Bauhaus-Universität Weimar

495 
April 5, 1877] NA T U RE 
It is indeed a strange fact that any one of us sitting 
quietly at his table could, on being told the two numbers 
just mentioned, draw out a curve on ruled paper, from 
which thousands of vertical lines might be chalked side 
by side on a wall, at the distance apart that is taken up 
by each man in a rank of American soldiers, and know 
that if the same number of these American soldiers taken 
indiscriminately had been sorted according to their heights 
and marched up to the, wall, each man .of them would find 
the chalked line which he found opposite to him to be of 
exactly his own height So far as 1 can judge from the 
run of the figures in the table, the en-or would never 
exceed a quarter of an inch, except at either extremity of 
the series. 
The principle of the law of deviation is very simple. 
The important influences that acted upon each pellet were 
the same ; namely, the position of the point whence it was 
dropped, and the force of gravity. So far as these are 
concerned, every pellet wo’Jtd have pursued an identical 
path. But in addition to these there were a host of petty 
disturbing influences, represented by the spikes among 
which the pellets tumbled in all sorts of ways. The 
theory of combination shows that the commonest case is 
that where a pellet falls equally often to the right of a 
spike as to the left of it, and therefore drops into the 
compartment vertically below the point where it entered 
the harrow. It also shows that the cases are very rare of 
runs of luck carrying the pellet much oftener to one side 
than the other, . The law of deviation is purely numeri¬ 
cal ; it does not regard the fact whether the objects 
treated of are pellets in an apparatus like this, or shots 
at a target, or games of chance, or any other of the 
numerous groups of occurrences to which it is or may be 
applied.1 
I have now done with my description of the law. I 
know it has been tedious, but it is an extremely difficult 
topic to handle on an occasion like this. I trust the 
application oi it will prove of more interest. 
{To be continued 
ON THE STRUCTURE AND ORIGIN OF 
METEORITES* 
THE study of meteorites is naturally divisible into 
several very distinct branches of inquiry. Thus in 
the first place we may regard them as shooting stars, and 
observe and discuss their radiant points and their relation 
to the solar system. This may be called the astronomical 
aspect of the question. Then, when solid masses fall to 
the ground, we may study their chemical composition as 
a whole, of that of the separate mineral constituents ; and 
lastly, we may study their mechanical structure, and apply 
to this-investigation the same methods which have yielded 
such important results in, the case of terrestrial rocks. 
So much has been written on the astronomical, chemical, 
and mineralogical aspect of my subject by those far more 
competent than myself to deal with such questions, that I 
shall confine my remarks almost entirely to the mechani¬ 
cal structure of meteorites and meteoric irons, and more 
especially to my own observations, since they will, at all 
events, have" the merit of greater originality and novelty. 
Time will, however, not permit me to enter into the detail 
even of this single department of my subject. 
. In treating this question it appeared to me very desir¬ 
able to exhibit to you accurate reproductions of the natural 
objects, and I have therefore had prepared photographs 
of my original drawings, which we shall endeavour to 
show by means of the oxyhy drogen lime-light, and I shall 
modify my lecture to meet the requirements of the case, 
1 Quetelet, apparently from habit rather than theory, always adopted the 
binomial law of error, basing his tables on a binomial of high power. It is 
absolutely necessary to ihe theory of the present paper, to get rid of binomial 
limitations and to consider the law of deviation or error, in its exponential 
form. . , 
2 Abstract of lecture delivered by H. C Sorby, F.R.S., &c., at tne 
Museum, South Kensington, on March 10. • . 
exhibiting and describing special examples, rather than 
attempt to give an account of meteorites in general 
Moreover, since the time at my disposal is short, and their 
external characters may be studied to great advantage at 
the British Museum, I shall confine my remarks as much 
as possible to their minute internal structure, which can 
be seen only by examining properly prepared sections 
with more or less high magnifying powers. 
By far the greater part of my observations were made 
about a dozen years ago. Î prepared a number of sections 
of meteorites, meteoric irons, and other objects which 
might throw light on the subject, and my very best thanks 
are due to Prof. Maskelyne for having most kindly allowed 
me to thoroughly examine the very excellent series of 
thin sections, which had been prepared for him. During 
the last ten years my attention has been directed to very 
different subjects, and I have done little more than collect 
material for the further and more complete study of 
meteorites. When I have fully utilised this material I 
have no doubt that I shall be able to make the subject far 
more complete, and may find it necessary to modify some 
of my conclusions. I cannot but feel that very much more 
remains to be learned, and I should not have attempted 
to give an account of what I l*ave so far done, if I had 
not been particularly asked to do so by Mr. Lockyer. At 
the same time I trust that I shall at all events succeed in 
showing that the microscopical method of study yields 
such well marked and important facts, that in some cases 
the examination of only a single specimen serves to decide 
between rival theories. 7 • 
In examining With the naked eye an entire or broken 
meteorite we see that the original external outline is very 
irregular, and that it is covered by a crust, usually, but 
not invariably black, comparatively thin, and quite unlike 
the main mass inside. This crust is usually dull, but 
sometimes, as in the Stannern meteorite, bright and shin¬ 
ing, like a coating of black varnish. On examining with 
a microscope a thin section of the meteorite, cut perpen¬ 
dicular to this crust, we see that it is a true black glass 
rilled with small bubbles, and that the contrast between it 
and the main, mass of the meteorite is as complete as 
possible, and the junction between them sharply defined, 
except when portions have been injected a short distance 
between the crystals. We thus have a most complete 
proof of the conclusion that the black crust was due to 
the true igneous fusion of the surface under conditions 
which had little or no influence at a greater depth 
than -rivth of an inch. In the case of meteorites of dif¬ 
ferent chemical composition, the black crust has not re¬ 
tained a true glassy character, and is sometimes j^tb of 
an inch in thickness, consisting of two very distinct layers, 
the internal showing particles of iron which have been 
neither melted nor oxidised, and the external showing that 
they have been oxidised and the oxide melted up with the 
surrounding stony matter. Taking everything into con¬ 
sideration, the microscopical structure of the crust agrees 
perfectly well with the explanation usually adopted, but 
rejected by some authors, that it was formed by the fusion 
of the external surface, and was due to the very rapid 
heating which takes place when a body moving with 
planetary velocity rushes into the earth’s atmosphere—a 
heating so rapid that the surface is melted before the heat 
has time to penetrate beyond a very short distance into 
the interior of the mass. . 
When we come to examine the structure of the original 
interior part of meteorites, as shown by fractured surfaces, 
we may often see with the naked eye that they are 
mottled in such a way as to have many of the characters 
of a brecciated rock, made up of fragments subsequently 
cemented together and consolidated. Mere rough frac¬ 
tures are, however, very misleading. A much more 
accurate opinion may be formed from the examination of 
a smooth flat surface. Facts thus observed led Reichen- 
bach to conclude that meteorites had been formed by the
        

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