150 Dr. Herschell’s Experiments for Investigating 
applicable to such as have in the first been made by convex 
glasses. 
That the colours in all prismatic phenomena, which have 
been examined in the 44th, 45th, 46th, 47th, and 48 articles of 
my paper, are produced either by the interior critical separa- 
tion arising from the different reflexibility of the rays which 
cause the blue bow, or by the exterior critical separation 
arising from the different intromissibility of the rays which 
cause the red bow, has been so clearly and circumstantially 
proved that it can admit of no doubt ; it may even be con- 
ceived by some that I have been too particular in giving the 
precise angles, when zve see in the Lectiones Opticce , Sect. II. 
Par. 2, page 257, 258, how far Sir I. Newton has explained the 
blue bow ; but a sufficient reason for this minuteness was to 
give greater clearness to my explanation of the new pheno- 
menon of a red bow, which I have with equal precision de- 
scribed, and which by this means may be, step by step, 
compared with the production of the blue bow. By this pre- 
caution I hoped to anticipate any objection that might occur, 
such as, for instance, that Sir I. Newton has also explained the 
red bow which (it may be supposed) is merely the converse of the 
blue bozv. This conception, although Newton no where speaks 
of a red bow, seems to be countenanced by what is said after 
he has shown that the blue bow is caused by the different re- 
flexibility of the rays of light ; for as he affirms that the red, 
orange, and yellow colours are transmitted, he contrives a 
method of proving it experimentally, by adding a second 
prism, placed under that which gives the blue bow, and thus 
making the transmitted rays visible. The full import of this 
