30 On the Solar Eclipse, 



either the extreme boundary of the periphery, or the line of 

 demarcation of any spot then visible upon the disc ; also that 

 the observation might commence from the appulse, either of 

 the summit or of the base of a mountain, according as its 

 situation was on the moon's eastern or western limb. 



It soon appeared, however, that only one of these methods 

 could be adopted in the present instance, and that several causes 

 concurred, during the early part of the eclipse, to impede the 

 application of the general principle in question. The observer 

 not being aware of its approach till the mountain had actu- 

 ally appeared, part of its height was passed over before he 

 could commence his observation ; from a similar cause, not 

 knowing in what particular point to expect the appulse, the 

 most favourable opportunities were altogether lost ; the inten- 

 sity of the solar light also being very little diminished, neces- 

 sarily obstructed investigations so minute. For these and other 

 reasons, it seemed most advisable to defer any farther attempt 

 till the eastern limbs of the two luminaries should come in 

 contact. Soon after the central conjunction, two eminences on 

 the moon's eastern circumference were accordingly selected 

 on account of their superior height and convenient situation, one 

 being detached, the other a precipitous termination of a ridge, of 

 which an exact outline is given in Fig. 1, Plate II. As had been 

 anticipated, the former obstructions were now in great measure 

 removed ; the observer could trace any particular projection 

 through every part of its course, and note the instant of ap- 

 pulse with the utmost accuracy. Of the two, forming the 

 principal subject of observation, that of which the figure is 

 given arrived at the edge of the solar disc some minutes be- 

 fore the other, and from the contact of the summit, till the 

 base attained the same point exactly 2" elapsed. In like 

 manner, the second was found to take nearly 2f" in passing; 

 2" 30" were assumed at the time, as a very near approximation 

 to the truth. Before their egress, the appearance of these 

 mountains was extremely beautiful, especially of the higher ; 

 on both sides of which, arcs of the sun's surface were visible, 

 becoming gradually narrower, and at length appearing like 



