84 The Astronomer Royal on the 



The only theory which has been formally propounded as 

 explaining them is that of M. Faye, who conceives them to 

 be the result of a kind of mirage. 



The Lecturer explained the nature of ordinary mirage (the 

 kind of reflection produced by the hot air adhering to a heated 

 surface of any solid) and described the distortion produced 

 in the image of a star as seen in the Northumberland tele- 

 scope of the Cambridge Observatory, when first mounted in a 

 square pyramidal tube, whose angles were constructed more 

 solidly than its sides, reducing the inner form to an octagon. 

 When this tube had become warm before observation in the 

 open air, the angle-blocks remained warm after the sides and 

 the internal air had become cool, and a kind of mirage was 

 produced which distorted the image of a star into four long 

 rays like the sails of a windmill. M. Faye has particularly 

 adverted to this instance, and conceived that in the circum- 

 stances of our atmosphere at the time of the eclipse, where 

 the air on one side only of the path of light is somewhat 

 heated by the sun, sufficient explanation might be found for 

 the distortion of some inequalities of the moon. The Lecturer 

 professed himself totally unable to follow this theory into 

 details, remarking only that in the rapid passage of the 

 moon's shadow he conceived it impossible to find air in the 

 state required for the explanation. 



The Lecturer then adverted to that part of his subject of 

 which all that had been already said was only introductory, 

 namely the approaching eclipse of July 28. After quoting 

 an American newspaper, shewing the great interest excited 

 by this eclipse beyond the Atlantic as one of the strongest 

 inducements for Americans to visit Europe in the coming 

 summer, he invited attention to its course across Europe. 

 Entering Norway near Bergen, the shadow crosses both coasts 

 of Norway, both coasts of Sweden, and the eastern coast of 

 the Baltic : then ranges through Poland and the south frontier 

 of Russia across the sea of Azof through Georgia to the 

 Caspian Sea. It passes Christiania, Goteborg, Carlscrona, 

 Danzig, Konigsberg, Warsaw, and Tiflis. A great part of 

 this course, especially that from Bergen to Konigsberg, is 

 very accessible by sea, and Warsaw by land. The Lecturer 



