THE IRBIGATION AGE. 



213 



PRACTICAL CURRENT METER. 



BY CURT H. EIFFERT AND C. A. BOCK, ENGINEERING 

 DEPARTMENT, CORNELL COLLEGE, IOWA. 



dry battery is sufficient to operate the sounder. The 

 machine as actually constructed, complete with record- 



The accompanying illustrations show the result 

 of an attempt to produce a cheap yet practical current 

 meter. The instrument was designed merely for experi- 

 . mental purposes, but since its completion and success- 

 ful trial there seems to be no reason why similar ma- 

 chines could not be constructed for practical use. 



The materials needed for the outfit are some rather 

 stiff sheet tin, a good tin can cover about three inches 

 in diameter, a good knitting needle or other light steel 

 shaft, some insulated copper magnet wire, a small iron 

 bolt, a small strip of sheet copper and a dry battery. 

 The wheel is made of the can cover. First the cover 

 is accurately centered and a hole punched to fit the 

 shaft. Next the blades of the wheel may be cut as 

 shown by the dotted lines in Fig. 3. The turned-over 

 rim of the cover, which ought not be more than 14 

 inch wide, is left intact, fastened to and stiffening the 

 wheel at the uncut parts at the outer edge of the blades. 

 The blades may now be bent back to the proper angle 

 along the lines 1, Fig. 3. To the shaft is fixed a small 

 wooden cylinder s, Fig. 2, carrying a longitudinal nar- 

 row strip of copper c. The body of the machine con- 

 sists of a tin cylinder containing suitable bearings for 

 the shaft, with a thrust bearing in the rear. A hole is 

 cut in the top of the cylinder through which to make the 

 electric connections. The parts of the cylinders, with 

 the shaft and its bearings, must be carefully assembled 

 and well soldered. This requires a little accurate work, 

 but can be quickly and neatly done by any tinsmith. 

 The tail is made of two flat pieces of heavy sheet tin, 

 each cut with a slit half way along the center line from 

 opposite ends. These are well soldered together at 

 right angles and soldered to the rear end of the cylin- 

 der. A small cylindrical box b, Fig. 2, with a hole in 

 the end slightly larger than required for the shaft, is 

 soldered to the cylinder. When filled with oil this lit- 

 tle box effectually prevents water from entering the 

 machine. Now the wheel may be soldered to the front 

 end of the shaft. The electric connections are made by 

 means of two copper strips d, Fig. 2, fixed in a block 

 of wood w, which fits the opening in the cylinder. These 

 are so bent as to come in perfect contact with the strip 

 c, at every revolution of the shaft, and yet rub lightly 

 enough to obviate needless friction. When the block 

 is carefully adjusted it is fixed in place by melting 

 around it the pitch from the top of an old dry cell. 

 The binding posts p, are also taken from an old dry 

 cell, connected one each with the copper strips A, and 

 fixed in place by surrounding with pitch. This con- 

 trivance is further strengthened by a band of heavy tin 

 t, Fig. 1, passed over the pitch-covered block and around 

 the cylinder, being rigidly soldered to the latter. The 

 whole arrangement can be neatly finished by smoothing 

 over with hot pitch. To this band may be fastened 

 rings for hanging a dead weight and for the suspension 

 of the machine itself by means of a cord. Insulated 

 wires connect the binding posts of the machine with 

 the "ticker" or recording device, Fig. 4. This con- 

 sists simply of a small electro magnet m, made by 

 wrapping the iron bolt with a small quantity of insulat- 

 ed magnet wire, and a bent strip of tin n for sounder, 

 which is regulated by the screw x. A single cell of 



ing device and dry cell, costs the makers a total cash 

 investment of 45 cents. 



