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fuch length in an horizontal diredion as to be feen, when no 

 telefcope is nfed, in the filvered and unfilvered parts of the 

 horizon glafs, will ferve for the adjuftment, provided the eye be 

 fixed, by having the quadrant immoveably placed on a ftand, or 

 faftencd to a board while the adjuftment is performing ; fo that 

 it may thus be very ealily and accurately effedcd at any time 

 even within doors, (care being taken that the floor of the room 

 does not by fpringing or bending change the relative altitudes of 

 the level and objed from the ground, and their angular diftance) 

 by fixing up as an objed a ftrip of black paper or any kind of 

 foil, &c. on a pane of the window, extended horizontally : and a 

 fmaWJixed telefcope, furnifhed with crofs wires fet diagonally in 

 the tube, (that the horizontal image may appear within the angles 

 at the centre) and the wires placed at fuch a diftance from the 

 eye-glafs, that a motion of the eye will not afFed the apparent 

 place of the image in the field of view, rhay be fubflitutcd inftead 

 of the quadrant, if it be more convenient to do fo ; the manner 

 of performing this adjuftment is defcribed underneath*. 



It 



* Unlefs the adjuftment by a near objeft be condufled in a judicious manner, a 

 perfon may weary himfelf in doing it, where yet there is no difficulty. Let the qua- 

 drant be fo fixed on a ftand pr rather to an upright board, on which is fattened the 

 arm K fupporting the level, that the two images may by the motion of the index, &c. 

 be brought to coincide near the middle of the mirror : the mirror may then be Crft 

 turned round on the needle, 'till fome certain diameter of it, as fuppofe that in the 



diredion 



