Year: 1860

out of their paths by the attractions OF the earth
and moon. Ills to venture the expression
of an opinion Of my own, shOuldineline toadOpt
this theory.


Allowing, then, that aerolites are portions oil
bodies foreign to the earth, which become mo
mentariIy luminous as they pass through our at
mosphere, it only remains to assign reason for
this momentary brightness, and for the heat
which manifestly attends it, and is made evident
by the accompanying explosions and the yitrifac-
ton of the fragments which fall Twenty years
ago, this problem was less easy of solution than
tits to-day; although twenty years ago the cause
was stated generally, in the same terms as now.
This cause is the resistance which the moving
masses encounter in theirpassage through the at
mosphere. The relation of heat to force, and of
force to heat and the controvertibility Of either
into the other, are matters of comparatively re-
cent discovery. 1t may now be computed with
rigid exactncss what amount of heat may be pro-
duced by the expenditure of any given amount
of force





If its motion be arrested or checked, the force
thus apparently destroyed is converted into heat
We're the earth which moves at the rate ofabout
nineteen miles per second, to be suddenly brought
to rest by striking an immoyable obstacle, the
heat generated would be equal to that which
would be produced by the instant and complete
combustion of nearly eighteen times its own
weight of COAL and would raise the temperature
of the whole mass to point about five hundred
times hotter than that of the hottest wind furnace
and more than six hundred times hotter than
melted iron as It flows from smelling furnace


Were body to fall from the point of equilib-
rum between the earth and moon, it would enter
the atmosphere with velocity only about third
as great as that of the earth in its orbit and as
the forces represented by moving masses are as
the squares of the veloctics, its hcat-producing
power would be but one-ninth as great. We're
such body to be suddenly arrested its temper
ature would be raised to about seventy times that
of melted iron; and were it only to be retarded,
it would become heated in proportion to the re-
tardation.


Thcactual retardation ola body moving thro'
the air will vary with the magnitude and density
of the mass; but small body-say one ofa foot
in diameter, and of the average density of meteor
c stoncs-though falling vertically downward,
and therefore constantly urged by gravity and
though entering the air with the velocity of six
and one half miles, acquired in falling from the
moon, would soon be reduced to the uniform We
locity of quarter of mile per second. What
the actual velocity of fmeteoric bodies is IL is DIFF
fcult to determine. They are seen but for few
scconds-they are rarely seen by practiscd OBJ
servers-and those who see them are usually so
taken by surprise, that the statements made by
thomas to duration, and direction, and length of
track, are often very discordant. But whatever
il may be- there sort of doubt that it must bc
very sensibly reduced, during their flight through
the atmosphere ; and the reduction will be most
considerable in given time, in the case of those
whose original vclocitics are highest. DIR. Bow
ditch estimated the velocity of the Weston mctc-
or (Connecticu) in 1907, at three miles second
Mr. IIerrick deduces three miles and half from
the reported observations but expresses his be-
licfthat the observers made the duration at least
three times too great, and consequently, that the
velocity must have been at least ten miles per sec
ond. These, Of course, are the estimated ycloci-
tics during the period Of the visibility of the me-
tcor. But the body could not have become visi-
bic until after becoming highly heated; and there
fore the initial velocity can only be conccturcd.


If Dr. Bowdtch's estimate is correct for the
Weston meteor, and if the original velocity had
been that acquired by falling from the point of
equilibrium between the earth and moon, then
there must have been reduction of more than
halfthe original velocity, and therefore of more
than thrcc-quarters of the force; or, in other
words, there must have been generation of heat
sufficient to elevate the temperature of the body
to poin. nearly fifty times above the heat of
melted iron. This supposes the conversion into
heat Of the entire force lost A considerable por-
ton oft is however merely transferred to the por-
tons of the air which the meteor sets into motion:
and another portion is expended in raising tho
temperature of the same air. Making every
abatement demanded by these considerations,
and allowing also, that the actual retardation,
owing to the rarity of the upper air, may be much
less than assumed above, there still remains an
abundantly satisfactory explanation of the lu.
mhosity, tho explosion, and the fusion and vitri-
faction ofthese bodies; while the greater heat at
the surface than in the interior, is accounted for
by the fact that the resisting force is applied d.
rcctly at the surface.


have thus endeavored to answer your inqui-
ries as briefly as the nature of the subject would
permit III have told you little which you did
not know before, it must be attributed to the fact
that science has really, upon this subject, so lit
tie to tell


am, Sir, respectfully, etc,


F. A. p. BARNARD.