126 
position of this latter must have taken place; the arsenic has 
become oxidised, and crystals of arsenious acid are the result. 
The piece of ore will be deposited in the Society’s mineral 
collection. 
The discovery of these crystals being- pure arsenious acid 
was made by Mr. Bottomley, Mr. Spence’s assistant in his 
laboratory. 
An interesting conversation followed, in which the fact was 
stated that arsenic is a constituent of nearly all the artificial 
manures which have superphosphate of lime as their basis ; 
and in connection with this a report was named of arsenic 
having been found in some of the crops grown with such 
manures. 
Professor Roscoe exhibited the beautiful lithographic map 
representing the dark lines in a portion of the solar spectrum, 
lately published by Professor Kirchhoff. The lines are printed 
in ink of six different shades, and are of six different degrees 
of thickness, so that the leading features of the spectrum can 
be at once recognised. The position of the bright lines pro- 
duced by the incandescent vapour of certain metals is also 
given on the map, and the coincidence of many of these with 
the dark Frauenhofer’s lines rendered evident. 
Professor Roscoe stated that the length of the drawings 
when complete would amount to some twenty feet, and that to 
give an idea of the scale on which the map was made, he 
might remark that the distance between the two double lines 
“ D” is upwards of four millimetres. These maps are as yet 
only printed together with the memoir by Professor Kirchhoff, 
upon the Solar Spectrum and the Spectra of the Chemical 
Elements, in the Transactions of the Berlin Academy ; an 
English edition will, however, shortly be published, giving a 
translation of the original memoir, and containing the same 
drawings of the spectrum as those exhibited, which accompany 
the German text. 
