SIR W. CROOKES ON THE PHOTOGRAPHIC SPECTRA OF METEORITES. 
426 
aerolites; the experiments were therefore continued, blocks made in the same way 
as in the experiments with chromium were used as electrodes for the arc. The 
proportion of nickel was from 2 per cent, down to 0'04 per cent.—photographs of the 
spectrum were made under the usual working conditions. The portion of the 
spectrum taken was that containing the chromium group, A 3578'840, A 3593'633. 
A 3605'478, and the closely adjacent nickel lines ; it was found that when the amount 
of nickel was reduced to 0'04 per cent, the line 3619'391 was only just visible. 
The information gained from these mixtures of chromium and of nickel made it 
possible to obtain an approximate estimate of the quantities of these elements 
present in the three aerolites, El Nakhla, Aubres, and Bustee. A mixture 
containing chromium 0'25 per cent, and nickel 0'04 per cent, gave a photograph 
which for Cr-Ni was practically identical with that of Aubres. 
The estimation made in this way cannot be more than a “good approximation on 
account of unavoidable variations, due to intensity of light and time of exposure ; 
also to conditions of photographic development, which cannot be exactly controlled, 
but the indications given by the relative intensities of closely adjacent Ni and Cr 
lines when they occur on the same film are very much more exact, and the result 
proves that in these aerolites the element chromium exists in greater abundance than 
nickel. 
To this fact must be added that of the almost total absence of chromium in the 
familiar nickeliferous irons of the siderites. 
In a general survey of the spectrum analyses of the 30 aerolites which forms the 
subject of this Paper, the most striking fact is their similarity in composition, and 
the small number of elements represented. Making full allowance for wide 
differences in the photographic activity of the arc spectra of the elements, it is 
remarkable that we only see with certainty the lines due to some ten bodies, and of 
these ten, four only—iron, chromium, magnesium, and nickel -appear to be present 
in quantity. With three exceptions, Bustee, El Nakhla, and Aubres, the proportion 
between these elements appears to be practically the same in all. 
This suggests that these earthy meteorites must have a common origin, and that 
origin might be due to the disruption of a body in which the process of cosmial 
evolution has been completed ; in short, may we not conclude that the aerolites are 
fragments of a finished and cooled planet. It is possible that we have in our 
museums fragments of a world unrealised—a world that at one time had its place 
between Jupiter and Mars in our planetary system. 
From the results of my unfinished notes on the spectrum analyses of meteoric 
irons, to which I have already referred, it would appear that either the siderites are 
of a different origin, or that they have constituted the solid nucleus or core, from 
which by some process at present unknown the chromium and other elements had 
been separated, leaving the magnetic elements iron - and nickel as the familiar 
ferro-nickel meteorites. 
