A reply to Mr. Robin's remarks on the Essay upon distinct and indistinct vision published at the end of Dr. Smith's Complete system of optiks / by James Jurin.
- James Jurin
- Date:
- 1739
Licence: Public Domain Mark
Credit: A reply to Mr. Robin's remarks on the Essay upon distinct and indistinct vision published at the end of Dr. Smith's Complete system of optiks / by James Jurin. Source: Wellcome Collection.
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![[ 3 ] light is uniformly fpread thro9 his circles of difipati- on ; whereas he confeffes at art. 220. that the den- fity of the light is different in different parts of thefe circles. Now, as I apprehend, in writing upon an intricate fubjedt, the way to be underftood is to put the Ampler cafes firft, and afterwards to pro¬ ceed to the more compound. Accordingly, I treated of the light as uniformly fpread, fo long as the appearances I was explaining, did not re¬ quire its inequality to be confidered. And be¬ fore I entred upon thole cafes, where it was ne- ceflary to confider that inequality, l did in art. 197. exprefs myfelf in the following manner. 46 This circle (of diffipation) we have hither- €4 to treated of, asuf it were uniformly lumi- 44 nous, or as if the rays of the pencil were 44 equally and uniformly fpread over the whole 44 circle. But in reality the fadt is otherwife: 44 the rays are not evenly difpofed all over this €C circle, but are denfer in fome parts of it than 44 in others. And though in many cafes, and 44 indeed in moft of the phenomena above re- *4 lated, this inequality of the denfity of the 44 rays is not very confiderable, nor occafmns 44 any great change in the appearance, yet there 44 are fome few of them that will be remarkably 44 affedted by it; and there are fome other very 44 uncommon and furprifing appearances, that 44 are not to be accounted for from the common 44 laws of Opticks, and depend wholly upon 44 this inequality of the rays in different parts 44 of the circle of diffipation.35 This pafiage in art. 197. which fo plainly and fully exprefies the reafon of my proceeding, as well as the two hints I had before given in art 66](https://iiif.wellcomecollection.org/image/b30780287_0011.jp2/full/800%2C/0/default.jpg)
