MARINER’S 
each end of the lines which constitute the 
angle or upper part of the letter, are two 
pallets, not much unlike the figure of the 
log ; one of which falls in the same propor- 
tion as the other rises. The falling or 
pendant pallet meeting a resistance from 
the water, as the ship moves, has by that 
means a circular motion under water, which 
is faster or slower according as the vessel 
moves. This motion is communicated to a 
dial within the ship, by means of a rope 
fastened to the tail of the Y, and carried 
to the dial. The motion being thus com- 
municated to the dial, vvhich has a bell in 
it, it strikes exactly the number of paces, 
miles, &c. which the ship has run. Thus 
the ship’s distance is ascertained, and the 
forces of tides and currents may also be 
discovered by ' this instrument. See Phil, 
Trans. 
MARINER’S compass, is an instrument 
used at sea by mariners to direct and ascer- 
tain the course of their ships. , It consists 
of a circular brass box, which contains a pa- 
per card with the 32 points of the compass 
or winds, fixed on a magnetic needle tliat 
always turns to the north, excepting a small 
deviation, which is variable at diff'ereiit 
places, and at the same place at different 
times. The needle, with the card, turns 
on an upright pin fixed in the centre of the 
box. To the middle of the needle is fixed 
a brass conical socket or cap, by which the 
card hanging on the pin turns freely round 
the centre. The top of the box is covered 
with a glass, to prevent the wind from dis- 
turbing the motion of the card. The whole 
is inclosed in another box of wood, where 
it is suspended by brass hoops or gimbals, 
to keep the card in a horizontal position 
during the motions of the ship. The whole 
is to be so placed in the ship, that the mid- 
dle section of the box, parallel to its sides, 
may be parallel to the middle section of 
the ship along its keel. See Plate Miscel, 
fig. 9. 
The mariner’s compass was long very 
rude and imperfect, but at kngth received 
great improvement from the invention and 
’xperimeuts of Dr. Knight, who discovered 
ihe useful practice of making artificial mag- 
lets ; and the farther emendations of Mr. 
fraeaton, and Mr. M'Cullocli, by which 
tie needles are larger and stronger tlian 
ftrmerly, and instead of swinging in gim- 
COMPASS. 
bals, the compass is supported in its very 
centre upon a prop, and the centres of mo- 
tion, gravity, and magnetism are brought 
almost all to the same point. After the dis- 
covery of that most useful property of the 
magnet, or loadstone, viz. its giving a po- 
larity to hardened iron or steel, the com- 
pass was many years in use before it was 
known in anywise to deviate from the poles 
of the world. About the middle of the six- 
teenth century, so confident were some 
persons that tire needle invariably pointed 
due north, that they treated with contempt 
the notion of the variation, which about 
that time began to be suspected. How- 
ever, careful observations soon discovered, 
that in England and its neighbourhood, the 
needle pointed to the eastward of the true 
north line ; and the quantity of this devia- 
tion being known, mariners became as well 
satisfied as if tiie compass had none; be- 
cause the trud course could bo obtained by 
making allowance for the true variation. 
From succeeding observations it was af- 
terwards found, that the deviation of the 
needle from the north was not a constant 
quantity, but that it gradually diminished, 
and at last, namely about the year 1657, it 
was found that the needle pointed due 
north at London, and has ever since been 
going to the westward. 
The azimuth compass differs' from the 
common sea compass in tlsis , that the cir- 
cumference of the card or box is divided 
into degrees ; and there is fitted to the box 
an index with two sights, which are upright 
pieces of brass, placed diametrically oppo- 
site to each other, having a slit down the 
middle of them, through which the sun or 
star is to be viewed at the time of observa- 
tion. See Azimuth. 
The figure of the compass card, with the 
names of the 32 points or winds, are given 
Plate Miscel. fig. 10. As there are 32 
whole points quite around the circle, which 
contains 360 degrees, therefore each point 
of the compass contains the tliirty-second 
part of 360, that is. 111 degrees, or 11° 16'; 
consequently the half point is 5° 37' 30'', 
and the quarter point 2° 48' 45". 
The points of the compass are otherwise 
called rhumbs ; and the numbers of de- 
grees, minutes, and seconds, niade by every 
quarter point with the meridian, are exhi- 
bited in the following table. 
