Scientific Lectures. 269 



SCIENTIFIC LECTURE.— VI. 



ON THE CONSTITUTION OF THE SUN. 



By Dr. B. A. Gould op Cambridge, Mass. 



The lecture was profusely illustrated by photographs of the sun, 

 reflected with the aid of a lanteru upon a background of white cloth. 

 One of the photographs, showing spots and facul®, was taken only a 

 few hours before the meeting, by Mr. Lewis M. Rutherfurd, at his 

 observatory, and was pronounced by Dr. Gould an excellent one. 

 The lecturer was introduced by Prof. S. D, Tillman, Secretary of 

 the Institute. 



On coming forward, Dr. Gould was greeted with applause, and 

 spoke as follows : 



Ladies and Gentlemen. — It would be a vain task to attempt any 

 investigation of the history of our early astronomical knowledge of 

 the sun. Herodotus relates that Thales of Miletus predicted the 

 total eclipse, which occurred in the year 584 B. C, during the sixth 

 day of a battle between the Medes and Lydians, and which by its 

 awe-inspiring influence brought their five years' war to a close. We 

 know, too, that Pythagoras and his immediate pupils taught the 

 doctrine, which he probably learned in Egypt, where he had studied, 

 that the sun is the center of the universe, and that the earth revolves 

 around him once a year. Three and a half centuries later, Archi- 

 medes correctly determined the sun's apparent diameter as between 

 27' and 33'. 



The determination of the earth's distance from the sun is a prob- 

 lem of peculiar importance, inasmuch as it is t.ie unit in which, by 

 means of Kepler's laws, all the planetary distances are measured. 

 Consequently, all our knowledge of celestial distances (excepting 

 only that of the moon) is closely connected with the value of tiiis 

 fundamental standard of measures; and any addition to our know- 

 ledge, which shows any one adopted distance to be too large or too 

 small, deinonstrntes the same for all the rest. This determination is 



