the Inflection , Reflection, and Colours of Light. 267 
at a still less distance, it again becomes repulsive ; and at the 
least distance, it becomes attractive as before ; always acting 
in the same direction. These things hold whatever be the 
direction of the particles ; but if, when produced, it passes 
through the body, then the nearest repulsive force drives the 
particles back, and the nearest attractive force either transmits 
them, or turns them out of their course during transmission. 
Farther, the particles differ in their dispositions to be acted 
upon by this power, in all these varieties of exertion ; and 
those which are most strongly affected by its exertion in one 
case, are also most strongly affected by that exertion when 
varied; except in the cases of refraction, of which we before 
spoke ; and these dispositions of the parts are in all the cases in 
the same harmonical ratio. Lastly, the cause of these different 
dispositions is the magnitude of the particles being various. 
All that remains now to be done on this part of the subject 
is to explain one or two phcenomena relating to reflexibility. 
1. It has been remarked, that if we look at a candle, or 
other luminous body, with our eyes almost shut, bright streaks 
seem to dart upwards and downwards from it. Newton* ex- 
plains this by refraction through the humours adhering to the 
eyelids. RoHAULT-f and Mr. Young J ascribe them to re- 
flections. Des Cartes makes them arise from wrinkles on 
the eye's surface. De la Hire from refraction through the 
moisture on the eyelids, as through a concave lens ; and 
Priestley || from inflection through the lashes. The truth 
of Sir Isaac's explanation is obvious, because the streaks 
which dart from the top of the luminous body are formed 
* Lect. Opt. Sed. III. adfinem. f Physica, p.249. Clark’s ed. 
t Phil. Trans. 1793. || On Vision, Vol. II. 
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