Fig. 8.
When the same experiment was repeated in orange, yellow, green, blue, indigo, and violet light, the very same phenomenon was observed; with this difference only, that the rings were largest in red light, and smallest in violet light, and had intermediate magnitudes in the intermediate colours.
If the observer now places his eye below E, so as to see the transmitted rays, he will observe a set of rings as before, but they will have a bright spot in their centre at E, and the luminous rings will now correspond with those which were dark when seen by reflection, as will be readily understood from inspecting the preceding diagram.
When the object-glasses are illuminated by white light, the seven systems of rings, formed by all the seven colours which compose white light, will now be seen at once. Had the rings in each colour been all of the same diameter they would all have formed brilliant white rings, separated by dark intervals; but, as they have all different diameters, they will overlap one another, producing rings of various colours by their mixture. These colours, reckoning from the centre E, are as follows:—
1st Order. Black, blue, white, yellow, orange, red.
2d Order. Violet, blue, green, yellow, orange, red.
3d Order. Purple, blue, green, yellow, red, bluish-red.
4th Order. Bluish-green, green, yellowish-green, red.
5th Order. Greenish-blue, red.
6th Order. Greenish-blue, red.