricity, and answered Job's 

 question, " Canst thou send lightnings, that they may 

 go, and say unto thee, ' Here we are ' ? " Facts were 

 at last available upon which a reasonable theory as to 

 the nature and origin of lightning could be based. 



Writers in the popular press, and in technical papers 

 also, frequently indulge in cheap sneers at what they call 

 " scientific theory." In their minds, the man of science 

 lives in a world far removed from the realities of life, 

 and knows little of material things or practical possi- 

 bilities. Nothing could be more incorrect than this 

 view. With the exception of pure mathematics and 

 metaphysics, every branch of physical and natural 

 science depends for its progress upon practical work in 

 the laboratory or the field. No one appreciates the 

 value of experimental work more than the man of 

 science, and no one is more critical of scientific theory. 

 Whenever a theory is put forward in scientific circles, 

 it is always subjected to severe attack from people most 

 competent to point out its weaknesses ; and in any case 

 it only survives until someone brings forward evidence 

 which disproves it. 



For example, Newton supported with the weight of his 

 great authority the theory that light is due to the 



