EXP 
mates the flying-fishes spring out of the water 
by hundreds, to escape the rapacity of the 
dolphins, sharks, & c. When in the air, they 
have many formidable enemies to encounter 
within that element, viz. the pelican, eagle, 
diomeda, &c. and frequently throw them- 
selves on board the ships to escape their pur- 
suit. Their flesh is said to supply a palatable 
and nourishing food. There are two spe- 
cies. 
EX OFFICIO, among lawyers, signifies 
the power a person has, by virtue of his office, 
to do certain acts without being applied to. 
Thu's a justice of peace may ex officio at his 
discretion, take surety of the peace, without 
complaint made by any person whatsoever. 
There was formerly an oath ex officio, where- 
by a supposed offender was compelled in 
the ecclesiastical court to confess, accuse, or 
clear himself of a crime ; but this law is re- 
pealed. 
EXOMPHALUS, in surgery, called also 
omphalocele, and hernia umbilicalis, is a pre- 
ternatural tumor of the abdomen at the navel 
from a rupture, or distension of the parts 
which invest that cavity. See Surgery. 
EXORCISM, among the ecclesiastical 
writers, the expelling devils from persons 
possessed, by means of conjurations and 
prayers. 
EXORCISTS, in church-history, an order 
of men, in the antient church, whose em- 
ployment it w r as to exorcise or cast out de- 
vils. See the preceding article. 
EXORDIL M, in rhetoric, is the preamble 
or beginning, serving to prepare the audience 
for the rest of the discourse. 
EXO L1C, an appellation denoting a thing 
to be the produce of foreign countries. Ex- 
otic plants of the hot climates are very nu- 
merous, and require the utmost attention of 
the gardener to make them thrive with us. 
EXPANSION, as generally employed in 
science, denotes an increase of the bulk of 
any body by a power acting from within. ’ 
It may be laid down as a general rule, to 
which there is no known exception, that 
every addition or abstraction of caloric makes 
a corresponding change in the bulk of the 
body w hich has been subjected to this altera- 
tion in the quantity of its heat. In general, 
the addition of heat increases the bulk of a 
body, and the abstraction of it diminishes its 
bulk; but this is not uniformly the case, 
though the exceptions are not numerous. In- 
deed these exceptions are not only Confined 
to a very small number of bodies, but even in 
them they do not hold, except at certain 
particular temperatures, while at all other 
temperatures these bodies are increased in 
bulk when heated, and diminished in bulk 
by being cooled. We may therefore con- 
sider expansion as one of the most general 
effects of heat. It is certainly one of the 
most important, as it has furnished us with 
the means of measuring all the others. 
Though all bodies are expanded by heat 
and contracted by cold, and this expansion in 
the same body is always proportional to some 
function of the quantity of caloric added or 
abstracted ; yet the absolute expansion, or 
contraction, has been found to differ exceed- 
ingly in different bodies. In general, the 
expansion of gaseous bodies is greatest of all ; 
that of liquids is much smaller, and that of 
solids the smallest of all. Thus, 100 cubic 
inches of atmospheric air, by being heated 
EXP 
from the temperature of 32° to that of 2 12®, I 
are increased to 137.5 cubic inches; while 
the same augmentation of temperature only 
makes 100 cubic inches of water assume the 
bulk of 104.5 cubic inches.; and 100 cubic 
inches of iron, when heated from 32° to 2 i2°, 
assume a bulk scarcely exceeding *100.1 
cubic inches. From this example, we see 
that the expansion of air is more than eight 
times greater than that of water, and the ex- 
pansion of water about 45 times greater than 
that of iron. 
An accurate knowledge of the expansion 
of gaseous bodies being frequently of great 
importance in chemical researches, many 
experiments have been made to ascertain it ; 
yet, till lately, the problem was unsolved. 
The results of philosophers were so various 
and discordant, that it was impossible to form 
any opinion on the subject. This was owing 
to the want of sufficient care in excluding 
water from the vessels in which the expansion 
of the gases was measured. The heat which 
was applied converted portions of this water 
into vapour, which, mixing with the gas, to- 
tally disguised the real changes in bulk which 
it had undergone. To this circumstance we 
are to ascribe the difference in the determi- 
nations of de Luc, general Roy, Saussure, 
d’ivernois, &c. Fortunately the problem 
has lately engaged the attention of' Mr. Dal- 
ton of Manchester, and M. Gay Lussac; 
and their experiments, made with the proper 
precautions, have solved the problem. Mr. 
Dalton’s experiments are distinguished by a 
simplicity of apparatus which adds greatly to 
their value, as it puts it in the power of others 
to repeat them without difficulty. It con- 
sists merely of a glass tube, open at one end, 
and divided into equal parts; the gas to be 
examined was introduced into it after being 
properly dried, and the tube is filled with 
mercury at the open end to a given point ; 
heat is then applied, and the dilatation is ob- 
served by the quantity of mercury which is 
! pushed out. M. Gay Lussac’s apparatus 
is more complicated, but equally precise; 
and as his experiments were made on larger 
bulks of air, their coincidence with those of 
Mr. Dalton adds considerably to the confi- 
dence which may be placed in the results. 
From tire experiments of these philoso- 
phers it follows, that all gaseous bodies what- 
ever undergo the same expansion by the 
same addition of heat, supposing them placed 
in the same circumstances, it is sufficient 
then to ascertain the law of expansion ob- 
served by any one gaseous body, in order to 
know the exact rate of dilatation of them all. 
Now, from the experiments of Gay Lussac 
we learn, that air, by being heated from 32° 
to 2 12°, expands from 100 to 137.5 parts; the 
increase of bulk for 180° is then 37.5 parts; 
or, supposing the bulk at 32° to be unity, the 
increase is equal to 0.375 parts; this gives us 
0.00208, or _|^th part, for the expansion of 
air for 1° pf the thermometer. Mr. Dalton 
found, that 100 parts of air, by being heated 
from 55° to 212°, expanded to 132.5 parts; 
this gives us an expansion of 0.00207, or 
part, for 1°; which differs as little from 
the determination of Lussac as can be ex- 
pected in experiments of such delicacy. 
From the experiments of Mr. Dalton, it 
appears that the expansion of air is almost 
perfectly equable; that is to say, that the 
EXP 67Q 
same increase of bulk takes place by the 
same addition of caloric at all different tem- 
peratures. It is true, indeed, that the rate 
of diminution appears to diminish as the 
temperature increases'. Thus the expansion 
from 55° to 133:|°, or for the first 77 \ degrees, 
was 1 07 parts; while the expansion from 
133-2 to 212°, or for the next 77 p -§, was only 
158 parts, or 9 parts lt?ss than the first. But 
this difference, in all likelihood, is chiefly ap- 
parent; for de Luc has demonstrated that the 
thermometer is not an accurate measure of 
the increase of heat. 
From the experiments of Gay Lussac, it 
appears that the steam of water, and the va- 
pour of ether, undergo the same dilatation 
with air when the same addition is made to 
their temperature. We may conclude then 
that ail elastic fluids expand equally and uni- 
formly by heat; and that this expansion is 
nearly equable, though not perfectly so. 
The following table gives us the bulk ot a 
given quantity of air at all temperatures from 
32° to 2.12°. 
T em. 
Bulk. | 
Tern. 
Bulk. 
Tern. 
Bulk. 
32° 
100000* 
59 c 
105616 
86° 
111232 
33 
1 00208 
60 
105824 
87 
111440 
34 
100416; 
6l 
106032 
88 
111648 
35 
100624! 
62 
1 06240 
89 
111856 
36 
100832] 
63 
106448 
90 
1 12064 
37 
101040 
64 
106656 
91 
112272 
38 
101248] 
65 
106864 
92 
112486 
39 
101456] 
66 
107070 
93 
112688 
44 
1 0 1 664 
67 
107280 
94 
112896 
41 
101872 
68 
107488 
95 
1 13104 
42' 
102080 
69 
107696 
96 
1 13312 
43 
102238 
70 
107904 
97 
1 '35 >0 
44 
1 02496 
71 
108112 
98 
113728 
45 
102764 
72 
108320 
99 
1 13956 
46 
102912 
73 
108528 
100 
1 14144 
4 7 
103120 
74 
108736 
1 10 
1 16224 
4S 
1 03328 
75 
108944 
120 
1 18304 
49 
1 03536 
76 
1 09 1 52 
130 
1 5203 8 -4 
50 
103744 
77 
1 09360 
140 
122464 
51 
103952 
78 
109568 
150 
144544 
52 
104160 
79 
109776 
1 60 
126624 
63 
1.04268 
80 
109984 
170 
128704 
54 
104576 
81 
110192 
180 
130784 
55 
104784 
82 
110400 
190 
132864 
56 
104992 
83 
1 1060S 
200 
134944 
57 
105220 
84 
110816 
210 
137024 
58 
105408 
85 
111024 
212 
137440 
The expansion of liquid bodies differs from 
that of the elastic fluids, not only in quantity,, 
but in the want of uniformity with which 
they expand when equal additions are made 
to the temperature of each. This difference 
seems to depend, upon the fixity or volatility 
of the component parts of the liquid bodies ; 
for in general those liquids expand most by a 
given addition of heat, whose boiling tempe- 
ratures are lowest, or which contain in them 
an ingredient which readily assumes the 
gaseous form. Thus mercury expands less 
when h bated to a given temperature than- 
water, which boils at a heat much inferior to 
mercury; and alcohol is much more expand- 
ed than water, because its boiling 'tempera- 
ture is lower. Jn like manner nitric acid 
is much more expanded than sulphuric acid; 
not only because its boiling point is lower, 
but because a portion of it has a tendency to 
assume the form of an elastic fluid. We 
may consider it therefore as a pretty general 
fact, that the higher the temperature. neces- 
