1870.] The Solar Eclipse of August last. 37 



essential to the success of the method, as there is everywhere on the 

 sun's limb sufficient depth of chromosphere to answer the purpose. 

 From the first photograph showing contact made by the Philadel- 

 phia party at the same place, Professor A. M. Mayer, who had 

 charge of that division, calculated the time of actual first contact, 

 and found that it came within two-tenths of a second of the record 

 made by Professor Young. 



Professor Young proposes to apply the spectroscope in this 

 manner to observations both of the external and internal contacts at 

 the next transit of Yenus. 



The partial-phase pictures show the various sun-spots visible at 

 the time (about six in number) with admirable definition, the larger 

 ones being surrounded by a marked fringe of faculae. They all show 

 a beautiful gradation of shade from the border of the sun inwards. 

 This shading of the source of light is due to the absorption of the 

 peripheral rays which necessarily pass through a greater thickness 

 of the dense solar atmosphere than those which emanate from the 

 central portion of the disc ; on a more searching examination of 

 the relative intensities of light of different portions of the solar 

 disc, there may be observed on all of these photographs, close to 

 the limb of the advancing or retreating moon, a bright glow like 

 that of early dawn, which extends from the moon to a distance of 

 about 15". Unless this glow can be accounted for in node and in 

 measure by diffraction, it would appear as if it were due to a lunar 

 atmosphere, although Dr. Mayer, in suggesting this explanation, 

 confesses that he cannot understand how an atmosphere capable of 

 producing such marked effects when projected against the intensely 

 lighted disc of the sun, should have no appreciable refractive effect 

 on small stars when occulted by the moon. We should be more 

 inclined to account for this glow as being the effect of specular 

 reflexion from the surface of the moon grazed by the sun's rays. 



A party under Professor Pierce devoted themselves exclusively 

 to the recording of that strange phenomenon, the corona. To 

 secure any impression from this object, which, notwithstanding its 

 apparent brightness, is remarkably deficient in photographic power, 

 it was necessary to make a very small image and to give a very 

 long exposure. 



The telescope was therefore arranged to produce an image in 

 its principal focus simply, and during the totality an exposure of 

 forty seconds was given. By this means a picture was obtained 

 of which the cut on the next page is a very careful copy. From the 

 long exposure, the motion of the moon, and probably also of the light 

 in the corona, there is little sharpness of definition, and the promi- 

 nences only appear as bright spots. The general shape of the 

 corona is, however, very well given, and the curious appearance of 

 curvature, in some parts, is very manifest. Professor Himes, who 



