( 171 ) 
' The Bore of the fmall Pipes land K, and the Tube 
H, mud not be fo narrow as to make it difficult to 
reduce the Spirit into its Place, if by any Accident 
either End of it (hould get into them. 
1 have been informed, that an ObjeQ: may be kept 
in View without much Difficulty, even in pretty 
roughWeather,thro’ aTelefeope magnifying about ten 
times. Now as fuch Telefcopes feldom comprehend 
an Area of much more than one Degree in Diameter, 
or at mod i Deg. 20 Min. it follows that the Axis 
of the Telefcope is always kept within 40 Min. at 
mod of theObjed, and that is the greated Vibration 
of the Image above and below the Thread on the Vane. 
If this be allowed, it feems reafonable to exped: 
that the Medium of the Vibrations one Way Ihould 
not exceed the Medium of thofe the other, more 
than by about one fifth or one fixth Part of the great- 
ed Vibration ; i.e. about 7 or 8 Min. the half of 
which will be the Error of the Obfervation. In 
dill Weather it will probably be much lefs, if the 
Indrument be in the Hands of a Perfon moderately 
Ikilful in obferving. 
III. Tie Anatomy of a Female Beaver, and an 
Account of Caftor found in her. Tty C. Mor- 
timer, M. T>. % S. Secret. 
I N the AEta Erudit. Menfe Aug. 1684, P a g- 360, 
& feq. I find the Account of the Diifedion of a 
Male and Female Be aver by E. G. H. who midakes, 
in opening the Male, the Receptacles of the Caftor 
for the Uterus , and the two Glands below them for 
Dugs i 
