spark spectra of lead, tin, antimony, bismuth, and gold. 227 
separated elements which belong to the same type, in that they 
are divided into the same number of components having similar 
appearances, and whose relative intensities, polarisations and 
distances apart when represented on the same scale of vibration 
numbers, are essentially identical. 
(4) The constituents of some of the triplets, vibrating perpen- 
dicular to the lines of force, are comparable with the constituents 
of some of the quadruplets of the various metals, in being 
polarised in the same direction and in having the same distances 
apart when represented on the above scale of d \/\ 2 . 
I wish again to express my thanks to Professor Liveing for the 
use of his spectroscope. 
