Page:In the high heavens.djvu/88

 astronomical conditions were favourable also turned out to be those where the geographical conditions were suitable and comparatively convenient. At Chili, in Argentina, in Brazil, and on the African coast, astronomers were able to obtain a series of admirable pictures, not often paralleled in eclipse observations. One special advantage offered by this chain of observing stations should be particularly noticed. It is a question of considerable importance to examine the nature of the changes which take place in the corona. It has sometimes been thought that such changes frequently occur with extreme rapidity. No doubt, when we remember the scale of the objects involved, it will hardly be imagined that in the brief interval of four or five minutes, during which the eclipse lasted, any variation in the corona should have taken place considerable enough to be recognised from the distance at which we are placed. We thus have the opportunity of carefully examining whatever changes may have taken place in the corona in the interval between the time of totality in Chili and the time of totality in Africa. As we have pointed out, this period is no less than two and a half hours. In this respect, the advantage offered by the eclipse of 1893 is almost unique, for though on other occasions observations of totality may have been possible for a number of seconds greater than those at either of the stations we have named, yet the circumstance of having in the same eclipse two occupied stations so widely separated as the western coast of North Africa and the western coast of South America is quite an exceptional advantage.

And now as to the problems which astronomers have proposed to themselves to solve when undertaking the