FRI 
hence, when the gale increases, it is said to 
freshen. In the plural, the word implies 
the impetuosity of an ebb-tide, increasing 
by heavy rains and flowing out into the 
sea, which it often discolours to a conside- 
rable distance from the shore, so that the 
line which divides the two colours, may be 
perceived distinctly for a great length along 
the coast. 
FRET, or Frette, in architecture, a 
kind of knot or ornament, consisting of two 
lists or small fillets, variously interlaced or 
interwoven, and running at parallel dis- 
tances equal to their breadth. 
Fret, in heraldry, a bearing composed of 
six bars, crossed, and variously interlaced. 
Fret, in music, signifies a kind of stop 
on some instruments, particularly bass- 
viols and lutes. Frets consist of strings 
tied round the neck of the instrument at 
certain distances, within which such and 
such notes are to be found. 
Fret work, that adorned with frets. It 
is sometimes used to fill up and enrich flat 
empty spaces, but is mostly practised in 
roofs, which are fretted over with plaster- 
work. The Italians also use fret-works in 
the mantling of chimneys, with great figures; 
a cheap piece of magnificence, and as dura- 
ble almost within doors, as harder matters 
in the weather. 
FRICTION, in mechanics, the rubbing 
of the parts of engines and machines against 
each other, by which means a great part 
of their effect is destroyed. 
It is hardly possible to lay down general 
rules concerning the quantity of friction, 
since it depends upon a multiplicity of cir- 
cumstances, as the structure, firmness, elas- 
ticity, &c. of the bodies rubbing against 
each other. Some authors make friction 
upon an horizontal plane, equal to one-third 
of the weight to be moved ; whilst others 
have found it to be considerably less. Two 
objects must, however, be observed, m. 
the loss of power which is occasioned by it, 
and the contrivances which have been made, 
and are in use, for the purpose of diminish- 
ing its effects. A body of an horizontal 
plane should be eapable of being moved by 
the application of the least force ; but this 
is not the case, and the principal causes 
which render a greater or less quantity of 
force necessary for it, are, 1, the roughness 
of the contiguous surfaces ; 2, the irregula- 
rity of the figure, which arises either from 
the imperfect workmanship, or from the 
pressure of one body from the other ; 3, an 
adhesion, or attraction, which is more or less 
VOL. III. 
FRI 
powerful according to the nature of the 
, bodies in question ; and 4, the interposi- 
tion of extraneous bodies, such as moisture, 
dust, &c. 
Innumerable experiments have been made 
for the purpose of determining the quantity 
of obstruction, or of friction, which is pro- 
duced in particular circumstances. But 
the results of apparently similar experi- 
ments, which have been made by different 
experimenters, do not agree ; nor is it likely 
they should, since the least difference of 
smoothness or polish, or of hardness, or iu 
short, of any of the various concurring cir- 
cumstances, produces a different result. 
Hence no certain and determinate rules can 
be laid down with respect to the subject of 
friction. Mr. Vince, who has done much 
on this subject, infers, 1, That friction is an 
uniformly retarding force in hard bodies, 
not subject to alteration by the velocity, 
except when the body is covered with cloth, 
woollen, &c. and in this case the friction 
increases a little with the velocity. 2, Fric- 
tion increases in a less ratio than the quan- 
tity of matter or weight of the body. This 
increase, however, is different for the diffe- 
rent bodies, more or less, nor is it yet suffi- 
ciently known for any one body, what pro- 
portion the increase of friction bears to the 
increase of weight. 3, The smallest surface 
has the least friction, the weight being the 
same. But the ratio of the friction to the 
surface is not yet accurately known. Mr. 
Vince’s experiments consisted in determin- 
ing how far the sliding bodies would be 
drawn in given times, by a weight hanging 
freely over a pulley. This method would 
both shew him if the friction was a constant 
retarding force, and the other conclusion* 
above stated. For as the spaces described 
by any constant force, in given times, are 
as the squares of the times, and as the 
weight drawing the body is a constant force, 
if the friction, which acts in opposition to 
the weight, should also be a constant force ; 
then their difference, or the force by which 
the body is urged, will also be constant, in 
which case the spaces described ought to 
be as the squares of the times, which hap- 
pened accordingly in the experiments. The 
friction, cceteris paribus, increases with the 
weight of the superincumbent body, and al- 
most in the same proportion. The friction, 
or obstruction which arises from the bend- 
ing of ropes about machines, is influenced 
by a variety of circumstances, such as their 
peculiar quality, the temperature of the at- 
mosphere, and the diameter, or curvature 
Q 
