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 diiferent 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. 



