Optical Phenomenon

Abstract

A SHORT time ago I was lying, during the heat of the day, in a darkened room in a house at one of the hottest stations in India. There was a great glare of sunlight outside. All at once I became aware of figures moving about on the opposite wall. On examination they proved to be the inverted images of the servants of the establishment who were walking about in the performance of their several duties in the gravelled courtyard outside the house. The white colour of their clothes, the dark colour of their skin, and the red colour of their sashes or turbans, were distinctly reproduced, and every servant was recognisable without difficulty. The images were produced by rays passing through three or four holes in the Venetian shutters ; and while they all remained open there was a large penumbra round the images, but on closing all but one hole, this was very much reduced. The holes were of the size of a shilling or half-crown, and made in an outer door as well as the shutter, having been constructed to admit of a punkah rope passing through. The explanation appears to be this :—The sun was above and slightly behind the house. The solar rays falling on the objects in the court-yard were transmitted through the shutter holes. There being no other light in the room, and the rays being strongly scattered by the rough whitewashed wall, the rays were sufficiently powerful to produce an image on the retina of an observer in whatever part of the room he might be ; the room became, as it were, the box of a large camera.