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A POPULAR ACCOUNT 



sics, which cannot properly find a place 

 here. To this, however, we must make 

 exception of that (the 26th) in which 

 he points out the polarity of light, to 

 the merit of having first suggested which 

 he has an undoubted right. " If the 

 planes of perpendicular refraction of one 

 piece of Iceland spar be at right angles 

 with those of another, the rays which 

 are refracted after the usual manner by 

 the first crystal will be all refracted 

 after the unusual manner in passing 

 through the second crystal ; and the rays 

 which are refracted after the unusual 

 manner in passing through the first 

 crystal will be all of them refracted 

 after the usual manner in passing 

 through the second." Hence Newton 

 concluded, that the rays have sides, pos- 

 sessing different properties, in virtue of 

 which they will be differently refracted, 

 according to the direction in which the 

 crystal is presented to them. If the 

 ray be successively transmitted through 

 two crystals, and is placed in the same 

 manner with respect to the planes of 

 both, it will be refracted in the same 

 manner by both ; but if that side of 

 the ray which looks towards the coast 

 of unusual refraction in the first crys- 

 tal be at right angles with that side 

 of the same ray which looks towards 

 the coast of unusual refraction in the 

 second crystal, the ray shall be re- 

 fracted after several manners in seve- 

 ral crystals. There is nothing more 

 required to determine whether the rays 

 of light, which fall upon the second crys- 

 tal, shall be refracted after the usual or 

 after the unusual manner, but to turn 

 about this crystal, so that the coast of 

 its unusual refraction may be on this 

 or on that side of the ray. And there- 

 fore every ray may be considered as 

 having four sides or quarters, two of 

 which opposite to one another incline the 

 ray to be refracted after the unusual man- 

 ner, as often as either of them are turned 

 towards the coast of unusual refraction, 

 and the other two, whenever either of 

 them are turned towards the coast of 

 unusual refraction, do not incline it to 

 be otherwise refracted than after the 

 usual manner. The first two may 

 therefore be called the sides of unusual 

 refraction. 



We cannot better conclude the rapid 

 sketch which we have attempted to give of 

 this extraordinary production of human 

 genius, than by quoting some precepts 

 which have been most admirably illus- 

 trated in the works of this illustrious 

 philosopher. "The main business of 



natural philosophy is to argue from phe- 

 nomena without feigning hypotheses, and 

 to deduce causes from effects until we 

 come to the very First Cause, which cer- 

 tainly is not mechanical ; and not only 

 to unfold the mechanism of the world, 

 but chiefly to resolve these and such 

 like questions : What is there in places 

 almost empty of matter, and whence is 

 it that the sun and planets gravitate to- 

 wards one another without dense mat- 

 ter between them ? Whence is it that 

 nature doth nothing in vain ? and whence 

 arise all that order and beauty which 

 we see in the world ? To what end are 

 comets, and whence is it that planets 

 move all in one and the same way 

 in orbits concentric, while comets 

 move in all manner of ways, in orbits 

 excentric ; and what hinders the fixed 

 stars from falling on one another? How 

 came the bodies of animals to be con- 

 trived with so much art, and for what 

 ends were their several parts ? Was the 

 eye contrived without skill in optics, and 

 the ear without knowledge of sounds ? 

 How do the motions of the body fol- 

 low from the will, and whence is the in- 

 stinct of animals ? Is not the sensory of 

 animals that place to which the sensitive 

 substance is present, and into which the 

 sensitive species of things are carried 

 through the nerves and the brain, that 

 there they may be perceived by their 

 immediate presence to that substance ? 

 And these things being rightly dis- 

 patched, does it not appear from phe- 

 nomena.that there is a Being incorporeal, 

 living, intelligent, omnipresent, who, in 

 infinite space, as it were in his sensory, 

 sees the things themselves, intimately 

 and thoroughly perceives them, and 

 comprehends them wholly by their im- 

 mediate presence to himself; of which 

 things the images only, carried through 

 the organs of sense into our little sen- 

 soriums, are there seen and beheld by 

 that which in us perceives and thinks. 

 And though every step in this philoso- 

 phy brings us not immediately to the 

 knowledge of the First Cause, yet it 

 brings us nearer to it, and on that ac- 

 count is highly to be valued. * * * * 

 And if natural philosophy in all its parts 

 shall at length be perfected, the bounds 

 of moral philosophy shall also be en- 

 larged. For so far as we can know by 

 natural philosophy what is the First 

 Cause, what power he has over us and 

 what benefits we receive from him, so 

 far our duty towards him as well as that 

 towards one another, will appear to us 

 by the light of nature." 



