282 THE MECHANICS OF THE EAETH'S ATMOSPHERE. 



which was fouud even in the highest layer of fog raises some doubt in 

 this direction. Some observations made by First Lieutenant Moedebeck 

 aud Lieutenant Gross on the occasion of a balloon voyage made on 

 June 19, 1889, and which Lieutenant Gross has recently published * in a 

 very interesting essay, apparently speak more clearly on this point, 

 and certainly deserve a thorough scientific analysis, f 



Here also the passage through thick clouds showed that the temper- 

 ature at the upper boundary of these fell very low but immediately 

 above this it rose at once suddenly. The observations of humidity also 

 agree better with the theoretical views developed above. On this point 

 Lieutenant Gross says with reference to a diagram given by him which 

 shows the changes of the dry and wet thermometers, " We see from the 

 •comparison of the carves of the dry and wet thermometers that the 

 moisture of the air rapidly increases with approach to the cloud, and 

 that in the cloud itself where both curves coincide the air is completely 

 saturated with aqueous vapor. But it is only in the lower part of the 

 cloud that this is the case, and the moisture diminishes towards its 

 upper part, an observation that I have already frequently made. This 

 is certainly also explicable: In the upper part of the cloud the sun acts 

 again as at first. Immediately above the cloud the wet thermometer 

 makes a sudden rise. The air becomes suddenly very dry, as results 

 without anything further, from the heat reflected back from the cloud." 



That the lowest temperature should be observed immediately under 

 the upper boundary of the cloud in spite of the influence of the sun 

 seems to me explicable only by means of the cold due to evaporation 

 in accordance with the mauner above theoretically predicted. 



One ought to be able to observe with all sharpness on the Eiffel 

 tower the questions relating to the behavior of the upper surface of 

 fog since it must frequently happen there that the boundary floats but 

 a short distance above the meteorological instruments. 



Perhaps also it will be possible there to establish at different heights 

 self registering thermometers and psychrometers or hygrometers in 

 order to obtain truly simultaneous observations immediately above aud 

 below the upper boundary of the fog (or mist). 



((h) THE FORMATION AND DISSOLUTION OF FOG AND CLOUD. 



The preceding investigations into the formation of precipitation by 

 mixture of quantities of air of unequal warmth and moisture show that 



* Zeitschrift fur Luftschiff fahrt, 1889, vm, p. 249. 



t In referring to this essay I might also mention that Lieutenant Gross has also in 

 the meantime confirmed the expectation expressed in my former communication [see 

 pages 251-953] according to which the inversion of temperature in the region of the 

 winter anti-cyclone is not a peculiarity of mouutainous regions. On the occasion of 

 a balloon voyage undertaken on December 19, 18t8, from Berlin under the influence 

 <>t such an anti-cyclone, the sling thermometer gave an increase of temperature of 

 fi in 1,000 metres of ascent between Ip.ji, and 4 p. m. 



