# Page:Popular Science Monthly Volume 90.djvu/160

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��Popular Science Monthly

��Suppose, for example, a near object is situated 8 ft. from the camera and a far object is 15 ft. away. In order to have both in sharp focus, you must find the figure 8 in the column at the left in the table; then follow across until the column headed 15 is found and the number loj/^ will be at their junction, at which the pointer should be set on the focus-scale. This will bring both objects, and all intermediate points, in sharp focus on the plate. If the near object is 5 ft. from the camera and the distant one is 20 ft. the focusing scale should be set at 8 ft. If the near object is 4 ft. from the camera and the far one is more than 30 ft. away, set the focusing pointer at 8 ft. If the near object or point is more than 30 ft. from the camera and the far object is also more than 30 ft., set the focusing pointer at infinity — 100 ft. The last figure in the first column is infinity point and the last column of figures in the table gives the focusing points when the far distant point or object is more than 30 ft. from the camera.

Following is the explanation of the for- mula to find the focusing point mathemat- ically. Two times the far distance multi- plied by the near distance will give the number which should be divided by a number found by adding the far distance to the near distance. The result is the focusing point. — Geo. H. Stipp.

WHEN used for boring very hard wood the blade of a brad-awl is apt to stick in the work so that the handle is pulled from it. This can be overcome to some extent by wetting the tang before driving it in the handle. This will cause a rust which gives a better grip on the wood fibers.

Another and very satisfactory way is to secure the blade as shown in the illustration. Soften the extreme end of the tang by heating it red hot in a flame and allowing

���The softened end of the tang is bent over into the wood to hold it

it to cool slowly; then bend the tip slightly to one side. Ascertain how far the tang

��through the side at right angles to the central hole. When the tang is inserted the softened end should just pass the side hole, which is 14, in. down from the end. A small nail or brad driven in the hole will bend the tang into a hook where it will be imbedded in the wood. The projecting end of the brad can be filed flush with the wood.

��Preventing Melting Frost from Dripping on Window- Sills

WHEN windows covered with frost are heated, the water drips to the sills and sometimes ruins the finish. The same true when a room becomes filled with

���Metal trough on bottom cross-piece of sash to catch drippings from melting frost

��steam. To avoid this condition, fasten a ' small trough just below the pane, with one end slightly lower than the other. A small can or other receptacle may be attached to the nail used at the lower end, to receive the water. — Edgar Morgan.

��I

��To Sharpen a Reed for a Clarinet or Saxaphone

THE reeds used for clarinets and saxa- phones must always be trimmed to take ofl^ the rough edge or to make them

��enters the handle and make a small hole stiffer. It is almost impossible to do this

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