After placing the negative and focusing the lens for a clear image on the board, the shutter is set and a bromide paper is placed on the board. The paper is exposed, developed and fixed by the directions that are enclosed in the package of bromide papers.
[Illustration: Making Large Pictures with a Small Camera]
Don't pull a lamp hung by flexible cord to one side with a wire and then fasten to a gas pipe. I have seen a wire become red hot in this manner. If the lamp hung by a cord must be pulled over, use a string.
A Curious Compressed Air Phenomenon [111]
Push a pin through an ordinary business card and place the card against one end of a spool with the pin inside the bore, as shown in the sketch. Then blow through the spool, and it will be found that the card will not be blown away, but will remain suspended without any visible support. This phenomenon is explained by the fact that the air radiates from the center at a velocity which is nearly constant, thereby producing a partial vacuum between the spool and the card. Can the reader devise a practical application of this contrivance?
[Illustration: Experiment with Spool and Card]
** Simple Switch for Reversing a Current [111]
Take two strips of copper or brass and fasten them together by means of gutta-percha (Fig. 1); also provide them with a handle. Saw out a rectangular block about one and one-half times as long as the brass strips and fasten to it at each end two forked pieces of copper or brass, as in Fig. 2. Fasten on the switch lever, as at A and B, Fig. 2, so that it can rotate about these points. Connect the wires as shown in Fig. 3. To reverse, throw
[Illustration: Simple Current-Reversing Switch]
the lever from one end of the block to the other. --Contributed by R. L. Thomas, San Marcos, Tex.
A piece of an old bicycle tire and a glass fruit jar are the only materials required for making this trap. Push one end of the tire into the hole, making sure that there is a space left at the end so that the mice can get in. Then
bend the other end down into a fruit jar or other glass jar. Bait may be placed in the jar if desired, although this is not necessary. --Contributed by Geo. Go McVicker, North Bend, Neb.
A brilliant polish may be given to tarnished nickel by immersing in alcohol and 2 per cent of sulphuric acid from 5 to 15 seconds. Take out, wash in running water, rinse in alcohol, and rub dry with linen cloth.