901 



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, deflected, 

 inflected by bodies near which they pass. 



Proposition I. 



The flexion of any pencil or beam, w hether of white or of homo- 

 geneous 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, con- 

 tinually decreasing as they recede from the bending body, in de- 

 flexion, where only one bending body is acting ; and they are real 

 images of the luminous body by whose light they are formed. 



Proposition II. 



The rays of light when inflected by bodies near which they pass 

 are thrown into a condition or state which disposes them to be on 

 one side more easily deflected than they w^re before the first flexion ; 

 and disposes them on the other side to be less easily deflected : and 

 when deflected by bodies they are thrown into a condition or state 

 which disposes them to be more easily inflected, and on the other 

 side to be less easily inflected than they were before the first flexion. 



Proposition III. 



The disposition communicated to the rays by the flexion is alter- 

 native ; and after inflexion they cannot be again inflected on either 

 side ; nor after deflexion can they be deflected. But they may be 

 deflected after inflexion, and infl.ected after deflexion, by acting on 

 the sides disposed, and not by acting upon the sides polarized. 



Proposition IV. 



The disposition impressed upon the rays, whether to be easily de- 

 flected or easily inflected, is strongest nearest the first bending body, 

 and decreases as the distance increases. 



Proposition V. 



The fringes made by the second body acting upon the rays de- 

 flected by the first, must, according to the calculus applied to the 

 case, be broader than those made by the second body deflecting those 

 rays inflected by the first. 



Proposition VI. 



When one body only acts upon the rays, it must, by deflexion, form 

 them into fringes or images decreasing as the distance from the 

 bending body increases. But when the rays deflected and disposed 

 by one body are afterwards inflected by a second body, the fringes 

 will increase as they recede from the direct rays. Also when the 

 fringes made by the inflexion of one body, and which increase with 

 the distance from the direct rays, are deflected by a second body. 



