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XI. On the Photographic Spectra of Meteorites. 
By Sir William Crookes, O.M., F.R.S., LL.D ., D.Sc., 6 c , c. 
Received October 19,—Read November 2, 1916. 
[Plates 19, 20.] 
For several years I have been engaged on the spectrum analysis of Meteorites. Many 
meteoric specimens have come into my possession—through the kindness of friends— 
especially am I indebted to the Trustees of the Natural History Museum and t<> 
Dr. Prior, who presented me with specimens of such of the meteorites of which the 
quantity in their possession would not be appreciably diminished by the loss of the 
two or three grms. required for my experiments. 
The Research is divided naturally into the examination of meteoric stones and 
meteoric irons. I propose at present to deal with meteoric stones or aerolites. These 
wonders of the sky consist generally of one or more silicates (mainly olivine and 
bronzite), interspersed with particles of nickeliferous iron, troilite, &c. Recent 
developments have led to many original devices and modification of details in the 
working spectrograph, thus furnishing information which may be of interest to those 
engaged on this branch of spectroscopic analysis. 
As the whole value of the Research depends upon the excellence of my Spectrograph 
I propose to describe certain novel features of the Instrument. In previous papers I 
have already made brief reference to it, and therefore there is no need to describe it 
completely. It is peculiar in this respect; it has been devised and constructed in my 
laboratory for the work it was required to do, by a process of evolution, each part 
having been modified and improved as the work went on—thus in its present form it 
is the outcome of a great deal of experimental construction under working conditions. 
As an instance, I may say that the slit has been reconstructed at least six times— 
each change that the working conditions has rendered necessary making it more 
efficient until now it approaches perfection. 
The Spectrograph. 
The instrument was originally devised for the photography of the ultra-violet region, 
but was ultimately extended so as to include the visible spectrum down to the limit of 
sensibility of the commercial panchromatic plate which is in the neighbourhood of 
VOL. COX VII. A 559. 3 O , Published, December 21, 1!U7. 
