VOL. XLII.] PHILOSOPHICAL TRANSACTIONS. 5QI 



and 4- minutes, ab is a telescope, 3 or 4 feel long, fixed on thq edge of that 

 brass plate, g is a speculum, fixed on the brass plate perpendicularly, as near 

 as may be to the object-glass of the telescope, so as to be inclined 45 degrees 

 to the axis of the telescope, and intercept half the light which would otherwise 

 come through the telescope to the eye. CD is a moveable index, turning about 

 the centre c, and, with its fiducial edge, showing the degrees, minutes, and 

 -y minutes, on the limb of the brass plate pa ; the centre c must be over-against 

 the middle of the speculum g. h is another speculum, parallel to the former, 

 when the fiducial edge of the index falls on 0° O' O* ; so that the same star may 

 then appear through the telescope, in one and the same place, both by the 

 direct rays and by the reflexed ones; but if the index be turned, the star 

 shall appear in two places, whose distance is showed, on the brass limb, by 

 the index. 



By this instrument, the distance of the moon from any fixed star is thus ob- 

 served : view the star through the perspicil by the direct light, and the moon 

 by the reflexed (or on the contrary) ; and turn the index till the star touch the 

 limb of the moon, and the index shall show, on the brass limb of the instru- 

 ment, the distance of the star from the moon's limb ; and though the instru- 

 ment shake, by the motion of the ship at sea, yet the moon and star will move 

 together, as if they did really touch one another in the heavens ; so that an ob- 

 servation may be made as exactly at sea as at land. 



And by the same instrument, may be observed, exactly, the altitudes of the 

 moon and stars, by bringing them to the horizon ; and thereby the latitude, 

 and times of observations, may be determined more exactly than by the ways 

 now in use. 



In the time of the observation, if the instrument move angularly about the 

 axis of the telescope, the star will move in a tangent of the moon's limb, or of 

 the horizon ; but the observation may notwithstanding be made exactly, by 

 noting when the line, described by the star, is a tangent to the moon's limb, 

 or to the horizon. 



To make the instrument useful, the telescope ought to take in a large angle : 

 and to make the observation true, let the star touch the moon's limb, not on 

 the outside of the limb, but on the inside. 



The Effects of Cold ; with Observations of the Longitude, Latitude, and Decli- 

 nation of the Magnetic Needle, at Prince of Wales's Fort, on Churchill river 

 in Hudson s Bay, North America. By Capt. Christopher Middleton, F.R.S. 

 1741-2. N°465, p. 157. 

 Capt. M. observed, that the hares, rabbits, foxes and partridges, in Sep- 



