VOL. XXII,] PHILOSOPHICAL TRANSACTIONS. 527 



phragma, the pleura, and to the sternum, in which it had dug 2 great holes, so 

 strong was the impulsion. The inside of the bag was lined almost all over with 

 bony laminae, some larger, some less, like so many shells. The heart was 

 greatly relaxed, insomuch that it was twice as large as it ought to be. And 

 among its fibres there were some stones, like those sometimes found in the 

 lungs of scrophulous bodies. 



Account, of Mr. Samuel Brounis second Booh of East India Plants, with their 

 Na7nes, Tlrtues, Description, &c. By James Petiver, Apothecary, andF.R.S. 

 N°267, p. 699. 



An enumeration and description of 44 more East-Indian plants, gathered by 

 John Osmond on the 27th and 28th of April 1696, at Pearmeedoor, about ]6 

 or 17 miles from Fort St. George, (Madras.) To the Malabar names Mr. 

 Petiver adds the synonyms of Plukenet, Ray, and other botanists. 



To determine the Colours and Diameter of the Rainhoiu, from the given Ratio of 

 Refraction; and the contrary. By Edm. Halley, F.R.S. N°267, p. 714. 

 Translated from the Latin. 



To those who have attentively considered the phaenomena of the rainbow, it 

 has always been nianifest that the sun's rays, reflected by a watery cloud, have 

 entered the eye at some certain angle : whence proceeds its form of a bow. But 

 the reason of its colours, as also of the magnitude of that angle, by which we 

 find the rainbow constantly to be distant from the point opposite to the sun, has 

 given much trouble both to the ancients and moderns. 



Nor did they do any thing to the purpose, till the famous Des Cartes, calling 

 to his assistance the mathematical sciences, informed us by many examples, that 

 these physical speculations might and ought to be treated in a stricter method of 

 argumentation. And among other things he has given us the tiieory of the 

 rainbow. From his demonstrations it is plain, that the primary iris is produced 

 by such rays of the sun, in which the excess of the two refracted angles above 

 the one angle of incidence, is the greatest of all possible angles. That the se- 

 condary iris is formed by those rays only, in which the excess of the three re- 

 fracted angles above the one angle of incidence, in like manner is the greatest 

 possible. And so we might go on to the third, fourth, or any other iris, which 

 are made when the rays emerge, out of the drops, after three, or four, or more 

 reflexions. Now in all these there is a general rule, that the excess of four, or 

 five, or more refracted angles, (that is, the number of reflexions must t^e in- 

 creased by an unit,) above one angle of incidence, must be the grea.'est of all. 

 Now that greatest excess being doubled, is always the distance of the iris from 



