PROGRESS OF METEOROLOGY IN 1889. 235 



VI.— ATMOSPHERIC MOISTURE; CONDENSATION, FOGS, HAZE, AND 

 CLOUDS; RAIN, SNOW, HAIL, AND FLOOD. 



Amount of wafer in cloud. — Dr. J. Hanu has put together the obser- 

 vatious on the amount of moisture contained in a given volume of cloud 

 at different temperatures. In the experiments made by A. and 11. 

 Schlaginweit in 1851, the amount of moisture in the water particles in a 

 cloud was in every case less than the uncondensed vapor in the same 

 volume. {Meteorologische Zeitschriff, vi, p. 304.) 



London fog. — In an address on the relation of smoke to fogs in Lon- 

 don, Mr. F. A. E. Eussell shows that the characteristic London fogs 

 are produced by the mechanical combination of particles of water with 

 particles of coal or soot. The conditions of their development are a still 

 air, lower temperature near the ground than at a height of some hun- 

 dreds of feet, high relative humidity, a cloudless sky, and free radiation 

 into space. 



The darkness and peculiar coloring occur with greatest effect when a 

 very large quantity of coal is being burnt in domestic fires, hence 8 to 

 10 A. M. of the winter season is the time of thickest and darkest fogs. 

 The fogs are formed by the mixture of soot and smoke with an 

 already existing white fog. A thick layer of these carbonaceous par- 

 ticles prevents the sunshine from reaching and evaporating the particles 

 of natural fog. Thus the fog is blackened and its dissipation is retarded. 

 The author estimates that the loss from all sources due to this wasteful 

 method of burning coal is for London alone about £5,000,000 a year, 

 {Nature, xxxix, p. 34.) 



Raze. — Mr. Russell has made an elaborate analysis of the causes and 

 character of haze, of which the following is a partial summary: 



Unlike fog, haze commonly occurs when the lower air is in a state of 

 unusual dryness. Haze does not prevail on the Continent of Europe or 

 in the interior of North America to anything like the same extent as in 

 England. On the east coast of Scotland, and over all north Britain, 

 it is exceedingly common, especially in the spring, and during the prev- 

 alence of east wind. The conditions favorable for the production of 

 haze are : (1) A gentle wind from east-southeast to northeast, inclusive, 

 and east wind in general, especially with dry weather in spring and 

 summer. If the east wind be established up to a great height, the 

 lower air is usually clear, but if the upper current is from a westerly 

 direction, haze prevails, (2) Fine settled weather, with variable cur- 

 rents, a dry air, and little dew. (3) Opposition of currents — such as 

 occurs when several shallow barometric depressions exist over the coun- 

 try — and the atmospheric state preceding thunder-storms. (4) Damp 

 weather, with light winds and varying temperature. 



The very condition to which haze in England is commonly, and in a 

 certain sense correctly, attril)nt<'d — namely, atmospheric humidity — is. 



