4 
Improvement in Field Surveying. , 37 
fourths of an inch in diameter, and from one anda half to two inch- 
es in circumference, and from this size down to that of .a small buk 
let. Some were united by a narrow neck, as shown by Fig. 1. 
Some were irregular and ragged on their edges, and crossed by 
irregular fractures, as is seen in Fig. 2. Others again, were dotted, 
with several air cells around the center one, as exhibited in Fig. 3. 
The center of each represents the air cells. 
These hail storms are sometimes accompanied by violent winds. 
_. They make their approach from every point of the compass save 
directly from the east, and they come most frequently from the south- 
west or north west. A person who has once closely observed them, 
can generally foretell their approach, from the appearance of the 
rising cloud. It uniformly exhibits a sea green color, and often seems 
much agitated, and small fragments of clouds often linger beneath 
the main body, or seem to be suddenly formed and to fly in pursuit of 
it. They occur when currents of air in the heavens, retain their winter . 
coldness, and intercept the drops of rain and convert them into hail- 
stones. This operation is not a little aided also, by the sudden dis- 
charges of the electric fluid of the clouds... In the south of France, 
they are very frequent and often destroy extensive vineyards. The 
believe so fully in the idea that the discharges of electricity 
influence their production, that they erect lightning rods by means 
of poles in their fields to lessen their occurrence and effects. In 
this case, the discharge of the fluid is gradual; and unattended by 
hail, at least in proportion to what would be the case, if let off in- 
heavy discharges. 
Augusta, Geo. June 18th, 1832. 
Arr. VII.—Improvement in Field Surveying. - eg 
Tue genefal principle or method of computing the areas of irreg~ 
ular plane figures, as described in Art. III, No. 45 of the Journal of 
Science, was introduced by E. F.. Johnson, Esq. into the course of 
instruction in the practical mathematics, in the institution of Capt. 
Partridge, in the year 1824, and the method is now extensively prac- 
ticed by many of the young men graduates of that institution, in 
various parts of the country. 
