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2. On a New Variety of Ocular Spectrum

Published online by Cambridge University Press:  15 September 2014

John Aitken
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Extract

If we look for a short time at any object, and afterwards turn the eye in another direction, we see a spectral image of the form of the object first looked at.

Again, if after we have looked at any coloured object we turn the eye in another direction, we see a spectral image of a colour complimentary to that first looked at.

In addition to these spectral forms and colours, I find there is another and distinct kind of ocular spectrum, which we may call a motion spectrum. It is seen when we look first at a body in motion and afterwards direct the eye towards an object at rest. The object at rest, when seen under these conditions, seems to be in motion, and the direction of its apparent motion is the opposite of that of the moving body first looked at.

Type
Proceedings 1878–79
Information
Proceedings of the Royal Society of Edinburgh , Volume 10 , 1880 , pp. 40 - 44
Copyright
Copyright © Royal Society of Edinburgh 1880

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References

page 41 note * Report of the British Association, 1877.

page 41 note † The discs used in the experiments were from 22 cm. to 44 cm. in diameter. The number of parts into which the disc is divided does not seem to be of much importance, If divided into fewer parts, then it simply requires to be driven at a greater velocity. If divided into 24 parts, it can easily be driven quick enough with a handle on the opposite end of the shaft without the aid of multiplying gear.

page 41 note ‡ The disc should be rotated at such a rate that the eye cannot distinguish the black and white divisions, but not so quick that they are blended together.

page 42 note * The markings on the paper should not be too strongly contrasted with the paper. White paper roughly spotted over with ink will do, but the effect is greatly increased when the contrast is not so great. The best effect is produced by first washing the paper all over with Indian ink, thick enough to make the paper a darkish grey, and, while still wet, daubing it all over with Indian ink. In the absence of anything better, a cocoa-nut fibre mat does well.