me 
24 On the Halo seen around all Bodies. 
constant motion. ‘That the conjunctival fluid is pushed together 
so as to form a ridge, can be proved by looking at the clear sky, 
or a candle, through a small pin-hole inaeard. On closing the 
lids slowly and then suddenly opening them, this ridge will be 
seen on the enlarged diameter of the pin-hole. 
10. I have stated in section 4th, that the halo is always of the 
same density and diameter at a cortaie point of view, and that on 
opening the closed eye it will suddenly contract, and that the — 
light diverging from it, will be much brighter. This contraction _ 
and expansion is not confined to those halos which adhere to. 4 
edges, or to a plane surface, for all narrow slits, all small circular — 
holes, contract and expand under similar circumstances. 
11. Light falls on the halo precisely as it does on a bright a 
brass ball. It is well known that if we breathe on the ball and _ 
pass the hand over it horizontally, the light from a self-luminous 
body will fall on it vertically. If the hand is passed over it ver- — 
tically, the light will fall horizontally. This phenomenon does — 
not arise from the presence of moisture, for the same thing occurs 
whether we breathe on the ball or not, although then not so per- 
ceptible. There are always inequalities even on the smoothest sur= 
face on which light would glance, but the peculiar feature of a — 
beam of light is more clearly defined when the hand is passed — 
over a moist surface; the ridges are then formed more distinctly. 
12. The cause of the formation of the ridges must be very _ 
obvious ; the hand i in passing across the ball, cannot come in con- 
tact with every part of the surface ; a number of elevations or 
ridges therefore will arise parallel to the motion of the hand, and 
it is across these ridges, at right angles, that light falls. 
13. But on account of the sphericity of the ball, the beam of — 
light will be of very narrow diameter, as it can only glance over 
a very circumscribed area, which area, however, is the prominetify = 
point of the ball. ie | 
14. The halo siocdinpnnine every one of the ridges following ‘ 
these elevations and depressions. It is always parallel to every 
plane or curved surface and edge, and the lines intersect each — 
other at every angular point and anand every curve or sphere 
without interfering. 
‘ 15. If it be a plane surface on which we breathe, and seed 
hand i 
is passed over it vertically, the light will glance across the 
whole mass of ridges in a horizontal direction. A contrary ac- 
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