53 TRANSACTIONS OF THE [NOV. 25, 



observer, who will swing a pendulum at various points for the 

 purpose of determining the value of gravity acceleration. Mr. 

 Preston accompanied the expedition to the Caroline Islands 

 some years ago. Naturalists and botanists are also with the 

 party ; and Prof. Agassiz may join the expedition and dredge 

 for deep-sea life near the coast. Should cloudy weather, there- 

 fore, make temporarily useless all the labor and pains spent on 

 the eclipse apparatus, there will be still some important scien- 

 tific results forthcoming. 



The reading of the paper was followed by a number of lantern 

 illustrations showing the appearances of the corona at various 

 eclipses, including the photograph taken by Prof. H. S. Pritch- 

 ett's party on January 1st, 1889. 



ADDITIONAL NOTES ON THE ECLIPSE OF DECEMBER, 1889. 



The total solar eclipse of December 22d, 1889, may be better 

 understood in its special features by a consideration of the follow- 

 ing figures: — 



The moon in general moves in her orbit very nearly 2,100 

 miles per hour. This would be the rate of shadow-motion, were 

 it not for the earth's rotation; but the rotation being to the east, 

 the shadow-motion is therefore retarded. The earth's surface 

 at the equator moves about 1,040 miles per hour. The motion 

 of the shadow, the moon being in the zenith, would be, at the 

 equator, the difference between 2,100 and 1,040, namely, 1,060 

 miles per hour. This is the slowest motion the shadow can have, 

 about equal to the speed of a cannon-ball. The velocity is much 

 greater than this at points north and south of the equator, 

 where the earth's rotation is linearly less, and where the shadow 

 falls very obliquely, as it does when an eclipse occurs near sun- 

 rise or sunset. The velocity, through these various causes, may 

 be exceedingly swift, as great as 4,000 or 5,000 miles per hour.' 



The eclipse of December 22d lasts, from the first instant that 

 the shadow strikes the earth to the moment when it leaves the 

 earth, 5h. 15.2m. The central eclipse lasts 3h. 23m., — that 

 is, it takes 3h. 23m. for the central shadow to move over the 

 earth. ^ The length of path of totality is about 9,250 miles; 

 hence, considering the motion as uniform, the central shadow 

 moves over the face of the waters at about 2,700 miles per hour. 

 The width of totality-path is variable, but on the average a lit- 



* Young's " General Astronomy," p. 237. 



^American Ephemeris and Nautical Almanac, 1889, p. 418. 



