FORM AND CONSTITUTION OF EARTH—STEWART. 163 
was dispatched northward and another southward, each with instruc- 
tions to measure as they went and continue their work until the 
altitude of the pole was observed to have changed by 1°. The 
northern party found 56 miles and the southern party 562 miles 
as the length of 1°. The English equivalent of the latter value, 
which was accepted as being the most accurate, is about 71 miles. 
It was not until the sixteenth century that Europe, having 
awakened from the lethargy of the Dark Ages to new intellectual 
life, entered upon the era of development of which we have not yet 
seen the end. Among the various activities in which this newly 
found energy sought an outlet may be noted the exploration of 
foreign lands. America had been discovered, and in 1521 Magellan 
had completed the circumnavigation of the globe; and it may have 
been this latter achievement that turned men’s attention to the 
problem of determining the earth’s dimensions. 
In 1525 Jean Fernel, court physician to Henry IJ of France, and a 
cultivator of. the mathematical sciences, measured the length of a 
meridian arc near Paris. His method was so crude as to be but a 
slight advance upon those of the ancient astronomers which have 
already been considered. He measured the length of his are by 
counting the revolutions of a carriage wheel while driving from one 
end of it to the other; and his astronomical observations were made 
with a triangle used as a quadrant. He found the length of 1° to be 
365,088 feet, a result very near the truth. 
It is not proposed to give an exhaustive account of all the geodetic 
surveys of the last three centuries, but only to notice briefly those 
that embodied some improvement in method or were important 
in their results. 
A great advance upon previous methods was now for the first 
time made by Snellius, who employed the method of triangulation 
to measure the length of a meridian arc, the method which has been 
in use ever since, and is superior to all others on account of its accu- 
racy and cheapness, combined with adaptability to any country, 
whatever its nature. He measured a base with a chain between 
Leyden and Soeterwood, and his chain of triangles, 33 in number, 
extended from Alemaar to Bergen-op-Zoom. This distance, pro- 
jected upon a meridian, gave a meridian are having an amplitude 
of 1° 11’ 05’’, which made the length of 1° to be 55,074 toises, a toise 
being equal to 6.3946 English feet. His angles were measured with a 
graduated semicircle 34 feet in diameter, and his latitudes observed 
with a quadrant 53 feet in diameter, neither of these instruments 
being provided with a vernier or telescope sight, as neither had been 
invented at that time. It was not to be expected under those cir- 
cumstances that his result would be remarkable for precision, in 
spite of the precautions which he took to secure it; in fact, his length 
