i88 5 .] 
The Form of the Earth. 325 
It having become an accepted and popular theory, that 
the Earth when in a fluid state had rotated on its axis, and 
as a consequence had assumed a spheroidal form, it was 
decided that arcs of the meridian should be measured in 
various parts of the world, in order to prove the accuracy of 
the theory. Now let us ask what the observers who were 
sent on these expeditions were expected to accomplish ? 
They were expected to measure a base line, and from this 
base line to extend a triangulation to the extent of nearly 
70 miles. They were then to determine two points north 
and south of each other, which were exactly i° apart. 
Let us first deal with the surveyors’ part of the work, 
viz., the measurements, and we find that the surveyors had 
to measure 365,000 feet without an error of 1000 feet, or even 
100 feet. This in itself is a work of great difficulty, and 
one which the surveyors of former times, especially in a 
rough country, could not fairly accomplish. 
Next we have the astronomical problem to consider. The 
latitude of two points is to be ascertained to within T', and 
with portable instruments. What are the probabilities of 
this being practically accomplished ? With the most perfect 
instruments, and thousands of observations made each year, 
the latitude of Greenwich Observatory fifty years ago was 
2" in error ; that is, the latitude then assigned to the 
Observatory differed 2" from that which is now assigned 
to it. 
A second of latitude may be taken as about 120 feet, — 
consequently 2" would be about 240 feet. This error at 
each station would amount to 480 feet, and this error might 
occur after a hundred years of observation and with the 
most perfect instruments. A far greater uncertainty must 
exist when observations were made during only a few 
months, or years, and with instruments inferior to those now 
in use at Greenwich. To claim, therefore, that observers 
one hundred years ago proved that a degree of the meridian 
measured near Peru or at the Cape was a certain number of 
feet shorter than a degree of a meridian measured in 
England, is one of those pleasing but visionary delusions 
in which theorists too often indulge. 
But afar more amusing delusion exists in connection with 
certain measurements made in former times to ascertain the 
tenth millionth part of go 0 of latitude. The French being 
anxious to introduce an exaCt standard of measure, viz., a 
tenth millionth part of the arc from the Equator to the Pole, 
employed several surveyors and astronomers to measure arcs 
in various parts of the world. These observers, as was 
