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whole of the Northern Hemisphere in the upper room. The floor on which you stand is the Equator; and the Southern Hemisphere will be disposed of in like manner in the lower room; only remembering to reckon downwards for South Latitude.
But the most simple method is this:—The globular Map of the World being familiar to all who have the slightest knowledge of Geography:—Divide each Hemisphere into quarters, and either obliterate the figures which mark the longitude (from meridian of Greenwich), or substitute a scale of your own, counting Greenwich 20 East, and onwards to 180 in the Eastern Hemisphere, so that you gain 20 degrees East Longitude, which amount must be subtracted from the former, in order to its agreeing with the common mode of reckoning. According to our plan, for degrees under 20 in the Eastern Hemisphere, deduct their amount from 20, and the remainder is Longitude West; thus, 17 from 20, remains 3 West. And by the same method you lose in counting 20 degrees from the Western Hemisphere, in Longitude West, which amount you will add for a similar reason, until we come to 160 West Longitude; thus—
| West Longitude | East | |
| 165 | (our plan) is | 175 |
| 170 | . . . . . . | 170 |
| 175 | . . . . . . | 165 |
| 180 | . . . . . . | 160 |
Or, more particularly, our plan, Longitude West from 160 to 170 degrees, double the Unit of the Degree, and add the difference between that amount and 20; thus, 161, (the 1 being doubled (2), leaves 18; which, added to 161, is 179, Meridian of Greenwich; and this process is exceedingly easy, observing that all under 20 degrees in your Eastern Hemisphere is West Longitude from Greenwich; aud every degree above 180 in the Western is East
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