ATTACKS UPON YOUNG. 345 



tion, the writer, the geometer, the experimenter, with a 

 vehemence, with a severity of expression almost with- 



experimental cases which he had examined. In all these there is no 

 unity or community of principle, there is at least nothing like the spirit 

 of theory, no continual recurrence to one leading idea, no perpetual 

 appeal to any one principle however imaginary, but an attempt in each 

 isolated case to frame something like an isolated hypothesis to suit it, 

 and in some way to represent its phenomena though without any 

 attempt to connect them with the others. It may perhaps be said that 

 all these various suppositions agree in supposing light to be material, 

 to be something emitted from the luminous source. But on a closer 

 examination it seems far from certain that even this can be main- 

 tained. The only part of these investigations, perhaps, in which any 

 thing very positive of this kind is distinctly introduced, is when New- 

 ton investigates the laws of refraction, on the express supposition of 

 smah 1 molecules attracted by the molecules of the medium. But in 

 this instance it has been truly observed, that at the time when New- 

 ton wrote, no mathematical method existed by which this kind of 

 action could be reduced to calculation except those involving the ac- 

 tion of attractive force. To give, then, a mathematical theory of ordi- 

 nary reflexion and refraction he was necessitated to make use of this 

 method. When he came to investigate those more recondite phenom- 

 ena which he (very appropriately to their apparent nature) called 

 "inflexion," the idea most naturally and obviously presented was, 

 that some power or influence, analogous to attraction and repulsion, 

 existing in the edge of an opaque body to bend out of their course rays 

 passing very near it, and this might seem to imply the materiality of 

 those rays. A kind of alternating action of this sort, which he imag- 

 ined necessary to account for a part of the effect, would, however, 

 hardly be reconcilable to the idea of direct emission. It would be a 

 difficult matter to conceive particles darted through space with such 

 inconceivable velocity as must belong to those of light, and yet stop- 

 ping to wave about, in and out, as Newton expresses it, " like an eel," 

 close to the edge of a body, by virtue of some mysterious influence 

 which it exercises upon them. 



Again: the theory of those alternating states, conditions, or "fits" 

 as he termed them, at such minute intervals along the length of ray 

 alternately putting it in a state to be reflected, and again to be trans- 

 mitted by a transparent medium, seem very remote from the idea of a 

 simple rectilinear progress of molecules through space following one 

 another at immense intervals of distance though in inconceivably rapid 



15* 



