IET. XV.

OF THE EARTH.

245

unit, to which he refers all the parts of theuniverse.

By means of chains and cords, which arecertain multiples of the toife, or the yard, heobtains an artificial measure more convenientthan the natural one; and with this new stand-ard, repeated a certain number of times, in thefame manner as before, he forms furlongs, milesand leagues, and undertakes to measure suchdistances, as would be otherwise indeterminable.But this method is yet totally inadequate tothe purpose required; for if it were necessaryto follow the whole circumference of the earth,in order to obtain its measure, the thing wouldbe impossible; mountains, rivers and seas, wouldbe perpetual obstacles in our way; and uninha-bitable climates would put an entire stop to ourprogress. In order, therefore, to surmount thesedifficulties, we must have recourse tp Astrono-my, which furnishes us with a method of mea-suring the whole terraqueous globe, without thenecessity of quitting oqr country, or even losingsight of our native habitations.

But let us leave this part of the subject forthe present, and attend to the steps which led toso important a discovery. It was the commonlyreceived opinion, even so late as the fifteenthcentury, that the earth was a flat body, infi-nitely extended, and covered by the sky, in theform of a vault or tent. And as this doctrineR 3 had