CELESTIAL MEASURINGS AND WEIGHINGS. 187 



new triangles on all sides, of larger and larger dimen- 

 sions ; till the whole surface of a kingdom or a continent 

 becomes covered with a network of them, all whose 

 angular points are precisely determined. The strides 

 so taken, moderate at first, become gigantic at last : 

 steeples, towers, obelisks, mountain cairns, and snowy 

 peaks, becoming in turn the stepping-stones for further 

 progress ; the distances being only limited by the range 

 of distinct visibility of objects through the haze of the 

 atmosphere. Even this is extended by artificial means 

 by Bengal lights at night and by the use of the " helio- 

 trope," a contrivance of the celebrated Gauss for reflect- 

 a strong sunbeam from station to station ; by the use of 

 which, stations 90 or 100 miles distant have been brought 

 into direct connexion. 



(12.) If the earth's surface were a plane such a process 

 might be continued adinfinitum. The general roundness 

 of the earth, however, has been recognized as a fact from 

 very early ages ; and indeed it is scarcely possible for 

 any thinking person, with ever so slight an acquaintance 

 with the most elementary geometry, not to be aware of 

 it. It was not, however, till about some three centuries 

 before our era, that something like just notions of its 

 actual size were entertained : unless we admit (an opinion 

 which has found strenuous defenders) that this important 

 datum was already exactly known to the ancient Egyp- 

 tians 1800 years previously;* a fact, iftme, all memory 



* The height of the great pyramid from base to apex is (tvas) con- 

 tained exactly 270,000 times in the circumference of some one diame- 

 trical section of the earth. 



