The great pyramid passages and chambers

PLATE CXXIII.

495 The method which we have found satisfactory is to use magnesium in powder form, with some preparation added in order to make it explode when ignited. The specially prepared powder which we use is named the “ Agfa” flashlight, and we find that a small quantity is sufficient to enable us to photograph even a large place, such as the Subterranean Chamber. We form a little heap of the powder (varying in size according to the photograph to be taken) in the centre of the lid of a metal box. Into this we insert one end of a strip of touch-paper; and then, all other things being ready, we set light to the paper and retire, shutting our eyes, and holding our hands to our ears. The glare of the flash is so intense that we have found it necessary to keep our eyes closed whenever possible; and the noise, increased ten times by the resounding echoes throughout the passages, is rather disconcerting. (We wonder what the bats think of it all!) As the flash is instantaneous, the photograph is secured before the inevitable smoke (which is not dense in this powder) has had time to settle. At first we inclined to put the lid holding the powder too near the front of the camera, with the result that a number of the negatives were spoiled

The mouth of the air-channel in the south wall of by the light fanning out in front of

the King's Chamber. the lens. We had, of course, to retake these photographs.

496 It is impossible to make use of the focussing-screen of the camera in the ordinary way in these dark recesses of the Great Pyramid, but the correct focus is easy to obtain by means of adjustable scales, which indicate the proper distance of the lens from the sensitive film, relative to the distance that the camera is erected from the part to be photographed. As the aperture of the wide-angle lens is very small (only f/22 to f/32), most objects in the field of view, whether close to the camera or at a distance, are sharply defined.

497 We photographed the mouth of the south air-channel of the King’s Chamber as it appears on the south wall—Plate CXXIII. The surface of the wall immediately above and to the east side of the mouth is much broken away, and the opening is therefore much larger than it was originally. This air-channel runs horizontally southward for a few feet, then takes a bend upward, and after a second short length still another upward

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