VOL. XXXVIII.] PHILOSOPHICAL TRANSACTIONS. 023 



about 10 times. Now as such telescopes seldom comprehend an area of much 

 more than l" in diameter, or at most 1° 20', it follows, that the axis of the 

 telescope is always kept within 40' at most of the object, and that is the greatest 

 vibration of the image above and below the thread on the vane. If this be al- 

 lowed, it seems reasonable to expect that the medium of the vibrations one 

 way, should not exceed the medium of those the other, more than by about -Lth 

 or ith part of the greatest vibration; i. e. about 7 or 8 min. the half of which 

 will be the error of the observation. In still weather it will probably be much 

 less, if the instrument be in the hands of a person moderately skilful in 

 observing. 



The Dissection of a Female Reaver, and an Account of Castor found in her. 

 Bi; C. Mortimer, M. D. R. S. S. N° 430, p. 172. 



In the Acta Erudit. for Aug, l684, p. 360, et seq. Dr. M. remarks that there 

 is an account of the dissection of a male and female beaver by E. G. H. who 

 mistakes, in opening the male, the receptacles of the castor for the uterus, and 

 the 2 glands below them for dugs; and as they found a penis and testicles in 

 the same animal, it was concluded to be an hermaphrodite : but on dissecting 

 the female, they found a uterus, with 2 horns like that of bitches, besides the 

 receptacles of the castor, which he should have thought sufficient to have set 

 the author to rights, as to the former beaver being an hermaphrodite. 



Johannes Francus, a German physician, has published a Treatise, called Cas- 

 torologia explicans Castoris animalis naturam et usum medico-chemicum, Au- 

 gust. Vindel. l685, Bvo. being a Commentary on a Treatise formerly written 

 by one Johan. Marius, a physician at Ulm. In this. Sect. 7, Marius describes 

 the receptacles of the castor, as being bags near as large as a goose-e^g; 

 and that they have been erroneously called the testicles, being in females as 

 well as males, but that they have no communication with the pudenda. His 

 commentator Francus recites the opinions of some modern writers, who are 

 still in the old error as ancient as ^Elian, who says, that the beaver bites out 

 his own testicles, when pursued by the hunters, as if he were conscious those 

 were the parts his persecutors want, and seek his life for. He cites Adam 

 Zwiker, as having this notion, and likewise Job. Harder and Joh. Schappler ; 

 nay, some have thought so absurdly, as to imagine that the beaver had 4 tes- 

 ticles : and he says, that Gulielmus Rondeletius was the first person who dis- 

 sected a beaver with accuracy sufficient to refute the old error ; showing that 

 the castor was not the testicles, but peculiar bags lying in the groin. 



Marius, Sect. Q, savs, that beavers are found in the Hera, and the Danube. 



