Note 10 — Chapter I

Diffraction effects may be observed without a microscope, indeed, the more striking are seen in connection with telescopic vision. A beautiful series of phenomena in illustration of the diffraction of light may be produced as follows: Draw on a large sheet of paper a series of geometrical figures, arranged at equal distances in a circle. A collodion photographic picture of these being taken, a series of small transparent apertures in the elsewhere opaque film will result. This film is then mounted, so that it may be in turn brought before the centre of a small hand telescope, previously adjusted to view an image of the sun. In this way we have an apparatus of the most compact form, and by means of which a series of fifty or more phenomena may be brought into view in a few minutes. These pictures being very small (occupying on an average area one-tenth of an inch in diameter), inaccuracies of surface and substance of the glass may be neglected. A film of Canada balsam with which the glass is cemented over the picture produces no disturbance. There is a manifest advantage in the figures being small, as the size of the image is in inverse proportion to the size of the aperture.