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EXPERIMENTS AND INVESTIGATIONS 



2. Flexion is of two kinds inflexion, or the bending towards 

 the body ; deflexion, or the bending from the body. 



3. Flexibility, deflexibility , inflexibility, express the disposition 

 of the homogeneous or colour-making rays to be bent, de- 

 flected, inflected by bodies near which thev pass. 



Although there is always presumed to be a flexion and a 

 separation of the most flexible rays from the least flexible 

 (the red from the violet for example) when they pass by 

 bodies, yet the compound rays are not so presumed to be 

 decomposed when reflected by bodies. This is probably 

 owing to the successive inflexions and deflexions before and 

 after reflexion, correcting each other and making the whole 

 beam continue parallel and undecomposed instead of be- 

 coming divergent and being decomposed. 



PROPOSITION I. 



The flexion of any pencil or beam, whether of white or of 

 homogeneous light, is in some constant proportion to the 

 breadth of the coloured fringes formed by the rays after 

 passing by the bending body. Those fringes are not three, 

 but a very great number, continually decreasing as they 

 recede from the bending body, in deflexion, where only one 

 body is acting ; and they are real images of the luminous 

 body by whose light they are formed. 



Exp. 1. If an edge be placed in a beam or in a pencil of 

 white light, fringes are formed outside the shadow of the 

 edge and parallel to it, by deflexion. They are seen distinctly 

 to be coloured, the red being furthest from the shadow, the 

 violet nearest, the green in the middle between the red and 

 the violet. The best way to observe 

 this is to receive the light on an instru- 

 ment composed of two vertical and two 

 horizontal plates, each moving by a 

 screw so as to increase or lessen the 

 distance between the opposite edges. 

 a, a' are (fig. 1) the vertical, b, b' the 

 horizontal edges, s, s are the screws ; and these may be fitted 



