GEODÆSIA Improved. 275

it were to be wished that all those Surveyors who are equally wed-ded to, and prepossessed in Favour of Instruments, i. e. the Theo-dolite, Circumfcrentor, Semi-circle, &c. were less partial andmore charitable in their Reflections against the plane Table andits Adherents. I fay let them not contemn a Method since theirsis scarce advanced one Step nearer the Truth, as will appearanon. To censure those of the same Profession administers noadditional Credit to the Character of any Man; let not,therefore, any Person conscious of his Error be guilty of throw-ing the first Stone, but always favourably speak, and chearfullyassist (if required) a Brother Concomitant; whoeverthus deportthemselves, will, in the End, (if mt before) reap the Advan-tage thereof.

Of the Variation of the Needle, and how to reliify your Meridian.

1. The Variation of the Needle, or Compass, is an Arch ofthe Horizon, intercepted between the Solstice and magneticMeridian, either easterly or westerly, and cannot exceed 90Degrees.

2. The Variation is easterly when the magnetic Pole is to theEast of the North Pole, but if it lie to the West, then the Va-riation is westerly.

3. Magnetic Poles are two (imaginary) moving opposite Points,which revolve about the Poles of the World nearly 9 Degreesdistant therefrom, and compleat their Revolution in about 600Years, which occasions the Variation of the Needle.

4. Magnetic Meridian, is a great Circle passing through themagnetic Poles, to which Meridian the Needle hath Respect, ifnot otherwise obstructed.

5 The Variation of the Needle may be found by an Ampli-tude or Azimuth, to find which you must have the Latitude ofthe Place, the Declination of the Sun, and magnetic Ampli-tude thereof.

6. The