11 
relative to physical Optics. 
“ show that this effect depends upon some property which the 
“ drops retain, whilst they are in the upper part of the air, but 
“ lose as they come lower, and are more mixed with one ano- 
“ ther.” Phil. Trans. Vol. XXXII. p. 243. 
From a consideration of the nature of the secondary rainbow, 
of 54°, it may be inferred, that if any such supernumerary colours 
were seen attending this rainbow, they would necessarily be 
external to it, instead of internal. The circles sometimes seen 
encompassing the observer’s shadow in a mist, are perhaps more 
nearly related to the common colours of thin plates as seen by 
reflection. 
IV. ARGUMENTATIVE INFERENCE RESPECTING THE NATURE OF 
LIGHT. 
The experiment of Grimaldi, on the crested fringes within 
the shadow, together with several others of his observations, 
equally important, has been left unnoticed by Newton. Those 
who are attached to the Newtonian theory of light, or to the 
hypotheses of modern opticians, founded on views still less en- 
larged, would do well to endeavour to imagine any thing like 
an explanation of these experiments, derived from their own 
doctrines; and, if they fail in the attempt, to refrain at least 
from idle declamation against a system which is founded on the 
accuracy of its application to all these facts, and to a thousand 
others of a similar nature. 
From the experiments and calculations which have been pre- 
mised, we may be allowed to infer, that homogeneous light, at 
certain equal distances in the direction of its motion, is possessed 
of opposite qualities, capable of neutralising or destroying each 
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