1 66 Master Minds of Modern Science 



3. That in two different places, three hundred miles 

 apart, the rays were exactly alike at the same heights. 



Still Dr Millikan was not content. There is no one more 

 thorough in his methods than the modern scientist. In 

 1926 fresh experiments were carried out in Lake Miguilla, 

 in Bolivia, a lonely tarn lying at a height greater than that 

 of the summit of Mont Blanc — that is, more than fifteen 

 thousand feet. 



• Professor C. T. R. Wilson had suggested that the rays 

 might be caused by the impact of electrons endowed with 

 many millions of volts of energy acquired in thunder- 

 storms. But such a lake as Miguilla is completely 

 screened from such effects, and the experiments there 

 definitely discredited Professor Wilson's theory. What is 

 more, the readings of the sunken electroscope gave results 

 similar to those achieved in North American lakes, thus 

 proving that the rays had equal power in both hemispheres 

 of our planet. 



In 1926 Dr Millikan and his assistants constructed 

 electroscopes more delicate than any that had yet been 

 made, and in the following year used these in two lofty 

 Californian lakes named Gem and Arrowhead. With 

 these electroscopes zero was not reached until the instru- 

 ment had been sunk to a depth of one hundred and 

 sixty-four feet, showing that the sensibility of the instru- 

 ment had been increased eightfold. Taking into account 

 the absorption of the rays by the atmosphere above Gem 

 Lake, the new experiments revealed rays so penetrating as 

 to pass through two hundred feet of water or eighteen feet of 

 lead before being completely absorbed. 



And now no doubt our readers will be wondering 

 whether these so-called ' cosmic ' rays have any signifi- 

 cance for the man in the street, or any special importance 

 in the working of the universe. 



The answer can best be given by Dr Millikan himself. 

 Speaking in 1928 before the California Institute of 



