1870.] The approaching Total Solar Eclipse. 479 



presented in Fig. 1, that there are two respects in which this 

 eclipse is unfavourable . First of all, the track of the shadow lies 

 far from the centre of the disc. It is clear that, pro tanto, the 

 shadow is rendered smaller by falling near the outer parts of 

 the disc ; because these parts lie farther than the centre from the 

 sun. Secondly, the elevation of the sun at the time of eclipse is 

 not considerable. Since the sun is vertical at the place which 

 occupies the centre of the earth's illuminated disc, and on the 

 horizon for any place which lies on the circumference of that disc, 

 it is obvious that when the track of the moon's shadow lies as in 

 Fig. 1, the sun's elevation is relatively small during total obscura- 

 tion. In the present eclipse, at the stations where the chief 

 observing parties will be placed, the sun's elevation will be about 

 30 degrees, amply sufficient for ordinary observing purposes, but 

 not altogether so great as might be desired for spectroscopic and 

 polariscopic researches, and still less satisfactory for photography. 



Fig. 2 presents on a larger scale the track of the moon's shadow, 

 and the actual oval shape of the black spot which seen foreshortened 

 in Fig. 1 appears as a circle. It will be seen that Odemira in 

 Portugal, Cadiz and Xeres in Spain, Oran and Eatna in Africa, and 

 Syracuse in Sicily, are the principal towns which lie very close to 

 the central line. But it is probable that the stations will be selected 

 without special reference to the proximity of towns ; indeed for many 

 purposes the less inhabited regions of a country are best suited for 

 such observations as have to be made during eclipse. 



Although Mount Etna is not very close to the central line, there 

 are reasons for believing that a party stationed on the summit of 

 this mountain would be enabled to make important observations. 

 They would be more than twice as far raised above the sea-level as 

 those observers were, who during the American eclipse obtained 

 such favourable views of the solar corona from the summit of 

 White Top Mountain. It will be remembered by our readers that 

 General Myer reports the extension of the corona as seen from this 

 station to have exceeded more than twofold the extension observed 

 by those at lower levels. As there will probably be an English 

 observing party near Syracuse, it would be a matter of the utmost 

 interest and importance to compare their observations of the corona 

 with those made at the summit of Etna. 



At present, it may be mentioned in passing, there seems every 

 reason to believe that two important expeditions will be sent from 

 England to observe the eclipse. As we write, the arrangements are 

 not complete, and there still remains a possibility that the whole 

 undertaking may fall through. But it is hoped that this may not 

 be the case, and that the large array of volunteers whose names 

 appear in the list of the two proposed expeditions may be enabled to 

 devote their energies to the work they have severally undertaken. 



