on the Affections and Properties of Light, 3 69 
Distance of the speculum from the hole in the 
Inches. 
Parts. 
window-shut - 
24. 
Distance of the speculum from the stage of the 
micrometer - 
l8. 
Transverse axis of the sun’s image 
2. 
6 
Conjugate axis of the sun’s image 
1 . 
4 
Length of the oblong dark spot 
.4 
Breadth of the oblong dark spot 
- 
.0074 
Breadth of its first fringe 
- 
,0022 
Elliptic spot’s transverse axis 
.0116 
conjugate axis 
- 
.0068 
Breadth of its first fringe 
- 
.0034 
Transverse axis of a larger elliptic spot 
.013 
Conjugate axis of the same spot 
-- 
.0076- 
In the image where these measures were taken, there were 
seven other elliptic spots, a little less and nearly equal; all the 
others were much smaller and more confused. 
Observation 6. On viewing the surface of the speculum at- 
tentively in that place whence the rays formed the oblong and 
first mentioned elliptic spots, I saw a dark but very thin long 
scratch, and a dark dent, similar in shape to the dark spaces 
on the image; the dark spot measured less than of an inch; 
which makes its whole surface to the whole polished surface 
as 1 to 34225, supposing the former circular or nearly so. All 
these measures will be found to agree very well, for their small- 
ness and delicacy : thus, the ratio last mentioned is nearly the 
same which we obtain by comparing the image and the spot ; 
the like may be said of the two spots mentioned in the table. 
