222 PHILOSOPHICAL TRANSACTIONS. [anNO I697. 



where some of his wool is become white, down to his knees, he is every where 

 dappled with white spots, some of which are broader than the pahn of a man's 

 hand. They are very white, at least equal to the skin of the fairest lady. But 

 of a paler white, and do not show flesh and blood so lively through them as 

 the skin of white people ; the reason of which may be, that the skin of a 

 negro is much thicker. His face, arms, and legs, are perfectly black. 



Surprising Effects of a terrible Clap of Thunder with Lightning, that fell on the 

 Trumbull Galley, on Thursday the iQth Day of Noveinber, 1696. Commu- 

 nicated by Mr. Robert Mawgridge, Surgeon ofthesaid Galley. N° 235, p. 782. 



The vessel was violently struck, and greatly damaged, but none of the people 

 killed. Some of the masts and yards shivered to pieces, and many parts of the 

 hull blown out. 



Part of a Letter from Mr. Halley, dated Chester, Oct. 25, l6y7 ; giving an 

 Account of his Observations there of the Eclipse of the Moon, Oct. 1 g. N° 235, 

 p. 784. 



I observed the eclipse with all the satisfaction I could desire, the air was all 

 the while very still and clear : so that I think the observation may be very much 

 depended on, and will, with sufficient exactness, give the longitude of this 

 place. 



The beginning 6h. S-^m. the end 8h. AQ\m. 



About the middle there remained 9' 26' of the luminous part, and conse- 

 quently the digit eclipsed, Sf. 



Experiments about making Concave Specula nearly of a Parabolic Figure. By 

 Mr. Stephen Gray. N° 235, p. 787. 



A linen cloth being first wet in fair water, and then laid on a concave cylinder, 

 as the verge of a sieve, or the like, its central parts will descend, so as to form 

 a very regular concave superficies, which I suspected to be a parabolical, well 

 known to be the best of figures, could it be obtained for burning glasses, in 

 which I was not greatly deceived. A thread, being first wet in common water, 

 and then suspended with its two ends, or any two points nearer than their 

 utmost extent ; so as to touch the centre of the suspended cloth, and its tvvo 

 opposite points on the ring, was found to have the same curvature : as indeed 

 could scarcely be doubted, since the cloth is but a number of threads suspended 

 in the position of this single one. To discover the figure of the thread, thus 



