THE WORLD } 'S ADVANCE 



351 



hole in the end of the arm, L, which is 

 locked to the standard. This arm should 

 be insulated, as shown, by a fibre joint. 

 The self-operating device consists of a 

 glass vessel, /, around the upper part of 

 which a layer of heavy magnet wire (No. 

 14 is large enough) is wound. The ves- 

 sel is nearly filled with mercury. The 

 carbon, B, fits in a heavy iron sleeve 

 which sinks into the mercury until its 

 weight and that of the carbon and holder 

 are displaced. 



Current flows from the two binding 

 posts through the coil and mercury and 

 the two carbons, which are touching. 

 The energized coil causes a solenoid ef- 

 fect, drawing the lower carbon down into 

 the mercury until the arc is the correct 

 length. A metal strip, M, is placed across 

 the mercury vat and is bored with a hole 

 of sufficient size to admit the passage 

 of the iron sleeve. In that way the lower 

 carbon is guided. The weight of the 

 mercury pushes the carbon upwards. 



Contributed by 



NOORMAN WlNDERLICH. 



An Elevator Lamp That Insures Safety 



The danger of persons stumbling upon 

 entering- or leaving elevators because of 

 the unequal levels can be eliminated by 

 the use of a lamp having a shielded ray, 



Elevator floor 

 Light 



as shown in the accompanying drawing. 

 The lamp should be attached to the floor 

 of the car by means of a crow-foot, and 

 connected so that it will light when the 

 elevator is stopped. This can be accom- 

 plished by making an extra connection 

 or two at the starting switch. 



Contributed by JOHN J. KUNTZ. 



Sanitary Garbage Pail Container 



Garbage pails, unless they are kept 

 scrupulously clean, draw flies and thus 

 spread disease. The simplest way to 

 prevent this condition is to dig a pit in 

 which a pail large enough to hold the 

 garbage can is placed. Between the larger 



pail and the earth surrounding it a thick 

 layer of coal ashes should be poured and 

 tamped. The smaller pail is placed with- 

 in the larger one, as shown, upon a layer 

 of tamped ashes. The cover of the large 

 pail is elevated a short distance. 

 Contributed by 



FRED KUNCHMAN. 



To Punch Holes in Steel Springs 



Holes may be punched in steel springs 

 or other stiff metal if a plate of thin 

 galvanized iron or brass is placed be- 

 tween the metal and the anvil. Two or 

 three thicknesses may sometimes work 

 better than a single sheet. The punch 

 should have a flat end surface and, pre- 

 ferably, a shank which does not taper. 



Contributed by 



J. C. LINDSTROM. 



Magnetic Scissors That Picks Up 

 Needles. 



A pair of magnetic scissors will be 

 found very useful in the sewing room 

 and elsewhere about the house. It will 

 pick up needles or other iron or steel 

 articles, but will not attract any other 

 metal. This will enable any one to dis- 

 tinguish between brass hooks and iron 

 ones which must not be used on cloth- 

 ing that is to be washed. A small horse- 



