NEW REFLECTING QUADRANT. 219 



index glafs, m the horizon glafs, and H E the line of fight, or 

 axis of the telefcope. Upon this line of fight, at an angle of 

 45 degrees, let another horizon glafs be fixed, reprefented by 

 x y, which may be called the fecond horizon glafs. 



When a ray of light R n falls upon the centre of the glafs 

 xy, at an angle of 45 degrees, it will be reflected to the eye 

 at E ; becaufe the angle x n E (the angle of reflection) is = 

 45° by conftruction, and confequently RrcH and RwEare 

 right angles. 



The Ufe of the Befiecling Quadrant in taking Angles. 



All angles lefs than 90° are to be taken by this inftrument, Manner of ufing 

 in the fame manner as by the fextant. But, fuppofe it were ,u 

 required to obferve the fupplement of the fun's meridian alti- 

 tude at fea, let the axis of vifion be directed to the zenith, 

 and turn the quadrant till that part of the horizon, which is 

 oppofite to the fun, be feen by reflection from the fecond ho- 

 rizon glafs ; then turn the index from towards M, till the 

 fun appears in the telefcope, with one of its limbs in contact 

 with the horizon, and the index will fliew the fun's obferved 

 zenith diftance ; to which add 90°, and the Aim will be = 

 the angle obferved by the quadrant, = the obferved fupple- 

 ment of the fun's meridian altitude. 



To adjujl the Second Horizon Glafs. 



Let the arc L N be made equal to the arc L M, and gra- Adjuftment. 

 duated from 0° at L, to 90° at N. Then, after the index 

 error has been determined, kt the index to 90° at N, and 

 elevate the telefcope till the fun, or fome other remote object, 

 be feen by reflection from the index and horizon glafles, and 

 the fame object will alfo be feen by reflection from the fecond 

 horizon glafs : confequently, the angle RnH becomes known » 



to as great a degree of precifion as the index error. 

 I am, 

 SIR, 



Your obedient fervant, 



EZEKIEL WALKER. 

 Lynn Regis, Feb, 20, 1803* 



V. Mifcellaneous 



