Length of spark | 3/8 inch | 1/2 inch | 1 inch | 2 inches ------------------------------------------------------------------------ Size of bobbin | 2-1/8 × | 2-1/2 × | 3 × 3/8 | 4 × 2-3/4 × ends | 1-1/4 | 5/16 | | 3/8 ------------------------------------------------------------------------ Length of bobbin | 4 | 5-1/2 | 6-1/2 | 6-1/2 ------------------------------------------------------------------------ Length and | 4-1/4 × | 6 × 5/8 | 6-1/2 × 3/4 | ---- diameter of core | 7/16 | | | ------------------------------------------------------------------------ Size of base | 7-1/4 × | 9 × 5 × 2 | 14-1/2 × | 12 × 7-1/2 × | 3-1/4 × | | 6 × | 3-1/4 | 1-1/2 | | 1-3/4 | ------------------------------------------------------------------------ Size of tinfoil | 4 × 2 | 5-1/2 × | 6 × 4 | 6 × 6 sheets | | 3-1/4 | | ------------------------------------------------------------------------ Number of tinfoil| 36 | 40 | 40 | 60 sheets | | | | ------------------------------------------------------------------------ Size of paper | 5 × 3 | 6-1/2 × | 9 × 5 | ---- sheets | | 4-1/4 | | ------------------------------------------------------------------------ Primary coil | No. 18 | No. 18 |2 layers No. | 2 layers 14 | | |16, silk | B. W. G. silk | | |covered. | covered. ------------------------------------------------------------------------ Secondary coil | 3/4 lb. | 1 lb. | 1-1/4 lbs. | 2-1/2 lbs. | No. 40 | No. 40 | No. 38 | No. 36 ------------------------------------------------------------------------ TABLE OF SPARKING DISTANCES IN AIR.[13] | Distance. Volts. | (Inches.) ------------------------- 5000 | .225 10000 | .47 20000 | 1.00 30000 | 1.625 35000 | 2.00 45000 | 2.95 60000 | 4.65 70000 | 4.85 80000 | 7.1 100000 | 9.6 130000 | 12.95 150000 | 15.00 =Points Relating to Ignition Coils.=--1. Most ignition induction coils or “spark coils” as they are called, have terminals marked “battery,” “ground,” etc., and to short circuit the timer for the purpose of testing the vibrator, it is only necessary to bridge with a screw driver from the “battery” binding post to the “ground” binding post. 2. In adjusting the vibrator of an ignition coil, the latter should not require over one-half ampere of current.