Page:Book of record of the time capsule of cupaloy (New York World's fair, 1939).djvu/51



HE geodetic latitude and longitude of the Time Capsule has been determined by the United States Coast and Geodetic Survey by means of precise triangulation measurements from nearby stations of an extensive rigid Federal net comprising more than fifty thousand stations distributed over the United States. The net extends from the Atlantic to the Pacific Ocean, across the entire North American continent, and is included between latitudes 25° and 49° north of the Equator, and longitudes 68° and 125° west from Greenwich, England. The net has been extended into Canada and Mexico by the two countries involved & the datum on which it is based is called the North American Datum of 1927.

The accompanying sketch shows the first-order stations of the national net in the general vicinity of the Time Capsule. It should be noted that the latitude and longitude furnished for the Capsule are geodetic & may differ by as much as five seconds or more from the latitude and longitude determined by astronomical observations alone. This is due to deflections of the plumb line from the vertical, which are caused by the attraction of mountain masses or other topographic features & by the