466 Intelligence and Miscellaneous Articles. 



the electric light they look to a certain extent like flames. If 

 the point is brought a little nearer the water the vapour dis- 

 appears completely, although the water commences to boil briskly. 

 — Archives cles Sciences physiques et naturelles, April 1888. 



ON SOME PHENOMENA OF MIRAGE. BY J. L. SORET. 



In travelling by the steamer from Geneva to Evian, between 

 twenty-five minutes past one and twenty minutes to four, on 

 June 4, a very hot day, on which the temperature of the air must 

 have been considerably higher than that of the lake, M. Soret 

 observed the ordinary variations of refraction in these circum- 

 stances (fata morgana). The banks, which were really low, appeared 

 as if they terminated in raised beaches ; but the phenomenon varied 

 greatly every minute. M. Soret observed also for a few minutes 

 a mirage, described by M. Ch. Dufour (Bulletin de la Soc. Vaudoise des 

 Sc. Nat. 1854, vol. iv. p. 129), between Tvoire and Thonon: look- 

 ing at a sailing-boat coming near this latter place, the higher sails 

 are seen very white and shining; the lower sails appeared out of 

 shape, elongated vertically, dark, and looking like two confused 

 superposed images. 



But the appearance which most struck M. Soret was the follow- 

 ing, as he believes it has not yet been observed : — Between Tvoire 

 and Thonon was seen, on the side of the gulf of Anthy, an ap- 

 pearance as of white vapours, the puffs of which were superposed, 

 and were transported to the south-west by the wind. These tongues 

 of vapour, changing every instant, stood out quite bright on a dark 

 ground. The phenomenon lasted rather a long time. M. Soret 

 thinks it due to the variable state of the layers of air, which in 

 certain places presented conditions favourable for the production of 

 mirage, and gave a partial and dark image of the coast between 

 Tvoire and Anthy ; further, when the disturbance of the refraction 

 was less pronounced the image of the coast was not produced, and 

 these places appearing white had the appearance of vapours. 

 Speaking generally, the phenomenon should be manifested when 

 we are at the limit at which mirage is produced, and at the same 

 time when the layers of air are not stable. 



A fact of some importance is that, at certain moments and for 

 certain favourable positions, a lower and reversed image is seen of 

 objects situate near the surface of the water as during the ordinary 

 mirage, but with less permanency. 



On the following days M. Soret often observed the ordinary mirage 

 even when, at any rate on some of those days, the temperature was 

 but little higher than that of the water. Other observers, M. Forel 

 in particular, have sometimes observed the same fact. It is possibly 

 connected with the hygrometric state of the air. — Archives des 

 Sciences physiques et naturelles, September 1888. 



