Telescope, &c. were first knoivn in England, 73 



cally as' the distance of the image too; and, lastly, the 

 false conclusions he has drawn, and must always draw, from 

 these principles ; as I (says the doctor) have shown in his 

 attempt upon making spectacles. " The theory of vision is 

 very difficult. I believe it now exercises the genius of those 

 excellent philosophers and mathematicians Dr. Young, and 

 your correspondent Dr. Wollaston, and therefore cannot, 

 even at this hour, be considered as completely unfolded 

 and established in all its parts. With respect to " the false 

 principle Bacon maintains, that the apparent magnitude ot* 

 an object," &x. it is observable that, when the angles are 

 small, the two ratios he gives are nearly equal, and there- 

 fore that the ratio compounded of both is nearly the dupli- 

 cate of either. Not having the Opus Majus, I cannot say 

 whether Bacon means the apparent magnitude of the sur- 

 face of an object, or of its height or breadth only. But 

 whether he mean the one or the other, and whether the/, 

 principle, as he applies it, be true or false, it seems rather 

 too much to expect from Bacon an accuracy which, in se- 

 veral instances, modern philosophers have yet to seek. For 

 example, it is not yet entirely settled, whether the forces 

 of bodies hi motion be as the masses and the velocities 

 simplv, or as the masses and the squares of the velocities. 

 And Dr. S. should have remembered that, in his 107th 

 remark, he had said that the (i great Descartes is quite 

 mistaken in his method of demonstrating the effects of 

 telescopes ;" that his demonstration " can never be made 

 sense of; and that, though many others have since been 

 labouring at the same problem, which is the chief of all, 

 yet none of them have been able to solve it." From these 

 failures, however, Dr. S. does not infer an utter ignorance 

 of the telescope. Why are different measures of cri- 

 ticism to be thus applied to Roger Bacon and to some of 

 the greatest of the moderns? Jt may be said, that it was 

 necessary for Dr. S. to expose his author's faults in order to 

 prove, that " he was not qualified to invent a telescope by 

 theory," this being the subject of this (118th) remark. 

 But where was the necessity of showing that Bacon was not 

 qualified to do that which, by the account of Huygens, 

 acquiesced in by Dr. S. (in his 103d remark) required 

 " abilities more than human ?" No one affirms that Bacon 

 had theory sufficient to conduct him to the invention of the 

 telescope. But had Porta, Jansen, Metius, Lippersheim, or 

 even Galileo, such a sufficiency of this refined theory ? Surely 

 Dr. S. would not have asserted this. Yet it is a fact that one 

 pr more of these men invented,, or rather re-invented, the 



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