VOL. VIII.] PHILOSOPHICAL TRANSACTIONS. SQ 



medium. This appears by several passages in the Transactions p. 23, 24, 25, 

 26, and 27, and is capable of farther proof. 



7. The rays of light suffer not any change of their qualities from refraction. 



8. Nor afterwards from the adjacent quiet medium. These two propositions 

 are manifest de facto in homogeneal light, whose colour and refrangibility is not 

 at all changeable, either by refraction or by the contcrmination of a quiet me- 

 dium. And as for heterogeneal light, it is but an aggregate of several sorts of 

 homogeneal light, no one sort of which suffers any more alteration than if it 

 were alone, because the rays act not on one another by prop. 6. And there- 

 fore the aggregate can suffer none. These two propositions also might be fur- 

 ther proved apart by experiments, too long to be here described. 



9. There can no homogeneal colours be educed out of light by refraction, 

 which were not commixed in it before: because, by prop. 7 and 8, refraction 

 changes not the qualities of the rays, but only separates those which have divers 

 qualities, by means of their different refrangibility. 



10. The sun's light is an aggregate of an indefinite variety of homogeneal 

 colours; by prop. 1, 3, and 9. And hence it is that I call homogeneal colours 

 also primitive, or original. And thus much concerning colours. 



Mons. N. has thought fit to insinuate, that the aberration of rays, by their 

 different refrangibility, is not so considerable a disadvantage in glasses as I seem- 

 ed to be willing to make men believe, when I propounded concave mirrors as 

 the only hopes of perfecting telescopes. But if he please to take his pen, and 

 compute the errors of a glass and speculum that collect rays at equal distances, 

 he will find how much he is mistaken, and that I have not been extravagant, as 

 he imagines, in preferring reflexions. And as for what he says of the difficulty 

 of the praxis, I know it is very difficult, and by those ways which he attempted 

 it I believe it impracticable. But there is a way insinuated in the Transactions, 

 by which it is not improbable but that as much may be done in large 

 telescopes, as I have thereby done in short ones, but yet not without more than 

 ordinary diligence and curiosity. 



Strange Effect of Thunder and Lightning, on Wheat and Rye in the Granaries of 

 Dantzick. By M. Christ. Kirhhy. N° 96, p. 6092. 

 You doubtless know how much this city is famed for its numerous and conve- 

 nient granaries, it being the repository of all sorts of grain the fruitful kingdom 

 of Poland affords. In those granaries are laid up chiefly wheat and rye, in par- 

 cels of 20 to 30 and 60 lasts in one chamber, according to its size, and the dry- 

 ness of the corn ; which they turn over 3, 4, 5, 6 times a week, as need requires, 

 to keep it svveet and fit for shipping. Now it happened, that about the latter 



VOL. II, N 



