FOG 
F 0 L 
755 
niy’s incursions, cover its own garrisons, and 
keep the enemy in continual alarm. 
Flying pinion, is part of- a clock, having 
a fly, or tan, whereby to gather air, and so 
bridle the rapidity of the clock’s motion, 
when the weight descends in the striking part. 
See Clockwork. 
FOCUS, in geometry and conic sections, 
is applied to certain points in the parabola, 
ellipsis, and hyperbola, where the rays re- 
flected from all parts of these curves concur 
and meet. 
FOCI of an ellipsis, are two points in the 
longest axis, on which as centres the ligure is 
described. If from the foci two right lines 
are drawn, meeting one another in the peri- 
phery of the ellipsis, their sum will be always 
equal to the longest axis ; and therefore when 
an ellipsis and its two axes are given, and 
the foci are required, you need only take 
half the longest axis in yonr compasses, and 
setting one loot in the, end of the shorter, the 
other foot will cut the longer in the focus 
required. 
Focus of an hyperbola, is that point in 
the axis, through which the latus rectum 
passes ; from whence if any two right lines 
are drawn meeting in either of the opposite 
hyperbolas, their difference will be equal to 
the principal axis. 
Focus of a parabola, a point in the axis 
within the figure, distant from the vertex one 
fourth pari of the latus rectum. 
Focus, in optics, is the point in which the 
fays are collected, after they have under- 
gone reflection or refraction. See Optics. 
FODDElt, in the civil law, is used for a 
prerogative that the prince has, to be pro- 
vided of corn and other meats for his horses, 
by the subjects, in his warlike expeditions. 
Fodder, or Fother, in mining, a mea- 
sure containing twenty-two hundred and a 
half weight, though in London but twenty 
hundredweight. 
FOETUS. See PhysiologW 
FOG, or Mist, a meteor, consisting of 
condensed vapours, floating near the surface 
of the earth. Mists, according to lord 
Bacon, are imperfect condensations of the 
air, consisting of a large proportion of the 
air, and a small one of the aqueous vapour : 
and these happen in the winter, about the 
change of the weather from frost to thaw, 
or from thaw to frost ; but in the summer 
and in the spring, from the expansion of the 
dew. If the vapours, which are raised plenti- 
fully from the earth and waters, either by the 
solar or subterraneous heat, do at their first 
entrance into the atmosphere meet with cold 
enough to condense them to a considerable de- 
gree, their specific gravity is by that means 
increased, and thus they will be stopped 
from ascending; and either return back in 
form of dew or of drizzling rain, or remain 
suspended some time in the form of a fog. 
Vapours may be seen on the high grounds as 
well as the low, but more especially about 
marshy places. They are easily dissipated 
by the wind, as also by the heat of the sun. 
They continue longest in the lowest grounds, 
because those places contain most moisture, 
and are least exposed to the action of the 
wind. Hence we may easily conceive, that 
fogs are only low clouds, or clouds in the 
lowest region of the air ; as clouds are no 
other than fogs raised on high. When fogs 
stink, then the vapours are mixed with 
1 putrid and offensive exhalations. 'Objects 
viewed through fogs appear larger mid more 
remote than through the common air. Mr. 
Boyle observes that, upon the coast of Coro- 
mandel, and most maritime parts of the East 
Indies, there are, notwithstanding the heat 
of the climate, annual fogs, so thick, as to oc- 
casion people of other nations who reside 
there, and even the more tender sort of the 
natives, to keep their houses close shut up. 
Fogs are commonly pretty strongly electri- 
fied, as appears from Mr. Cavallo’s experi- 
ments upon them. See Meteorology. 
FOIL, among glass-grinders, a sheet of 
tin, with quicksilver, &c. laid on the back- 
side of a looking-glass, to make it reflect. 
See Foliating of Looking-glasses. 
Foil, among jewellers, a thin leaf of metal 
placed under a precious stone, in order to 
increase its brilliancy, or give it an agreeable 
and different colour. These foils are made 
either of copper, gold, or gold and silver to- 
gether ; the copper foils are commonly 
known by the name of Nuremberg, or Ger- 
man foils; they are prepared as follows: 
Procure the thinnest copper-plates you can 
get ; beat these plates gently upon a well- 
polished anvil, with a polished hammer, as 
thin as possible ; and placing them between 
two iron plates as thin as writing-paper, heat 
them in the fire; then boil the foils, in a 
pipkin, with equal quantities of tartar and 
salt, constantly stirring them till by boiling 
they become white ; after which, taking them 
out, and drying them, give them another 
hammering till they are made fit for your 
purpose; however, care must be taken not 
to give the foils too much heat, for fear of 
melting, nor must they be too long boiled, 
for fear of attracting too much salt. 
The manner of polishing these foils is as 
follows: take a plate of the best copper, one 
foot long and about five or six inches wide, 
polished to the greatest perfection; bend this 
to a long convex, fasten it upon a half roll, 
and fix it to a bench or table ; then take 
some chalk, washed as clean as possible, and 
filtred through a fine linen-cloth, till it is 
as fine as you can make it ; and having laid 
some on the roll, and wetted the copper all 
over, lay your foils upon it, and with a polish- 
ing stone and the chalk, polish your foils till 
they are bright as a looking-glass; after 
which they must be dried, and laid up secure 
from dust. 
FOLD-net, among sportsmen, a sort of 
net with which small birds are taken in the 
night, of which there are two sorts; the least 
may be managed by one man only, but the 
greatest must be carried by two, and used 
thus: let the net be fixed on both sides to 
two strong, straight, and light poles about 
twelve feet long, each man holding one of 
them ; let there be one behind them, at the 
distance of two yards, to carry lights : the 
nets must be canned between the wind and 
the birds, which all naturally roost on their 
perches with their breasts against the wind ; in 
consequence of this, he that beats the bushes 
on the other side of the hedge, will drive 
them out that way towards the light. 
FOLDING of sheep. See Husbandry. 
FOLIAGE, in architecture, is used for the 
representations of such flowers, leaves, 
branches, rinds, &c. whether natural or arti- 
ficial, as are used for enrichments on capitals, 
friezes, pediments, &c. 
F O N 
FOLIATE, in the higher geometry, a 
name given by Mr. de Moivre to a curve of 
the second order, expressed by the equation 
x 3 -\-i/=;axi/ ; being a species of defective hy- 
perbolas with one asymptote, and consisting 
ot two infinite legs crossing one another, and 
forming a sort oi leaf. 
FOLIATING of looking-glasses, the 
spreading the plates over, after they are po- 
lished, with amalgam, in order to reflect the 
image. It is performed thus: a thin blotting 
paper is spread on the table, and sprinkled 
with line chalk; and then a fine lamina or 
leaf of tin, called foil, is laid over the paper ; 
upon this mercury is poured, which is 
to be distributed equally over the leaf with 
a hare’s foot, or cotton: over this is laid 
a clean paper, and over that the glass 
plate, which is pressed down with the 
right-hand, and the paper drawn gently 
out with the left : ( his being done, the plate 
is covered with a thicker paper, aad leaden 
with a greater weight, that the superfluous 
mercury may be driven out, and the tin 
adhere more closely to the glass. When it 
is dried, the weight is removed, and the 
looking-glass is complete. Some add an 
ounce of marcasite, melted by the fire ; and, 
lest the mercury should evaporate in smoke, 
pour it into cold water ; and when cooled, 
squeeze it through a cloth or through leather. 
Some add a quarter of an ounce of tin and 
lead to the marcasite, that the glass may dry 
the sooner. 
Foliatin g of globe looking-glasses, is 
done as follows : Take five ounces of quick- 
silver, and one ounce of bismuth ; of lead 
and tin half an ounce each: first put the lead 
and tin into fusion, then put in the bismuth, 
and when you perceive that in fusion too, 
let it stand till it is almost cold, and pour the 
quicksilver into it; after this, take the glass 
globe, which must be very clean, and the 
inside free from dust; make a paper funnel, 
which put into the hole ot the globe, as near 
to the glass as you can, so that the amalgam 
when you pour it in, may not splash, and 
cause tne glass to be. full of spots; pour it in 
gently, and move it about, so that the a- 
malgam may touch every where. If you 
find the amalgam begin to get curdly and 
fixed, then hold it over a gentle fire, and it 
will easily flow again. And if you find the 
amalgam too thin, add a little more lead, tin, 
and bismuth to it. The finer and clearer 
your globe is, the better will the looking- 
glass be. 
FOLKMOTE, or Folcmote, according 
to Kennet, was the common-council of all 
the inhabitants of a city, town, or borough ; 
though Spelman will have the folkmote to 
have been a sort of annual parliament or con- 
vention of the bishops, thanes, aldermen, 
and freemen, on every May-day. Dr. 
Brady, on the contrary, tells us, that it was 
an inferior court, held before the king’s reeve, 
or his steward, every month, to do folk ridit 
FOMAHAUT, in astronomy, a star of the 
first magnitude, in the constellation Aqua- 
rius. See Astronomy. 
FOMENTATION, in medicine, the bath- 
ing any part of the body with a warm liquor. 
FONTEV RAUD, or order of Fontevraud, 
a religious order instituted about the latter 
part of the 11th century. By the rules of 
this order the nuns were to keep silence for 
ever, and their faces to be always covered 
