92 Master Minds of Modern Science 



for the new planet from Greenwich, but at that time the 

 best telescope at Greenwich was an equatorial of only 

 six and three-quarter inches aperture, housed in a very 

 small and inconvenient dome, an instrument quite un- 

 fitted for the work. 



At present there is no lack of fine telescopes at Green- 

 wich. The difficulty is that our climate is a very poor one 

 for astronomical observation. According to our records, 

 we have only one hundred and forty-one fine days out of 

 the three hundred and sixty-five. That is why most 

 of the great discoveries in modern astronomy have been 

 made either in North America or South Africa. As Sir 

 Frank Dyson said to the writer, the climate of the Pacific 

 slope is almost ideal for observation of the heavens, while 

 an observatory such as that of Mount Wilson has the 

 additional advantage of being built sufficiently high (five 

 thousand seven hundred feet) to be above mist, fog, and 

 low-lying cloud. 



Another advantage enjoyed by the American astrono- 

 mers is the possession of telescopes of a size and power 

 unknown elsewhere. These have been given by men of 

 enormous wealth such as Carnegie and Yerkes. At Mount 

 Wilson is the largest telescope in the world. It is a 

 gigantic reflector one hundred inches across. The mirror 

 is thirteen inches thick and weighs four and a half tons. 

 The moving parts of this telescope weigh one hundred 

 tons, and are driven by a powerful clock mechanism when 

 following the sun or stars. 



It must be remembered that the rapid movement of 

 the earth has to be counteracted if a telescope is to re- 

 main focused on one particular part of the heavens. 



The Mount Wilson telescope resembles a great naval 

 gun, and is in a revolving dome of one hundred feet 

 diameter. This telescope is about two and a half times 

 more powerful than the sixty-inch which was previously 

 the largest in existence, and has achieved important 



