4 1 
late Eclipse of the Sun. 
I attended all this time to the appearance of the sharp limb 
a b c of the sun, fig. 3, and suspected, sometimes, a little 
bending of the cusps outwards, as expressed at b in fig. 4 ; 
but upon long, and attentive inspection, I could not satisfy my- 
self of its reality. If there was a bending, it did probably not 
amount to one second of a degree ; for, having formerly been 
much in the habit of measuring the moon's mountains,* the 
quantity of one second, on its disk, was still familiar enough 
to me to estimate it pretty exactly. 
io h 15'. I looked out with the natural eye for the planet 
Venus, and soon perceived her. In the telescope, with 287, 
she appeared very sharp and well defined, and was a little 
gibbous. 
It may seem, perhaps, extraordinary that in the trial above 
mentioned, the eye should be able to ascertain the proportion 
of a quantity so little as the fifteen hundredth, or two thou- 
sandth part of the diameter of the moon ; but the experiment 
may be easily repeated in the following manner : 
Upon a line, six or eight inches long, drawn on a sheet of 
paper, make several small marks, representing mountains on 
the projected circumference of a large globe. The paper be- 
ing then placed in a proper light and situation, withdraw the 
eye to the distance of 7, 8, or 9 feet, and take notice which of 
the marks appear of the same size, and distinctness, with the 
* In the years 1779, 1780, and 1781. I did not measure, I suppose, less than an 
hundred mountains of the moon, in which I used three different methods : the projec- 
tion of the tops of these mountains beyond the enlightened part of the disk ; the length 
of their shadow on the surface of the moon ; and their perpendicular projection on the 
full edge of the moon’s limb. Some of these observations are contained in a former 
paper (see Phil. Trans. Vol. LXX. Part II. page 507) ; but most of them remain 
uncalculated in my journal, till some proper opportunity. 
MDCCXCIV. G 
