OX LIGHT AXD COLOURS. 



123 



have generally been obliged to encounter the inconvenience 

 of the motion of the sun's image, especially when I had to 

 work with small pencils of light. This inconvenience is 

 materially lessened by using horizontal prisms and plates. 



Although I have made mention of the apparatus of great 

 delicacy which I employed, it must be observed that this is 

 only required for experiments of a kind to depend upon nice 

 measurements. All the principles which I have to state as 

 the result of my experiments in this paper, can be made with 

 the most simple apparatus, and without any difficulty or 

 expense, as will presently appear. 



It is perhaps unnecessary to make an apology for the form 

 of definitions and propositions into which my statement is 

 thrown. This is adopted for the purpose of making the 

 narrative shorter and more distinct, and of subjecting my 

 doctrines to a fuller scrutiny. I must further premise that I 

 purposely avoid all arguments and suggestions upon the two 

 rival theories the Newtonian or Atomic, and the Undulatory. 

 The conclusions at which I have arrived are wholly inde- 

 pendent, as it appears to me, of that controversy. I cau- 

 tiously avoid giving any opinion upon 4t ; 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 " Eieniste," and neither 

 " ondulationiste " nor " anti-ondulationiste." 



Chateau Eleanor-Louise (Provence^),* 

 1st 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 flection is the better word. 



* 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. 



