960 



Popular Science Monthly 



dicular D-C whose value represents the 

 equivalent of the three resistances in 

 parallel. This equivalent combined in a 

 similar manner with the remaining re- 

 sistances of 225 ohms gives us the line F-G 

 whose value according to the above scale 

 is 120 ohms and represents the combined 

 resistances of the four resistances in parallel. 

 With the four resistances selected this 

 result can be easily verified by the usual 

 method of calculation. 



This process may be carried out for any 

 number of resistances. It is evident that 

 the larger the scale selected the more 

 accurate will be the result. The writer 

 has personally found the foregoing method 

 very convenient and more satisfactory than 

 the usual methods, especially where tables 

 of logarithms or reciprocals are not easily 

 available. — F. H. Tillotson. 



Lighting the Dash-Board of an -Auto- 

 mobile from the Side Light 



MANY cars are equipped with the so- 

 called flush side light, the lens be- 

 ing flush 

 with the out- 

 side, and the 

 back of the 

 lamp ex- 

 tending in 

 on the dash. 

 By simply 

 cutting 

 away a sec- 

 tion of the 

 lamp casing, 

 as shown, 

 part of the 

 light will fol- 

 low the dash, 

 thereby illuminating it sufficiently for all 

 needs. — Thos. W. Benson. 



A cut-out on the flush side 

 light to illuminate the dash 



Heating a Soldering Iron with an 

 Electric Arc 



EXPERIMENTERS often find them- 

 selves with some soldering to do, but 

 with no means of heating the soldering iron. 

 Using the iron as one electrode of an arc I 

 found to be a good makeshift. 

 • This suggested the construction of the 

 arc and brackets described herewith. As 

 it is to be used only a short while at a time, 

 and the amperage is small, wood may be 

 used in its construction but it is best to 

 cover the wood with asbestos. Two stand- 



ards are fastened upright upon the base as 

 shown and near the top of each is placed a 

 screw hook (a nail bent up will do) upon 



The soldering iron makes one terminal 

 for the electric arc which heats it 



which the iron is to rest. A lever having a 

 hole bored at one end, in which is inserted 

 an ordinary }^-in. arc light carbon is 

 pivoted at its center on a bolt which runs 

 through the middle of the upright. The 

 nut is tightened just enough to hold this 

 lever in whatever position it is placed. As 

 the carbon burns away, adjustment is made 

 with this lever. One binding-post is con- 

 nected with the hook which supports the 

 iron and the other is connected by a 

 flexible cord with the set screw which holds 

 the carbon in the lever. 



This is connected with the line by a 

 resistance in series. A water rheostat 

 which is easily constructed and regulated 

 may be used, or a wire rheostat may be 

 constructed. For a medium-size iron I 

 found 3 amperes was about right. Lower- 

 ing the resistance will increase the current 

 and consequently the heat of the iron. If 

 direct current is used it is best to connect 

 the positive wire with the carbon, as this 

 will avoid the possibility of pitting the 

 iron. — Kenneth M. Bard. 



Sheet Asbestos to Make a Packing 

 for Steam Chests 



OWING to the heat imparted to the 

 cylinders and steam chests of steam 

 engines, rubber packing does not give as 

 good service and last as long as it should. 

 After some experimenting, the writer has 

 found that a sheet of asbestos 1/16 in. 

 thick makes a good packing for a team 

 chest. This material is very cheap, and 

 if put on the engine* wet, will stand a 

 pressure of 150 lb. As an experiment, a 

 joint made with the asbestos sheeting was 

 taken apart and put together five times 

 and still held its shape. Experience shows, 

 that it makes just as tight a joint as the 

 best rubber packing. — W. S. Standiford. 



