MAR 
grow : thus, since 19, or the third of 57, 
is the expectation of two joint lives whose 
common age is 29, or common complement 
57, 20 marriages every year between per- 
sons of this age would, in 57 years, grow to 
20 times 19, or 380 marriages always ex- 
isting together. The number of survivors 
also arising from these marriages, and al- 
ways living together, would, in twice 57 
years, increase to the same number. More- 
over, the particular proportion that be- 
comes extinct every year, out of the whole 
number constantly existing together of sin- 
gle or joint lives, must, wherever this num- 
ber undergoes no variation, be exactly the 
same with the expectation of those lives at 
the time when their existence commenced. 
Thus, if it were found, that a nineteenth 
part of all the marriages among any body 
of men, whose numbers do not vary, are 
dissolved every year by the deaths of either 
the husband or wife, it would appear, that 
19 was, at the time they were contracted, 
the expectation of these marriages. 
Dr. Price observes, that the annual ave- 
rage of weddings among the ministers and 
professors in Scotland, for the last 27 
years, has been 31 ; and the average of 
married persons, for 17 years ending in 
1767, had been 667. This number, divided 
by 31, gives 2ir, the expectation of mar- 
riage among them-; which, he says, is 
above two years and a half more than the 
expectation of maj iiage woidd be, by Dr. 
Halley’s table, on the supposition that all 
first, second, and third marriages, may be 
justly considered as commencing, one with 
another, so early as the age of 30 ; and he 
has proved, that the expectation of two 
equal joint lives, is to the expectation of a 
single life of the same age, as two to three : 
consequently, the expectation of a single 
life at 30, among the ministers in Scotland, 
cannot be less than 32.25. If we suppose 
the mean ages of all who marry annually to 
be 33 and 25, the expectation of every 
marriage would be 19 years ; or, one with 
another, they would be all extinct in 19 
years : the marriages w'hich continue be- 
yond this term, though fewer in number, 
enjoying among tliem just as much more 
duration as those that fall short of it enjoy 
less. But it appears from the observations 
and tables of M. Muret, that, in the district 
of Vaud (dividing half the number of mar- 
ried persons, viz, 38,328, by the an- 
nual medium of weddings, viz. 808) the 
expectation of marriage is only 23i years : 
*0 much higher are the probabilities of 
MAR 
life in the country than in towns, or than 
they ought to be, according to De Moivre's 
hypothesis. See Price’s Anncitii^s. 
MARROW, in anatomy, a soft oleagi- 
nous substance contained in the cavity of 
the bones. 
MARRlJBIUM, in botany, horehound, 
a genus of the Didynamia Gymnospermia 
class and order. Natural order of Verticil- 
latse. Labiatae, Jussieu. Essential charac- 
ter : calyx salver-.shaped, rigid, ten-streaked ; 
corolla upper lip bifid, linear, straight. 
There are eleven species. These plants are 
chiefly preserved in botanic gardens for the 
sake of variety. 
MARS, in astronomy, the planet that 
revolves next beyond the earth in our 
system, is of a red fiery colour, and always 
gives a much duller light than Venus, though 
sometimes he equals her in size. He is not 
subject to the same limitation in his motions 
as Mercury or Venus, but appears some- 
times very near the sun, and at others at 
a great distance from him ; sometimes rising 
when the sun sets, or setting when he rises. 
Of this planet it is remarkable, that when 
he approaches any of the fixed stars, which 
all the planets frequently do, these stars 
change their colour, grow dim, and often 
become totally invisible, though at some 
little distance fi-om the body of the planet; 
but Dr. Hersciiel thinks this has been ex- 
aggerated by former astronomers. Mars / 
appears to move from west to east round 
the earth. The mean duration of his side- 
real revolution is 686.979579 days. His 
motion is very unequal. When we first 
perceive this planet in the morning when 
he begins to separate from the sun, his mo- 
tion is direct, and the most rapid possible. 
This rapidity diminishes gradually, and the 
motion ceases altogether, when the planet 
is about 137“ distant from the sun ; then hi.s 
motion becomes retrograde, and increases 
in rapidity till he comes into opposition witli 
the sun. It then gradually diminishes again, 
and becomes nothing when Mars approaches 
within 137° of the sun. Then the motion 
becomes direct, after having been retro- 
grade for seventy-three days, during which 
interval the planet described an arc of 
about 16°. Continuing to approach the sun, 
the planet at last is lost in the evening rays 
of that luminary. All these diflFerent phe- 
nomena are renewed after every opposition 
of Mars, but there are considerable difter- 
enc-3s both in the extent and duration of 
his retrogradations. 
Mars does not move in the plane of the 
