071 the Formation of Mists in particular Situations. 297 



fectlv clear, the appearance of mist above the river in the evening 

 Tiniformlv coincided with the diminution of the temperature of the 

 air from "three to six degrees beloio thatot the river, and the dis- 

 appearance of fog in the morning with the elevation of the tern- 

 pelature of the air above that of the nver. From Ratisbonne to 

 Passau,thetemperatureof theDancfl^evvas preuyunuorm through- 

 out the 24 hours, being highest, 62° F. or 62^ F., between 12 

 and 2 o'clock, and about one degree less before sun-nse, and the 

 temperature of the air from 61° F to 73" F. during the day and 

 from 61" to 54° F. during the night. Below Passau, the Inn and 

 the Hz flow into the Danube*. On examining the temperature 

 of these rivers at 6 o'clock A.M. June 11, that of the Danube 

 was found to be 62" F., that of the Inn 56f F., and that of the 

 Hz 56" F. • the temperature of the atmosphere on the banks 

 where their streams mixed, was 54". The whole surface of the 

 Danube was covered with a thick fog ; on the Inn there was a 

 slight mist, and on the Ilz barely a haziness indicating the de- 

 position of a very small quantity of water. About 100 yards be- 

 low the place where the three rivers joined, the temperature of 

 the central part of the Danube was 59° F., and here the quantity 

 of mist was less than on the bed of the Danube before the junc- 

 tion ; but about half a mile below, the warmer water had again 

 found its place at the surface, and the mist was as copious as before 

 the union of the three rivers. June 12th, the evening vvas cloudy, 

 and the temperature of the atmosphere remained till after dark 

 higher than that of the river, being, when the last observation 

 was made, 63° F. when there was not the slightest appearance of 

 mist Tlie skv was clearer before sun-nse on the i3th, and the 

 thermometer immediately after sun-rise, in the air above the river, 

 stood at 55^^ F. the temperature of the Danube being bl t . ; 

 a thin mist was seen immediately above the river; but there be- 

 ine no mass of vapour to exclude the sun-beams, it rapid.'y dis- 

 appeared, and was not visible a few feet from the surface; and 

 ill half an hour the whole atmosphere was perfectly transparent. 



In passing along the Rhine from Cologne to Coblentz, May 

 31st and June 2d and 3d, the nights being very clear, the same 

 phaenomenon of the formation of mists was observed, precisely 

 under the same circumstances ; but as I could examine the tem- 

 perature of the air and of the river only close to the banks, and 

 in two or three situations, my observations were less precise and 

 less numerous ; the mist formed later in the evening, and disap- 

 peared sooner in the morning, than on the Danube; which was 

 evidently owing to the circumstances of the atmosphere being 



•• • The Danube was greenish, the Inn h.ul a milky blueness the "z was 

 perfectly ,.cllucid ; but from the rapidity with wh.cb the Inn dfscend«d, its 

 water* at tUis »pot give their tint to the whole surface. warmer 



