734 PHILOSOPHICAL TEANSACTIONS. [aNNO I672. 



ways of making experiments of refraction, prescribed by Vitello, Descartes, 

 Riccioli and Manzini. And then describes an instrument of his own invention 

 for that purpose, &c. 



The third letter is concerning a book of Dr. Mengoli ; wherein is a table of 

 refractions for every degree of altitude. But Cassini shows that table of Men- 

 goli to be false ; as being easily refuted by experience, and grounded upon a 

 wrong foundation. 



IV. Dr. Richard Sharrock's History of the Propagation and Improvement of 

 Vegetables, &c. the 2d ed. Oxford, 1672, in 8vo. 



This treatise shows the several ways for the propagation of plants usually 

 cultivated in England, as they are increased by seed, offsets, suckers, truncheons, 

 cuttings, slips, laying, circumposition : the several ways of graftings and ino- 

 culations ; as likewise the methods for the improvement and culture of field,^ 

 orchard and garden plants, &c. 



A Series of Quceries proposed hy Mr. Isaac Newton, to he determined 

 by Experiments, positively and directly co7icluding his new Theory of 

 Light and Colours, imparted to the Editor in a Letter of the said 

 Mr. Newton's, of July 8, 1672. iV"85, p. 5004. 



Give me leave. Sir, to insinuate that I cannot think it effectual for determin- 

 ing truth, to examine the several ways by which phasnomena may be explained, 

 unless where there can be a perfect enumeration of all those ways. You know 

 that the proper method for inquiring after the properties of things, is to deduce 

 them from experiments. And I told you that the theory which I proposed was 

 evinced to me, not by inferring it is thus because not otherwise, that is, not by 

 deducing it only from a confutation of contrary suppositions, but by deriving 

 it from experiments concluding positively and directly. The way therefore to 

 examine it is by considering, whether the experiments which I proposed do 

 prove those parts of the theory to which they are applied ; or by prosecuting 

 other experiments which the theory may suggest for its examination. And this 

 I would have done in a due method ; the laws of refraction being thoroughly in- 

 quired into and determined before the nature of colours be taken into con- 

 sideration. It may not be amiss to proceed according to the series of these 

 quaeries; which I could wish were determined by the event of proper experi- 

 ments ; declared by those that may have the curiosity to examine them. 



1 . Whether rays, that are alike incident on the same medium, have unequal 

 refractions ; and how great are the inequalities of their refractions at any in* 

 cidence ? 



