Page:Popular Astronomy - Airy - 1881.djvu/271

Rh to every particle of the earth's structure,) then by the fundamental law of gravitation, the attraction of a mountain would be a sensible thing; for a mountain is a part of the earth, with this difference only, that though the mountain is small in comparison with the earth, yet you get so close to the mountain, that its effect may be very sensible as compared with the effect produced by the rest of the earth. Some parts of the earth are 8,000 miles from us, and their attraction will be comparatively small. It was therefore thought worth while to ascertain whether the attraction of a mountain would be sensibly felt; and the Schehallien observations were a noble experiment towards the attainment of that result.

The Schehallien Mountain ranges east and west; it was possible to make astronomical observations on the north and south sides; and it was also possible to connect the two places of observation by triangulation. Supposing Figure 63 to represent a section



of the mountain north and south, N the northern, S the southern observing station. Observations were made at N and S upon stars with the Zenith Sector;