That degree upon the equator which is cut by the brazen meridian, is the Longitude required from the first meridian upon the globe. If the longitude is counted both ways from the first meridian upon the globe, then we are to consider, whether the given place lies Easterly or Westerly from the first meridian, and the longitude must be expressed accordingly.
The Latitudes of the following places: and upon a globe where the longitude is reckoned both ways from the meridian of London, their longitudes will be found as follow:
| Latitude. Deg. | Longitude. Deg. | |||
|---|---|---|---|---|
| Rome | 41¾ | North. | 13 | East. |
| Paris | 48¾ | N. | 2½ | E. |
| Mexico | 20 | N. | 102 | W. |
| Cape Horn | 58 | S. | 80 | W. |
2. The Latitude and Longitude being given to find the Place.
Seek for the given longitude in the equator, and bring that point to the meridian; then count from the equator on the meridian the degree of latitude given, towards the arctic and antarctic Pole, according as the latitude is Northerly or Southerly, and under that degree of latitude lies the Place required.
Prob. II. To find the Difference of Latitude betwixt any two given Places.
Bring each of the places proposed successively to the meridian, and observe where they intersect it, then the number of degrees upon the meridian, contained between the two intersections, will be the Difference of Latitude required. Or, if the places proposed are on the same side of the equator, having first found their latitudes, subtract the lesser from the greater; but if they are on contrary sides of the equator, add them both together, and the difference in the first case, and the sum in the latter, will be the difference of latitude required.
Thus the difference of latitude betwixt London and Rome will be found to be 9¾ degrees; betwixt Paris and Cape Bona Esperance 83 degrees.