180 HOOKE'S VIBRATORY THEORY. 



"About eight years since, upon casually reading the 

 explication of this odd Phenomenon, by the most ingenious 

 Des Cartes, I had a great desire to be satisfied what that 

 Substance was that gave such a shining and bright light ; 

 and to that end I spread a sheet of white paper, and on it, 

 observing the place where several of these sparks seemed to 

 vanish, I found certain very small, black, but glistening 

 spots of a movable substance, each of which, examining 

 with my Microscope, I found to be a small, round Globule, 

 some of which, as they looked pretty small, so did they 

 from their surface yield a very bright and strong reflection 

 on that side which was next the Light, and each looked 

 almost like a pretty bright iron ball, whose Surface was 

 pretty regular. In this I could perceive the Image of the 

 Window pretty well, or of a Stick which I moved up and 

 down between the Light and it. Others I found which 

 were, as to the bulk of the ball, pretty regularly round, but 

 the Surface of them, as it was not very smooth, but rough, 

 and more irregular, so was the reflection from it more faint 

 and confused." {lb. p. 45.) " He that shall diligently 

 examine the Phaznomena of this Experiment will, I doubt 

 not, find cause to believe, that the reason I have heretofore 

 given of it is the true and genuine cause of it, namely, 

 That the Spark appearing so bright in the falling, is 

 nothing else but a small piece of the Steel or Flint, but most 

 commonly of the Steel, which, by the violence of the Stroke, 

 is, at the same time, severed and beatt red hot, and that 

 sometimes to such a degree as to make it melt together 

 into a small Globule of Steel ; and sometimes also is 

 that heat so very intense, as further to melt it and vitrifie 

 it ; but many times the heat is so gentle as to be able to make 

 the sliver only red hot, which, notzvithstanding falling upon 



