XLI.
PASSAGE THROUGH THE WHOLE SCALE.
534.
The first excitation and gradual increase of colour take place more on the plus than on the minus side. So, also, in passing through the whole scale, colour exhibits itself most on the plus side.
535.
A passage of this kind, regular and evident to the senses, from yellow through red to blue, is apparent in the colouring of steel.
536.
The metals may be arrested at various points of the colorific circle by various degrees and kinds of oxydation.
537.
As they also appear green, a question arises whether chemists know any instance in the mineral kingdom of a constant transition from yellow, through green, to blue, and vice versâ. Oxyde of iron, melted with glass, produces first a green, and with a more powerful