g4 PHILOSOPHICAL TRANSACTIONS. [aNNO 1073. 



An Aiisiver to the former Letter, ivritten June 10, l673, hy the same Parisian 

 Philosopher, who wrote the Letter already extant in N° 96, p. 85, N° 97, 

 p. 6112. 



Touching the sokitions, given by M. Newton to the scruples by me proposed, 

 about his theory of colours, there were matter to answer them, and to form 

 new difficulties; but seeing that he maintains liis opinion with so much concern, 

 I list not to dispute. But what means it, I pray, that he says; though I should 

 show him, that the white could be produced of only two uncompounded colours, 

 yet I could conclude nothing from that. And yet he has affirmed in N° 80, of 

 the Transactions, that to compose the white, all primitive colours are necessary. 



As to the manner in which he reconciles the effect of convex glasses for so 

 well assembling the rays, with what he establishes concerning the different re- 

 frangibility, I am satisfied with it ; but then he is also to acknowledge, that this 

 aberration of the rays is not so disadvantageous to optic glasses, as he seems to 

 have been willing to make us believe, when he proposed concave speculums as 

 the only hopes of perfecting telescopes. His invention certainly was very good; 

 but, as far as I could perceive by experience, the defect of the matter renders it 

 as impossible to execute, as the difficulty of the form obstructs the use of the 

 hyperbola of M. Descartes : so that, in my opinion, we must stick to our 

 spheric glasses, which we are already so much obliged to, and that are yet 

 capable of greater perfection, as well by increasing the length of telescopes, as 

 by correcting the nature of glass itself. 



To this letter is to be referred that, which is already extant in N° 96, p. 86, 

 as being an answer thereto. 



On Ambergris. By Mr. Boyle. N° 97, p. 6ll3. 



On Ambergris.^ Extracted from a Dutch Journal, belonging to the Dutch East 

 India Company. And communicated hy Mr. Boyle. N° 97, p. 61 15. 



Ambergris is not the scum or excrement of the whale, &c. but issues out of 

 the root of a tree ; which tree, how far soever it stands on the land, always 

 shoots forth its roots towards the sea, seeking the warmth of it, thereby to de- 

 liver the fattest gum that comes out of it : which tree otherwise by its copious 

 fatness might be burnt and destroyed. Wherever that fat gum is shot into the 



♦ Ambergris or ambergrease, is now pretty generally allowed to be no other than the hardened 

 faeces of the sperma-ceti whale, or physeter macrocephalus of Linnaeus. Of this particular an ample 

 account occurs in volumes 33, 38, and 90 of the Transactions, and will of course be abridged in a 

 fiiture volume of the present work. 



