144 



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. 



Fastening Brad-Awl Blades Securely 

 in Handles 



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 



