126 PHILOSOPHICAL TRANSACTIONS. [aNNO 1674. 



colour like burnished gold. I broke one or two of them with some difficulty, 

 and I found by the microscope, that it was only a thin shell that was so orient 

 and bright, the inner side of which shell was like unpolished gold : the inmost 

 substance was like brown sugar-candy to the naked eye, but not so transparent: 

 the taste was not discernible. In spirit of vitriol they shrunk much and wasted, 

 but continued their colour. Likewise aqua fortis would corrode and dissolve 

 them tumultuously. 



York, March 12, 1 67 3-4. 



On the Origin of Pearls. Bij M. Christ. Sandius. N° 101, p. 11. 



The pearl shells in Norway, and elsewhere, breed in fresh water. Their 

 shells resemble those commonly called muscles, but they are larger. The fish in 

 them looks like an oyster, and it produces a great cluster of eggs, like those of 

 crawfish, some white, some black, which latter become white, the outer black 

 coat being taken off. These eggs, when ripe, are cast out, and then grow, 

 becoming like those that cast them. But sometimes it happens, that one or 

 two of those eggs stick fast to the sides of the matrix, and are not voided with 

 the rest. These are fed by the oyster against its will, and they grow, accord- 

 ing to the length of time, into pearls of different sizes, and imprint a mark both 

 in the fish and the shell. 



This account M. Sand had from a Dane, called Henry Arnoldi, a person, he 

 says, of veracity, and who had made the observation himself, at Christiana, in 

 Normandy. [This Mr. Arnoldi had a very erroneous notion concerning the no- 

 tion of pearls, which are certainly not the eggs of certain muscles and other 

 bivalves, in which they are found.] 



An Account of some Boohs. N° 101, p. 12. 



I. An attempt to prove the Motion of the Earth from Observations, made by 

 Robert Hook, F. R. S. London, in 4to, 1674. 



The ingenious author of this attempt, having considered with himself, that 

 the grand controversy about the earth remains yet undetermined ; and finding 

 Ixiere w as no better means left for human industry to decide it but by observing, 

 whether there be any sensible parallax of the earth's orb among the fixed stars; 

 did thereupon resolve to employ himself in making some observations concern- 

 ing so important a point in astronomy. His method, which he gives an account 

 of, is to observe by the passing of some considerable star near the zenith of 

 some place, whether such a star does not at one time of the year pass nearer to 

 the zenith, and at another farther from it. 



Accordingly he affirms to have actually made four observations ; by which, 

 he says, it is manifest, that there is a sensible parallax of the earth's orbit to the 



