Hepworth, Thomas Cradock, -1905 · London : Hazell, Watson, and Viney · leaf 193
181 AMATEUR PHOTOGRAPHERS. one reaches a certain depth, its edge must obscure a per- ceptible amount of the available light. This was first discovered about twelve years ago, at the time some experiments were being carried out at the South Foreland, in order to ascertain the be^t disposi- … Fig. 64. obtained by sloping the carbon rods, while at the same time the lower one is in advance of the upper one, so that the interior of the positive crater is turned towards the direction in which the light is required to stream. This idea is well carried out in a form of regulator which has…
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