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��Popular Science Monthly
��direction. If we look at the earth through a telescope, however, we limit our field of vision to a comparatively small area, which rushes past so rapidly that we are unable to distinguish a single object. The earth seems to "flow" under us.
If you have carefully followed the foregoing explanations you will be quite able to appreciate fully a drift indicator which has recently been developed and which is regarded' as one of the most im- portant contributions to the science of aviation.
The lubber-line is engraved on a mov- able ring mounted inside the compass and encircling the compass card. A tele- scope, provided with five fine cross-hairs, is mounted at any convenient location and so connected with the lubber-line ring that any movement of the telescope results in a corresponding movement of the ring.
When the aeroplane is flying as in- dicated in Fig. 1, the positions of the lubber-line, the compass card and the cross-hairs of the telescope are as shown in Fig. lA. Looking through the tele- scope the earth appears to flow in the direction of the wavy lines. We know the aeroplane is drifting, and at once we set the cross-hairs to parallel the lines of
���Dust from the mop falls through the sieve and is caught in the dustpan
��drift; the lubber-line is automatically and simultaneously moved in the same direction and to the exact number of de- grees. Fig. 2 shows the aeroplane fol- lowing the course unchanged, but the compass card Fig. 2A indicates our course to be actually northwest and not north. Fig. 3 and 3A show that the pilot has swung his craft around to meet the changed c jnditions. While the aeroplane is heading northeast, the actual line of flight is now due north.
Battery Wax Recipes.
THERE is nothing better for the upper edges of glass cells or open-circuit batteries than hot parafQn. Brushed about the upper edge it pre- vents the sal ammoniac or other fluids from creeping up over the top.
The paraffin can be colored, if neces- sary, with red lead, green dust, or pow- ders of various kinds. Generally the paraffin is used without color, so that it has a frosted appearance when cool.
A black wax for stopping the tops of dry cells and coating the tops of car- bons is composed of tar and pitch in equal parts. These are made into a pasty mass with turpentine heated over a stove, but not over an open flame be- cause the ingredients are inflammable. The compound should be like very thick molasses, so that it can be worked with an old knife.
Another good black wax is composed of paraffin, eight parts ; pitch, one part ; lamp black, one part. Heat the mixture and stir it until thoroughly mixed. Ap- ply with a brush or dip the parts into the warm liquid.
Oil Mop Cleaner and Dustpan
THE oil or polish mop is coming into very general use in homes with finished floors. The dust is quickly picked up in the soft yarn mesh of the mop but the problem of remov- ing the dust from the mop then arises. A special cleaner has been devised which is also a dustpan. One holds it in place with a foot upon the short han- dle, and combs the mop back and forth over a perforated platform, the dust falling into the dustpan beneath. This can be used in the house as well as out of doors.
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