TOL. VII.] PHILOSOPHICAL TRANSACTIONS. 



733 



An Account of some Boohs. N" 84, p. 4095. 



I. An Essay about the Origin and Virtues of Gems ; by R. Boyle, Esq. F. R.S. 

 1672, in 8vo. 



The design of this essay is to prove, 1st. That most gems and medical stones 

 were either once fluid bodies, or in part made up of such substances as were 

 once fluid ; and 2dly, That the real virtues of such stones are probably derived 

 from the mixture of metallic or other mineral substances with which they are 

 usually impregnated. 



II. Johannis Swammerdami, M.D. Uteri Muliebris Fabrica, &c. Lugduni 

 Batav. 1672, in 4to. 



Besides a description of the organs of generation in women, and an inquiry 

 into the mode of impregnation and conception, there are in this tract some ob- 

 servations on the force of the imagination in breeding women, and an account 

 of a method of injecting the blood vessels with wax variously coloured. 



III. Three letters of Jo. Dom. Cassini, concerning his Hypothesis of the 

 Sun's motion, and his doctrine of Refractions ; printed at Bononia, in 4to. 



The first letter is to G. Montanari, professor of mathematics in Bononia. 

 His former hypothesis was grounded on observations of the sun, from whose 

 altitudes, when they were great, he made no abatement ; because, according to 

 the common opinion, the refraction is nothing, or at least inconsiderable. A 

 specimen of it was published about \Q years ago. But afterwards he changed 

 that hypothesis, that it might agree with his observations as diligently made, 

 and more corrected. For having determined the height of the pole (and there- 

 by of the equinoctial,) at Bononia; he observed also the sun's meridian height 

 in both solstices. And subtracting that winter height from that equinoctial's 

 height ; and the said equinoctial's height from the summer height, he always 

 found that former difference less, by above 4 minutes and a half, than the latter 

 difference. Wherefore he attempted to order the parallaxes and refractions so, 

 as that those summer and winter observations, being corrected according to that 

 doctrine, might yield the sun's southern greatest declination, equal to the sun's 

 greatest declination northward. In this letter he sets down what course he 

 took to find the refractions ; what experiments he made in glass and in water; 

 how he applied them to celestial refractions ; his proceeding to determine the 

 proportion of the height of the air to the semidiameter of the earth ; and at last 

 to make tables to single degrees of apparent distance from the vertex. 



The second letter is to Carlo Rinaldini, professor of mathematics in the 

 university of Padua, dated August T , 1666. — In it he shows some defect in the 



