To operate the trick, grip the stick firmly in one hand, and with the forward and backward motion of the other allow the first finger to slide along the top edge, the second finger along the side, and the thumb nail will then vibrate along the notches, thus making the arm revolve in one direction.  To make the arm revolve in the opposite direction—­keep the hand moving all the time, so the observer will not detect the change which the hand makes —­allow the first finger to slide along the top, as in the other movement, the thumb and second finger changing places:  e. g., In the first movement you scratch the notches with the thumb nail while the hand is going from the body, and in the second movement you scratch the notches with the nail of the second finger when the hand is coming toward the body, thus producing two different vibrations.  In order to make it work perfectly (?) you must or course say “skidoo” when you begin the first movement, and then, no matter how fast the little arm is revolving when changed to the second movement you must say “skidee” and the arm will immediately stop and begin revolving in the opposite direction.  By using the magic words the little arm will obey your commands instantly and your audience will be mystified.  If any or your audience presume to dispute, or think they can do the same let them try it.  You will no doubt be accused of blowing or drawing in your breath, and many other things in order to make the arm operate.  At least it is amusing.  Try it and see.  —­Contributed by Charles Clement Bradley Toledo, Ohio.

** Effects of Radium [116]

Radium acts upon the chemical constituents of glass, porcelain and paper, imparting to them a violet tinge; changes white phosphorus to yellow, oxygen to ozone, affects photograph plates and produces many other curious chemical changes.

** Naval Speed Record [116]

On its official trial trip the British torpedo boat destroyer “Mohawk” attained the record speed of a little over 39 miles an hour.

** How to Enlarge from Life in the Camera [117]

Usually the amateur photographer gets to a point in his work where the miscellaneous taking of everything in sight is somewhat unsatisfying:  There are many special fields he may enter, and one of them is photomicrography.  It is usually understood that this branch of photography means an expensive apparatus.  If the worker is not after too high a magnification, however, there is a very simple and effective means of making photomicrographs which requires no additional apparatus that cannot be easily and quickly constructed at home.