RAT 
all limits. Upon the rarefaction of the air 
is founded the method of measuring altitudes 
by the barometer ; in ail cases of which the 
rarity of the air is found to be inversely as 
the force that compresses it, or inversely as 
the weight of all the air above it at any 
place. 
The open air, in which we breathe, says 
Sir Isaac Newton, is 8 or 900 times lighter 
than water, and by consequence 8 or 900 
times rarer. And since the air is com- 
pressed by the weight of the incumbent 
atmosphere, and the density of the air is 
proportionable to the compressing force, 
it follows by computation, that at the height 
of about seven English miles from the 
earth, the air is four times rarer than at 
the surface of the earth ; and at the height 
of 14 miles, it is 16 times rarer than at the 
surface of the earth ; and at the height of 
§1, 28, or 35 miles, it is respectively 64, 
256, or 1024 times rarer, or thereabouts ; 
and at the height of 70, 140, and 210 miles, 
it is about 1,000,000, 1 , 000 , 000 , 000 , 000 , or 
1,000,000,000,000,000,000, &c. 
Mr. Cotes has found, from experiments 
made with a thermometer, that linseed-oil 
is rarified in the proportion of 40 to 39 in 
the heat of the human body; in that of 
to 15 to 14, in that degree of heat wherein 
water is made to boil ; in the proportion of 
15 to 13, in that degree of heat wherein 
melted tin begins to harden ; and finally, 
in the proportion of 23 to 20, in that de- 
gree wherein melted tin arrives at a per- 
fect solidity. The same author discovered, 
that the rarefaction of the air, in the same 
degree of heat, is ten times greater than 
that of the linseed-oil; and the rarefaction 
of the oil, about fifteen times greater than 
that of the spirit of wine. 
RASANT, or Razant, in fortification. 
Rasant-flank, or line, is that part of the 
curtain or flank whence the shot exploded 
rase, or glance, along the surface of the 
opposite bastion. 
RAT. See Mus. 
RATCH, or Rash, in clock-work, a sort 
of wheel having twelve fangs, which serve 
to lift up the detents every hour, and make 
the clock strike. 
RATCHETS, in a watch, are the small 
teeth at the bottom of the fusy, or barrel, 
which stops it in winding up. 
RATE, a standard or proportion, by 
which either the quantity or value of a 
thing is adjusted. 
Rate of a ship of war is its order, de- 
gree, or distinction, as to magnitude, bur- 
RAT 
den, &c. The rate is usually accounted 
by the length and breadth of the gun-deck, 
the number of tons, and the number of 
men and guns the vessel carries. Of these 
there are six rates. A first-rate man of 
war has its gun-deck from 159 to 174 feet 
in length, and from 44 to 50 feet broad ; 
it contains from 1313 to 1882 tons, has 
from 706 to 800 men, and carries from 
96 to 100 guns. Second rate ships have 
their gun-decks from 153 to 165 feet long, 
and from 41 to 46 feet broad ; they contain 
from 1086 to 1482 tons, and carry from 
524 to 640 men, and from 84 to 90 guns. 
Third rates have their gun-decks from 140 to 
158 feet in length, from 37 to 42 feet broad ; 
they contain from 871 to 1262 tons ; carry 
from 389 to 476 men, and from 64 to 80 
guns. Fourth rates are in length on the 
gun-decks from 118 to 146 feet, and from 
29 to 38 broad ; they contain from 448 to 
915 tons ; carry from 226 to 346 men, and 
from 48 to 60 guns. Fifth rates have their 
gun-decks from 100 to 1 20 feet long, and 
from 24 to 31 broad ; they contain from 
259 to 542 tons, and carry from 145 to 190 
men, and from 26 to 44 guns. Sixth rates 
have their gun-decks from 87 to 95 feet 
long, and from 22 to 25 feet broad ; they 
contain from 152 to 256 tons, carry from 
50 to 110 men, and from 16 to 24 guns. 
It is to be observed, that the new-built 
ships are much larger, as well as better, 
than the old ones of the same rate ; whence 
they double numbers all along ; the larger 
of which express the pioportions of the 
new-built ships, as the less those of the 
old ones. 
RATIO, in mathematics, is the rela- 
tion which one quantity bears to another 
in respect of magnitude, the comparison 
being made by considering how often one 
contains, or is contained by, the other. 
Thus, in comparing 6 with 3, we observe 
that it has a certain magnitude with respect 
to 3, winch it contains twice ; again, in 
comparing it with 2, we see that it has a 
different relative magnitude, for it contains 
2 three times, or it is greater when com- 
pared with 2 than it is when compared 
with 3. The ratio of « to 6 is usually 
expressed by two points placed between 
them, thus, a : 6 ; and the former is called 
the antecedent of the ratio, the latter the 
consequent. When one antecedent is the 
same multiple, part, or parts, of it’s con- 
sequent, that another antecedent is of its 
consequent, the ratios are equal. Thus, 
the ratio cff 4 : 6 is equal to the ratio of 
