CLOUDS. 408 
A glance at the skeleton-charts daily prepared to show the meteorological 
phenomena more readily to the eye, shows the magnificent extent of the atmos- 
pheric distances that then follow each other with such rapidity over the country. 
The several lines of equal barometic pressure seldom inclose a space within the 
region covered by the stations. aS ct es 
These lines are mostly in the form of curves of very great radius.  * ** 
Such far-spreading phenomena can surely not be produced by any local changes of 
temperature.” *K *K *K 
These extracts are teresting as showing the first steps taken by the Signal 
Service in the discussion of weather reports, the preparation of charts and the 
issue of forecasts. 
They also furnish valuable data in reference to the question of priority among 
the numerous applicants for the honor of originating the present system of weather 
work of the Signal Service. 
On January 1, 1874, in pursuance of an arrangement between Professor 
Henry and the Chief Signal Officer, the very extensive system of meteorological 
reports made by volunteer observers throughout the United States, under the su- 
pervision of the Smithsonian Institute, was transferred to the charge of the Signal 
Office. 
On June 19, 1874, the series of meteorological observations made at military 
posts and stations throughout the United States, were transferred to the Signal 
Office by the Surgeon General of the Army, thus concentrating the official mete- 
orological work of the country in one office and under one management, where it 
has since remained. 
CLOUDS. 
PROF. S. A. MAXWELL, MORRISON, ILL. 
__ Clouds are masses of aqueous vapor condensed to such an extent by a dimi- 
hution of temperature as to become visible. A given quantity of air will remain 
Wansparent so long as it is capable of absorbing watery vapor, and when it can 
absorb no more, it is said to be saturated. Even in this condition it 
is quite 
Jansparent; butif from any cause the temperature is lowered, a portion of the 
moisture is condensed, forming minute, though visible, vesicles of vapor, such as 
wre seen floating in the air during a fog. These vesicles are hollow spherules 
sufficiently opaque to render the clouds which they form able to exclude 
eg 
the sun’s 
Sy 5 5 
jays either wholly or in part. The temperature of a saturated portion of air may 
de diminished in two ways—a cold current of air may enter it, or it may itself rise 
ito a higher and colder stratum. The result of either of these conditions is 
sually the formation of clouds; and all or nearly all precipitation is due to the 
ooling of ascending currents at a vast height. 
i 
Ms 
