FRO 
508 The rivers in Britain frozen for two 
months. 
558 The Danube quite frozen over. 
695 Thames frozen six weeks ; booths 
built on it. 
759 Frost from Oct. 1, till Feb. 26, 
760. 
827 Frost in England for nine weeks. 
859 Carriages used on the Adriatic Sea. 
908 Most rivers in England frozen two 
months. 
923 The Thames frozen 13 weeks. 
987 Frost lasted 120 days : began Dec. 
22 . 
998 The Thames frozen five weeks. 
1035 Severe frost on June 24 : the corn 
and fruits destroyed. 
1063 The Thames frozen 14 weeks. 
1076 Frost in England from Nov. till 
April. 
1114 Several wooden bridges carried 
away by ice. 
1205 Frost in England from Jan. 14, 
till March 22. 
1407 Frost that lasted 15 weeks. 
1434 From Nov. 24, till Feb. 10, Thames 
frozen down to Gravesend. 
1683 Frost for 13 weeks. 
1708-9 Severe frost for many weeks. 
1715 The same for many weeks. 
1739 One for nine weeks : began De- 
cember 24. 
1742 Severe frost for many weeks. 
1747 Severe frost in Russia. 
1751 Severe one in England. 
1760 The same in Germany. 
1776 The same in England. 
1788 The Thames frozen below bridge ; 
booths on it. 
1794 Hard frost of many weeks. Ther. 
at London, mostly at 20 below 0 
of Fahrenheit. 
Hoar frost, is the dew frozen or congealed 
early in cold mornings ; chiefly in autumn. 
Though many Cartesians will have it formed 
of a cloud ; and either congealed in the 
cloud, and so let fall ; or ready to be con- 
gealed as soon as it arrives at the earth. 
Hoar frost, M. Regius observes, consists 
of an assemblage of little parcels of ice 
crystals, which are of various figures, ac- 
cording to the different disposition of the 
vapours, when met and condensed by the 
cold. 
FROTH spit, or Cuckow spit, a name 
given to a white froth, or spume, very com- 
mon in the spring, and first months of the 
summer, on the leaves of certain plants, 
FRU 
particularly on those of the common white- 
field lychnis or catch-fly. See Cicada. 
FRUCTESCENTIA, in botany, com- 
prehends the precise time in which, after 
the fall of the flowers, the fruits arrive at 
maturity, and disperse their seeds. In 
general, plants which flower in spring, 
ripen their fruits in summer, as rye ; those 
which flower in summer, have their fruits 
ripe in autumn, as the vine ; the fruit of 
autumnal flowers ripens in winter, or the 
following spring, if kept in a stove, or 
otherwise defended from excessive frosts. 
The time in which plants ripen their fruit, 
combined with that in which they germinal e 
and unfold their leaves, gives the entire 
space or duration of their life, which, in 
the same species, is proportionably short 
or long, according to the greater or less 
intensity of heat of the climate, in which 
they are cultivated. In general, it appears, 
that if the heat is equal and uninterrupted, 
the time betwixt the germinating or sprout- 
ing and flowering of annual plants, is equal 
to the interval betwixt their flowering and 
the maturation of the fruits, or even the 
total destruction of the whole plant. In 
very hot climates, an annual plant general- 
ly lives as long before as after flowering. 
But in temperate climates, as France and 
England, plants which rise in spring and 
flower before the month of June, live a 
little longer before than after flowering; 
such as flower in summer, as barley and 
oats, which flower in June, live as long be- 
fore as after; while the latter plants, 
which do not rise till autumn, live longer 
after flowering than before. These ob- 
servations apply chiefly to herbaceous an- 
nuals. See Milne’s Bot. Diet. 
FRUSTUM, in mathematics, a part of 
some solid body separated from the rest. 
The frustum of a cone is the part that 
remains, when the top is cut off by a plane 
parallel to the base ; and is otherwise call- 
ed a truncated cone. The frustum of a 
pyramid is also what remains after the top 
is cut off by a plane parallel to its base. 
To find the solid content of the frustum of 
a cone, pyramid, &c. the base being of any 
figure whatever : add the areas of the two 
ends, and the mean proportional between 
them together, then j of that sum will be 
the mean area, or the area of an equal prism, 
of the same altitude with the frustum ; and 
consequently that mean area multiplied 
by the height of the frustum, will give the 
solid content for the product : 
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