( M« )

To find the variation ofi the meridian of a plan, when the angleof the bearing of two objects thereon with the plan s meri-dian, and the angle of the bearing of the fame two objects onthe furface with the true meridian, bear on the fame fide ofeach refpeElive meridian.

Rule I.—Find the number of degrees contained inthe angle that the bearing of two objedfs on the planmakes with its meridian, and alfo the degrees in the an-gle that the fame objedts on the furface make with thetrue meridian, and their difference will be the number ofdegrees contained in the magnetic variation of the plan’smeridian ; which variation will be on the fame fide ofthe true meridian as the objedls were found to bear withthat meridian, if the angle formed by the bearing of theobjedts on the plan with its meridian is lefs than the an-gle that the fame objedts on the furface form with thetrue meridian : .Or, if the angle formed by the objects onthe plan is greater than the angle that the fame objectsform with the true meridian, the variation will be on thecontrary fide of the true meridian that the objedts bearon'with that meridian. Thus, if the bearing of any twoobjects on a plan by its meridian is found to be north40° weft, and if the fame two objedts on the furface, ta-ken by an inftrument whofe needle has 23 0 of weft varia-tion, be found to bear north 27 0 weft, or north 27 0 +23 0 = 50° weft with the true meridian, then (per rule)50° — 40° = io°, the variation of the plan’s meridian.Now the angle formed by the objedts on the plan withits meridian is lefs than the angle that the fame objedtsform with the true meridian on the furface; alfo the

bearing