360
JOURNAL OF CHEMICAL EDUCATION
FBBR~ARY, 1930
over it from another negative. Or, one negative or portion of film may be superimposed upon another in a single printing with the same effect. An interesting chapter on this subject, accompanied by several illustrations, may be found in H. Carrington's "The Physical Phenomena of Spiritualism" (Small, Maynard). Printing. A few unusual devices may be used in the printing of pictures. The use of odd-shaped masks can be endlessly varied to give different margins. Pictures can be given a striking canvas effect by placing a thin handkerchief or cloth between the negative and the glass of the printing frame. A simple method by which the amateur may retouch is to make a negative of the print by treating it with a thin oil to give transparency, retouching to taste with crayon, then using this "negative" as any other in printing. Photmicrography on a small scale may be performed by the novice in an extremely simple way. The microscope is focused in the usual way and the lens of the camera is applied to - Fraune d . - S n ~ o GRAINS the eyepiece, the camera focus being set a t muMLowm LEvBL Or AN "infinity." With a 100-watt frosted bulb and OIL WELL reflector as illumination, placed a t a distance of six inches from the stage of the micrq~icope,an exposure of twenty-five to fifty seconds with a diaphragm aperture of sixteen is given. This method affords an interesting procedure for the study of crystals. The accompanying photographs were made through a fifteen-dollar microscope magnifying thirty times (Figure 1). The objects shown are grains of sand from two different levels in an oil well. For light crystals against a dark background (Figure 3) a thin piece of red paper is interposed a t R (Figure 1). For dark crystals against a light background (Figure 4), the shade is placed in position A (Figure 1).
Iceberg Detection. Howard T. Barnes of McGill University, Montreal, Canada, reports that one of the interesting results of the Van Home expedition just returned from iceberg study on the Atlantic was obtained with the submarine microphone detector. Very loud deep noises were heard three miles from an iceberg and hecame faint a t sin miles. These noises are apparently due t o the cracking under water of the iceberg, and they could readily be heard above the usual ship's noises. The succession of cracks was irregular, running from 11 t o 68 a minute. The effect is so characteristic that it is proposed to extend the investigation in the hope of finding a method of iceberg detection.- Nature
