Page:Popular Science Monthly Volume 30.djvu/257

 Rh uttered his historical "Eppur si muove," has been parallel to the advance made in all other branches of scientific knowledge and methods of investigation.

The first notions concerning the form of the earth were that its form was that of a tablet, ending abruptly at its extremities into what would be considered the abyss, which could not be reached by man. The idea that the earth was nothing but a plane was abandoned before the beginning of the Christian era. The earlier attempts at calculating the size of the globe were based on astronomical observations. It would be difficult to-day to say within what degree of accuracy the figures then obtained could have been relied upon, as the units of measurement used by those pioneers have been lost and could not be compared with the units now in use.

One of the earlier attempts at obtaining the actual length of the earth's meridian by direct measurement of a portion of the same was made in the sixteenth century by a French doctor. The means employed, although very ingenious, would be considered perfectly clumsy and inadequate by the modern scientist. There was in this early measurement no attempt at mathematical precision as understood in the present century, and, considering the simplicity of the method employed by the doctor, it is only to be wondered that no greater error was obtained in its final result. The measurement consisted simply in driving from Paris to Amiens, and counting the revolutions of the wheels of the carriage, and from the number of revolutions of the wheels obtain the distance between the two cities, which could serve as a basis for calculating the length of the meridian. Of course, this calculation could not by any means be considered accurate, but, taking into account the means employed, the result obtained has been subsequently found to be wonderfully precise. The most curious thing about it is, that what would now be considered grave errors and inexactitudes were so distributed that they almost compensated each other, and the dimensions then obtained show only slight differences with the dimensions given by the most recent measurements. Thus chance (and no better name could be found) permitted of the same results, with only a small final error, being obtained with that crude method, that are now obtained with the most precise instruments and with the most complicated calculations,

Geodetical triangulation is, like many of the other branches of scientific applications, essentially a child of the modern era. It is not older than the seventeenth century; the first application of geodetical triangulation to the measurement of an arc of the earth's meridian having been made in Holland at the beginning of that century. It was followed by similar measurements in England and in France, but in all these measurements the arc measured was never greater than two degrees, and the importance of such measurements on the question of the length of the earth's meridian could therefore not be