Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/15

Rh observations and at present the general verdict appears to be one of non-proven. Observations by lunars at Godthaab (in west Greenland), in 1863 and 1882–3 appeared to show on the contrary a decrease of longitude of 2.6 seconds of time. In 1922, however, Lt.-Col. Jensen made a careful determination of the longitude by means of wireless signals from Nauen and observations of star transits with a 13.5 cm. theodolite and obtained a value nearly five seconds more than the mean of the previous determinations. He considered that this was a confirmation of the westward movement of Greenland. Colonel Sir Charles Close (“Geogr. Journal,” Vol. 63, p. 147, 1924), will not accept this on account of the unreliability of lunars. The observations by means of wireless are, of course, far more accurate, and another observation similar to that of Jensen, carried out say ten years hence, should enable a definite verdict to be obtained.

Professor Wegener also refers to the determinations of the difference of longitude between Greenwich and Cambridge, Massachusetts, by means of cable signals in 1872, 1892, and 1914. These show a minute apparent increase of .023 seconds. Such determinations, however, are subject from time to time to disturbing influences the true nature of which is uncertain and the effects of these are larger than the small variation in question. We shall, however, henceforth be in a far better position to determine whether any real changes occur. Every day the same wireless signals are received and recorded by both observatories (as well as by others on the two continents), and every clear night all the year round the time of transit of star after star is also observed. Observations for longitude are therefore now being carried out almost continuously and the effects of temporary abnormal conditions can therefore be eliminated, so that most