248 WRITINGS OF JOSEPH HENRY. [1855- 



only give a brief exposition of his nomenclature. He divides 

 clouds into three primary modifications: cumulus, stratus, 

 and cirrus, with intermediate forms passing into one another 

 under the names cumulo-stratus, cirro-stratus, cirro-cumulus; 

 and lastly, a composite form, resulting from a blending or 

 confusion of the others, under the name cirro-cumulo-stratus 

 or nimbus. 



1. Cirrus, consisting of parallel or diverging fibres, ex- 

 tended by increase of material in any or in all directions. 



2. Cumulus, convex or conical masses, increasing upward 

 from a horizontal base. 



3. Stratus, a widely extended continuous horizontal sheet. 



4. Cirro-cumulus, generally known as " mackerel sky," con- 

 sisting of small rounded masses, disposed with more or less 

 regularity and connection. 



5. Cirro-stratus, consisting of horizontal or slightly inclined 

 masses, undulating or separating into groups, giving the idea 

 of a shoal of fish in the distance. 



6. Cumulo-stratus consists of a blending of the cirro-stratus 

 with the cumulus. 



7. Nimbus is the cloud from which a continued rain falls. 

 A drawing of these different forms of clouds will be found 



in the instructions for meteorological observations published 

 by the Smithsonian Institution. 



Dew and hoar frost. — When a mass of moist air is brought 

 in contact with a cold body its vapor is condensed into water 

 and deposited in minute globules on the cooled surface, which 

 constitute dew. If the temperature of the surface is below 

 the freezing point the globules of water will be frozen into 

 minute crystals of ice, which constitute hoar frost. For a 

 long time the nature of these phenomena was entirely mis- 

 conceived ; the effect was put for the cause, the dew being 

 regarded as producing the chill which accompanies its for- 

 mation instead of the reverse. Dr. Wells of London, born in 

 South Carolina, was the first who gave the subject a scien- 

 tific investigation, and by a series of ingenious, accurate and 



