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Example II. — I wifh to know the variation of a plan’smeridian, when the bearing of two objects thereon withits meridian is north 16° eaft, ■and the bearing of thefame two objects with each other on the furfacc is found,by an inftrunrent whofe needle has 23 0 of welt variation,to be north io° eaft ?

The objects on the furface will form a bearing witheach other of north 13 0 weft by the true meridian.

Then (per rule 2d) 16 0 -f- 13 0 = 29 0 ; therefore theplan’s meridian has 29 0 of weft variation. '

Example III. — I have a plan which I wifh to knowby what kind of meridian it has been delineated : Nowthe bearing of two objedts thereon with each other by itsmeridian is found to be north 8o° weft, and the bearingof the fame two objects, taken on the furface by an in-ftrument whofe needle has 21 0 of weft variation, is north74 0 weft ?

The* bearing of the two objects on the furface with thetrue meridian will be fouth 85° weft.

Then (per rule 3d) x8o° — 8o° + 05° =15°; there-fore the plan has been delineated by a meridian having15 0 of weft variation.

Example IV.—I wifh to know the variation of a plan’smeridian, when the bearing of two objects taken thereonby its meridian is found to be north 40° eaft, and thebearing of the fame two objects, taken on the furface byan inftrument whofe needle has 20° of weft variation, isalfo north 40° eaft ?

Then (per rule 4th) the meridian of the plan will havethe fame magnetic variation as the needle by which the

bearing