Theory of Nobili's Coloured Rings. 



17 



sulphate and carbonate of lead, and is much less than that of 

 the metal. 



If therefore the radii of the dark and light rings, when 

 monochromatic illumination is used, are measured, the even 

 products of the cubes of the radii in the case of the dark rings, 

 and the uneven products in the light rings should yield nearly 

 constant values. To produce monochromatic illumination I 

 used the flame of alcohol, into the wick of which common 

 salt had been rubbed. This light is undoubtedly more pure 

 than the red light which is produced by coloured glass. The 

 following tables will show how far experiment approximates 

 to calculation : — 



Coloured rings upon silver gilt. 



Table III. 



Battery of Three Elements. 



Table IV. 

 Battery of Four Elements. 



Phil. Mag. S. 3. Vol. 33. No. 219. July 1848. 



