MEASURING THE EARTH'S SURFACE. 245 



The progress made by mathematical science during the seventeenth 

 and eighteenth centuries, and the great controversy raging then con- 

 cerning the exact form of the earth, resulted in a serious attempt being 

 made to measure arcs of the meridian at different places on the sur- 

 face of the globe, and as much as possible near the central parallel, the 

 equator, and the extreme parallel that could be reached, the polar cir- 

 cle. This work was undertaken by the French Academy of Sciences, 

 and two expeditions were fitted out to undertake such measurements, 

 one in Sweden and the other in Peru. The execution of the work was 

 very accurate, considering the difficulties under which it was under- 

 taken. Their purpose was to obtain the exact length of a degree at 

 those different latitudes, and from these lengths the exact form of the 

 earth. The results of the work done by the two expeditions were 

 made known about the year 1750, and showed that the length of a 

 degree near the equator was shorter than that of a degree in a north- 

 ern latitude, the difference, expressed roughly and in a popular man- 

 ner, being a little less than one per cent. This confirmed the theory 

 which had been previously proposed, that the earth was depressed near 

 the pole, so that, although this theory had been already advanced be- 

 fore the end of the seventeenth century, it was not generally accepted 

 until it was shown to be correct by actual measurement. The im- 

 petus given to geodetical measurements by the last-named expedi- 

 tions and by the results obtained was so great that geodetical work 

 began to be done in earnest. The English triangulation was begun 

 before the close of the last century. In India a short arc measure- 

 ment was also executed about the same time. 



The outbreak of the French Revolution, and the new ideas which 

 it gave rise to, were the direct cause of the most interesting scientific 

 work done at the close of the last century. As they abolished the privi- 

 leges of classes, the new ideas tended also to abolish the privileges of 

 systems, and a new system of computation was tried to be introduced 

 which would give uniformity in division. This division was the deci- 

 mal instead of duodecimal or others which had been until then the 

 prevailing ones. Thus the year was divided into twelve months, and 

 the month into three weeks of ten days each, the tenth day being made 

 a civil holiday ; the remaining five days of the year not being distrib- 

 uted in the various months, as with the Gregorian Calendar, but being 

 put together as a civic yearly period of festivity at the end of the 

 year, which was made to begin with the September moon, on the 

 twenty-second day of September. The same was done as regards the 

 system and units of measurement, value, etc. ; but, while the time- 

 divisions were made on a rather arbitrary basis, and have, therefore, 

 not been able to supersede the older and more natural divisions, the 

 decimal system of measures, weights, and values which was then in- 

 troduced, rested on a thoroughly scientific basis, and has therefore 

 been able to withstand all attacks and to gain introduction into the 



