Hence 



1824.] Apparatus for producing Instantaneous Light. 365 



be cleaved with ease parallel to the terminal plane P, and less 

 distinctly parallel to M and M' of the annexed figure. 

 an oblique rhombic prism appears to be its 

 primary form. 



PonM.orM' 109° 



P on h 122 



Pone' 106 



h on c 131 



M on h 128 



31' 



20 

 20 

 20 

 40 



MonM' 77 20 



Acetate of Barytes. 



From the crystals of this salt with which Mr. Cooper has sup- 

 plied me, it appears that the primary form is a right oblique- 

 angled prism. There is a bright cleavage 

 parallel to T, one less bright parallel to M, 

 and an indistinct one perpendicular to 

 these. 



M on/ 146° 18' 



MonT 113 12 



Monrf 116 56 



dond' 126 8 



Ton/" 100 30 



Article IX. 



Apparatus for producing Instantaneous Light. By the Rev. 

 J. Gumming, MA. FRS. Professor of Chemistry in the Uni- 

 versity of Cambridge. 



(To the Editor of the Annals of Philosophy.) 



DEAR SIR, Ctimbiidge, April 15, 1824. 



In the early part of last December, I exhibited to our Society 

 Doebereiner's experiment, of the inflammation of hydrogen in 

 atmospheric air by precipitated platina ; and from that time to 

 the present have occasionally employed the same apparatus for 

 producing an instantaneous light. The method I have used is 

 so simple, that I should not have thought, it worth communicat- 

 ing, if I had not been told that (he instruments made in London 

 for this purpose lose their effect alter a few experiments. 



Having removed the electrical apparatus from a Volta's lamp, 

 I placed a fragment of precipitated platink between two pieces 

 of watch spring, which are inserted into a cork fitting into a 

 small test tube as a cap. The distance of the platina from the 



