From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Test results on the effect of contact breaker speed on spark length.
| Identifier | WestWitteringFiles\D\January1920\ Scan38 | |
| Date | 21th September 1918 | |
| -2- Contd. B. Effect of contact breaker speed on length of spark. Coil. R.R. standard. Spark Gap. Platinum point gap as previously used for various spark tests. (a) The high tension cable (1 1/4 feet long) from coil was connected to spark gap, and the greatest gap to permit of even spark was measured at various speed from 100 - 1500 R.P.M. :- Running current(amps) | 1.35 | 1.27 | 1.20 | 1.13 | 1.07 | .97 | .86 | .78 | .70 | .62 | .57 Speed (RPM) | 100 | 200 | 300 | 400 | 500 | 650 | 850 | 1000| 1150| 1350| 1510 Gap.(inches) | .500 | .520 | .540 | .550 | +562 | .570| .575| .562| .520| .462| .430 | ||