Alexandria gazette. [volume] (Alexandria, D.C.) 1834-1974, 1881-02-17

At the Mldlaod Institute recently, Professor
W. h. Ayrton delivered lecture in which, bav
ing given some additional explanation of the
methods of measuring minute periods of time,
ne spoke of million Of yeels. The words, "a
million years" how gby they are uttered. but
how little did ono think what they meant. To
c9unt million, ono, two, three aud So 90, at
the rate of two second, and d voting SIX hours
day to the work, would occupy twenty three
days, or moro than three weeks. The lecturer
asked his hear II to think of million of people
10 comparison With tho po?rlatiop of Birmipg-
h1U; and OF 8 million pounds sterling a sum
which, al 5 per can't interest would yield $50 00O
year. With regard to the period OF a million
years, he showed that, great IS it was. the
measurement OF tlme by millions of years WAS
applicable to he existence OF the earth, In
reply to the question of whether the earth's
existence vas tu be counted by thousands or by
millions of years. he called attention to the
geological evidences of orgaric changes on the
esrth's surface which required DOT mu,h less
than hundred million years for the earth's
age. There Was however, better method of
spproXimating TO the age of the earth. The
changes of temperature belonging TO the differ.
81 seasons were less percepubly felt rs they
depth of about fifty feet tho temperature was
practically constant If however, they coutin.
ued TO descend an Increase of temperature WAS
experienced st about the rate of one degree per
fifty feet of the descent. Supposng this increase
went on st the same rate until the center of fha
Xlohe WIS reached the temperature there would
be 4QO,OUO degrees higher than at the surface
IIere WIS, however no reason 10 assu me that
the increase did 20 on or that the Temperature
at the center was higher than that OF molten
rock, 7,UU dagrees or at most 10 600 degrees.
Assuming this 20 be the temperature 1T the
center, and knowing, by experiment, the cor-
ducung power OF rock in relation to heat Sir
William Thomson WAS able to cslculste The
present distr! button of temperature throughout
the whole eart:,. not only the present dsi.ibu-
tlon downward, but the distribution at any
future and et any past time Taking the tenn.
peratnre At I UOO degrees ss having been once
the uniform temperature of the whole BODY, the
result or The cSlcu atloIs WAS that the earth
hsd been hundred million years in cooling.
The lecturer showed by q cooling of q sauce
pan OF compressed sand which had been heated
to uniform temperature, that the cooling of
the center went on very slowly, but at points
near the outside surface it was tolerably rapid.
being. IN fact, the more rapid the nearer the
poi AZ wss to the s1rfsHe. Sir William Thomson
had shown that in l(o 0CO eco years the cooling
would not have descended more than 100 miles
below The surface. and that it would not be for
more ihsn l 600 600 QUO years t,t the cooling
would have any effect a. all at 5G3 miles below
tho surface The lecturer, in conclusion, com.
DATED The '1es that the center of the earth WIS
now IN liquid state, and submitted some eddi.
tonsl cons 1eratlons, teuding to sbop that it
was not much more thar 100 nOU OoO vos-s
since the earth soidiied.-EngLish Mechanic.