Page:Popular Astronomy - Airy - 1881.djvu/76

62 means of determining accurately the dimensions of the earth. There is also one measure which is worth mentioning, on account of the extraordinary times in which it was effected. It was the great measure extending from Dunkirk, in France, to Barcelona, in Spain, and which was afterwards continued to Formentera, a small island, near Minorca. It is worth mentioning, because it was done in the hottest times of the French Revolution. We are accustomed to consider that time as one purely of anarchy and bloodshed; but the energetic Government of France, though labouring under the greatest difficulties, could find the opportunity of sending out an expedition for these scientific purposes; and thus did actually, during the hottest times of the revolution, complete a work to which nothing equal has been attempted by England.

Now, from all these measures put together, we are able to infer a proportion of the axes of the earth, and we are able to try whether all these different measures agree well with the supposition that the earth is a spheroid. There is a quantity of mathematical calculations concerned in it; the problem is this: suppose the earth to be a spheroid, with axes in any proportion that we choose to try; then to calculate mathematically the length of the measure corresponding to the observed inclination to the vertical in different parts of the earth, and to find how nearly these calculated measures agree with the measured arcs; to ascertain whether they agree so nearly that there is no discordance beyond what can be fairly explained by the circumstances of the observations. They come to this: the proportion of the two axes of the earth is as 299 to 300: the shorter axis of 41,707,600 feet would pass through the Pole, and