The Seventeenth Century 139 



Latin by Samuel Clark in 1697 (later editions in 1701 and 1718) 

 and into English by John Clarke D. D,, Dean of Sarum, in 1723. 

 Rohault discussed the question of light and colors in Part I, Chapter 

 27. He stated in his preface that he would follow Aristotle when he 

 fully agreed with him but not otherwise, warned against a too 

 experimental or too theoretical approach, and deplored the fact 

 that mathematics was not used more frequently by physicists. John 

 Clarke sought to modernize the work, for his translation carries 

 the title, Rohault's System of Natural Philosophy illustrated with 

 Dr. Samuel Clarke's Notes taken mostly out of Sir Isaac Newton's 

 Philosophy. The copious footnotes bring the treatise up to date, 

 but Rohault's ideas are left intact. 



Like Descartes, Rohault held " That there is such a Thing as 

 subtile Matter which penetrates the Pores of transparent Bodies." 

 Then he proceeded (Sec. 19) to " examine all the luminous bodies 

 that we know " and to show that they 



do actually push this Matter every Way; which they will be found to do 

 if it be true that the Parts are very small and very much agitated. . , . 

 And to begin with Flame. It has been already so plainly demonstrated 

 that it [flame] is composed of Parts very small, and which move with 

 the greatest Celerity, that it is superfluous to say any more about it. 



Rohault then proceeded to bring all other light sources in line 

 with the Cartesian view. He wrote (Sec. 20-26) : 



We see also, that there arises very bright Sparks upon striking a Flint 

 against Steel, or two Flints against each other, or an Indian Cane, against 

 a commoyi one, or by stroking the Back of a Cat in the Dark, when the 

 Weather is dry and cold, and in a Multitude of other Things. The 

 Cause of all which, is only this, that some of the Particles of these Bodies 

 being entangled between others, when they are struck, acquire in flying 

 off, a Motion like that of Flame, by which they in like manner push 

 forward the small Globules of the second Element.^^ 



There is some sort of rotten Wood, and of Fishes, when they begin 

 to be corrupted, which shine very bright. Now a Body cannot putrify 

 or be corrupted, but by the Motion of its Parts, some of which fly off 

 (as is evident in rotten Wood, from the Largeness of its Pores, and from 

 its Lightness, which render it different from what it was before; as a 

 Coal, and the Wood out of which it is made differ from each other.) 



^^ According to Descartes, light consisted of particles of the first element (materia 

 subtilis or coelestis) invading all space, even solid bodies. The push or pressure of 

 one particle on another was transmitted instantaneously as light from the sun through- 

 out the universe. The second element was made up of globules of matter between 

 stars and earth, and the globuli of the third element formed terrestrial bodies. Every 

 natural phenomenon was the result of conduction of motion from one element to 

 another, and every kind of material was determined by the relative amount and 

 motion of the three elements. 



