S 1 3 
chiefly on the Reflexibility of Light. 
Newton fit tomber un rayon blanc perpendiculairement a 
la face anterieure d’un prisme: puis, tournant le prisme sur 
son axe, il observoit la reflexion qui s’opbroit a sa face poste- 
rieure. II vit le violet se reflechir le premier; puis les autres 
rayons, dans 1’ordre de leurs refrangibilitbs, jusqu’au rouge, 
qui fut reflechi le dernier. II en conclut, que le violet est re- 
flechi sous un moindre angle d’incidence que le rouge. (Ex- 
pbr. g.) 
(Test cette conclusion que M. Brougham attaque ; et, pour 
ne point altbrer sa pensbe, je vais transcrire ici ses expressions. 
“ That the demonstration involves a logical error, appears 
“ pretty evident. When the rays, by refraction through the 
“ base of the prism used in the experiment, are separated into 
“ their parts, these become divergent, the violet and red emer- 
“ ging at very different angles, and these were also incident on 
“ the base at different angles, from the refraction of the side 
“ at which they entered ; when, therefore, the prism is moved 
“ round on its axis, as described in the proposition, the base is 
“ nearest the violet, from the position of the rays by refraction, 
“ and meets it first ; so that the violet being reflected as soon 
“ as it meets the base, it is reflected before any of the other 
“ ra}^s, not from a different disposition to be so, but merely 
from its different refrangibility.” 
Ainsi M. Brougham pense que la reflexion du rayon violet 
ne precede celle du rayon rouge, que parceque la refraction 
qui a lieu a la surface antbrieure, force le rayon violet a at- 
teindre la surface posterieure plutdt que ne peut le faire le 
rouge. 
- Mais il semble que l’effet est ici en sens inverse de la cause. 
Ecartons d’abord un faux sens. Il est impossible que hauteur 
mdccxcviii. S s 
