352 I'HILOSOPHrCAL TRANSACTIONS. [anNO 1794. 



order to see whether any appearances would arise that might deserve to be re- 

 corded ; and the following particulars will, at least, serve to point out the way 

 for similar observations to be made in other eclipses, where different circum- 

 stances may chance to afford an opportunity lor gathering some addition to our 

 knowledge, with regard to the nature and condition of the moon, or of the sun, 

 and perhaps of both these heavenly bodies. 



Sept. 5, 1793, 8*' 40"' 3' by the clock * ; my attention being directed to the 

 place where I supposed the first impression would be made, I perceived two 

 mountains of the moon enter the disc of the sun, as delineated at a, b, fig. 7, 

 pi. 4. The time of their beginning to appear, when I saw them first, might be 

 I or 2 seconds past. — At 9'' 5'", 7-feet reflector ; power 287 ; the internal lu- 

 minous angle made on the sun, by the intersection of the limb of the moon, 

 which is now but little inore than a rectangle, is perfectly sharp up to the very 

 point. It is not in the least disfigured by the refraction of the lunar atmosphere. 

 The present shape of the angle however is not favourable for showing the effects 

 of that atmosphere. — At Q^ 17"", the luminous angles of the sun's preceding and 

 following limbs, which are now acute, remain perfectly sharp. One of them 

 indeed was disfigured, a little while before, by the entrance of a mountain of the 

 moon, but is now restored to its sharpness. — At 10'^ 5"" I delineated the appear- 

 ance of the limb of the moon on the sun, and found its mountains as in fig. 8. 

 At a, was a large table mountain, as it may be called, from its flat appearance ; 

 at b and c were elevated pointed rocks. Their appearance changing pretty fast, 

 no great accuracy can be expected in their expressed relative situation. 



I suppose the height of the most elevated of these mountains not to exceed a 

 mile and a half; for, on drawing several of them on the segment of a large cir- 

 cle, so as to look like what they appeared when projected on the sun, I found 

 them to be from the 1500th to the 2000th part of the diameter of that circle. 

 Then, putting the moon's diameter, as M. de la Lande states it, at 782 French 

 leagues, or 2151 English miles, we And the 1500th part of this to be less 

 than 1 mile and a half for the highest ; and the 2000th part, not quite 1 mile 

 and a 10th for the lowest. 



I attended all this time to the appearance of the sharp limb abc of the sun, 

 fig. 9, and suspected sometimes a little bending of the cusps outwards, as ex- 

 pressed at b in fig. 10 ; but, on long and attentive inspection, I could not 

 satisfy myself oi' its reality. If there was a bending, it did probably not amount 

 to 1 second of a degree; for, having formerly been much in the habit of mea- 

 suring the moon's mountains,-}- the quantity of 1", on its disc, was still familiar 



* By account, my sidereal time-piece was about 6" V.7 too forward ; but, as 110 transits had been 

 lately taken, there may be an error of some seconds. 



+ In the years 1771), 17 80, and 1781, I did not measure, I suppose, less llian an hundred moun- 

 tains of the moon, in whicli 1 used 3 dilieient methods : the projection of the tops of tliese inoun- 



