742 PHILOSOPHICAL TBANSACTIONS. [aNNO 17 q6. 



bent into dg ; but because of the different inflexibility of its parts, the red will 

 be bent into dr, and the violet into dv, and the intermediate rays will fall be- 

 tween R and V, the whole forming an image rgv, separated into the 7 primary 

 colours; and in like manner, by the different deflexibility of the parts whereof 

 s'd' consists, an image without the shadow, as v'gV will be formed, similar to 

 VGK, r' being red and v' violet ; all which is both theory and experience ; and 

 the same explanation may be extended to the other cases. Now, in all these, 

 the bending power stretching to a very small definite distance, and being of dif- 

 ferent degrees of strength at different distances from the body, several pencils or 

 small beams, passing through different parts of the spheres, will be acted on by 

 the power in its different states of strength ; and each beam will be disposed into 

 an image in the way before described ; of these images I have sometimes observed 

 4, and even, by using great care, the faint lineaments of a 5th. In forming 

 them, the power acts strongest at the smallest distances, and of consequence 

 bends the mean flexible rays, that pass near, farther inwards or outwards than 

 those that pass farther ott'; so that the extreme rays will in the former case be 

 more separated from the mean than in the latter ; and the nearer image will al- 

 ways be the largest and most highly coloured ; which is consistent with fact. 

 This explains fully the celebrated experiment of Sir Isaac Newton, with the 

 knives, and the explanation is confirmed by the experiments related above on 

 flexibility, where the bending force acted most strongly on those images formed 

 out of red light, and least strongly on those formed out of violet and blue light. 

 Other phenomena are explicable on the same principles, being only particular 

 cases as it were of the coloured fringes or images. I shall mention a few of the 

 most remarkable. 



6. When making some of the experiments related in the course of this 

 paper, I observed that when the sun was surrounded, but not covered, by clear 

 white clouds, the white image on the chart (the hole being li- inch in diameter) 

 was surrounded by 2 rainbows, pretty broad and bright: in the colours were red 

 on the outside, and violet next the white of the image. These bows must not 

 be confounded with one which sometimes appears wholly of a dull red and 

 yellow, when the sun or moon shines through a cloud, and which is owing to 

 the direct transmission of the red rays and reflection of the others; for not only 

 are the colours difterent in species, in brightness, and in number, in the phe- 

 nomena under discussion, but also they are formed by the hole in the window, 

 as I knew by altering its shape into an oblong; and the colours now were not 

 disposed in circles, but in broad lines of the san)e breadth, as the bows had 

 been, running along the shadow of the hole's sides, and in the same position 

 of colours as before. It is evident that their cause is the inflection of the light 

 which comes from the clouds by the sides of the hole (for if the sky have no 

 clouds the colours do not appear.) which separate the white light into the parts 

 of which it is composed. 



7. It is observable, that when we look at any luminous body, at a distance 



