15 
work the metallic colours are left out, 
because, were they given, they would 
soon tarnish ; and they are in some mea- 
sure unnecessary, as every person is well 
acquainted with the colour of gold, silver, 
brass, copper, &c. Also the play and 
changeability of colour is left out, as it is 
impossible to represent them ; however, 
they are well known to be combinations 
of colours, varying as the object is changed 
in position, as in the pigeon's neck, pea- 
cock's tail, opal, pearl, and other objects 
of a similar appearance. To gain a tho- 
rough knowledge of colours, it is of the 
utmost consequence to be able to distin- 
guish their component parts. Werner 
>' 
1 
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