236 
LORD BROUGHAM’S EXPERIMENTS AND OBSERVATIONS 
suggestions upon the two rival theories — the Newtonian or Atomic, and the Undula- 
tory. The conclusions at which I have arrived are wholly independent, as it appears 
to me, of that controversy. I cautiously avoid giving any opinion upon it ; and 
instead of belonging to the sect of undulationists or anti-undulationists, I incline to 
agree with my learned and eminent colleague M. Biot, who considers himself as a 
“ Rieniste,'' and neither “ ondulationiste ” nor “ anti-ondulationiste.” 
Chateau Eleanor- Louise [Provence)*, 
November 1849. 
Definitions. 
1. Flexion is the bending of the rays of light out of their course in passing near 
bodies. This has been sometimes termed diffraction, but Jiexion is the better word. 
2. Flexion is of two kinds — inflexion, or the bending towards the body ; deflexion, 
or the bending from the body. 
3. Flexibility , de flexibility , inflexibility, express the disposition of the homogeneous 
or colour-making rays to be bent, deflected, inflected by bodies near which they 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 de- 
flexions before and after reflexion, correcting each other and making the whole beam 
continue parallel and undecomposed instead of becoming divergent and being de- 
composed. 
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 instrument composed of two vertical and 
two horizontal plates, each moving by a screw so as to increase or lessen the distance 
* In experiments at this place, in winter, I found one great advantage, namely, the more horizontal direction 
of the rays. In summer they are so nearly vertical, that a mirror must be used to obtain a long beam or pencil, 
which is often required in these experiments, and so the loss of light countervails the greater strength of the 
summer sun’s light. 
