The horizontal lines are parallels of latitude, and the perpendicular lines are meridians or circles of longitude.
The series of walls in the first room will be as follows:
| I. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| II. | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 |
| III. | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 |
| IV. | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 |
Upon referring to the globe, it will be found that the whole hemisphere, north of the equator, has been transferred into the first or upper room; the southern hemisphere being reserved for the room beneath.
Before we proceed further, the meridian must be fixed. This, in English charts, is taken from London, or more correctly from Greenwich, counting the longitude east and west from that place. The French place their meridian in Paris, but they mark also in their maps the longitude from Ferro, from which island, all the other European nations commence theirs; by these means, the longitude which is laid down on a foreign map is comprehensible by them, and the Parisian mode is easily understood by any
