METEOROLOGY. 417 



reasoning, tbat tlie carbon dust from prairie and forest fires and the smoke 

 of coal fires in cities have a strong affinity for aqueous vapor, which is at- 

 tracted and held in a little atmosphere aronnd each carbon particle, just 

 as hydrogen is attracted to spongy platinum. These little balloons of 

 vapor with dust centers, as they rise in the air, cool, both by radiation 

 and expansion, more rapidly than the surrounding air, and soon pass 

 from dry yellow haze (as in Indian-summer weather) into fog and rain. 

 Other kinds of dust particles probably produce the same effect, but in a 

 different manner, i. e., they simply cool more rapidly by radiation and 

 condense upon themselves as dew some of the neighboring aqueous vapor; 

 then becoming heavier, they grow by accretion of other dew-laden parti- 

 cles as they descend to the earth. — C. A.] 



Mr. I^ewth showed to the London Physical Society some experiments 

 illustrative of the fact announced by Mr. Mascart in 1875 that solid 

 particles in the air are necessary to the formation of fogs ; and, sec- 

 ondly, that certain gases, such as sulphurous-acid gas, also cause fogs 

 in the same way by permitting the moisture to condense upon these par- 

 ticles. The experiments consisted in passing an electric-light beam 

 through large bulbs of glass containing air and a small quantity of 

 water. When the air in the bulbs was washed with the water, and 

 thus freed from motes, the fog produced in the bulb by slightlj' exhaust- 

 ing it with an air-pump was much less than when the air of the room, 

 or smoke, or sulphurous- acid gas, was admitted into the bulb. The 

 dust on a platinum wire, rendered incandescent within the globe by an 

 electric current, also caused a sensible fog. It follows that with gas 

 fires instead of coal there would still be fogs, though not so black ones. 

 (^Nature, xxv, p. 475.) 



Prof. O. Keynolds has been deeply engaged in the study of the phe- 

 nomena of the surface tension of water; these bear upon the subject of 

 rain-drops, the union of floating particles of fog into larger drops, and 

 the floating of rain-drops on the clean water of i)onds. {Nature, xxv, 

 p. 23.) 



Prof. J. Elliot, of India, has investigated the rain-fall of Cherrapunji, 

 in the southwest of Assam, and on a small i^lateau forming the summit 

 of one of the spurs of the Khasia Hills. The rain-fall recorded at this 

 station averages 493 inches per annum, or while the normal wind-fall in 

 the neighboring plains is about 100 inches, he finds that this remark- 

 able rainfall, by far the largest known anywhere on the earth, is sim- 

 ply and solely owing to the presence of a vast mechanical obstruction, 

 namely, the precipitous hill on which the station stands, rising sud- 

 denly 4,000 feet, and whose resistance converts the horizontal motion 

 of the air into a vertical motion ; the ascending air cools rapidly by rea- 

 son of its expansion and condenses its moisture into deluges of rain. 

 {Natttre, xxv, p. 259.) 



Mr. Maxwell Hall has published in the Government Hand-Eook to 

 Jamaica the best resume as yet given of the climate and meteorology 

 H. Mis. 20 27 



