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 comparing induced spark lengths from magneto and battery ignition systems with an earthed metal tube.
| Identifier | ExFiles\Box 61b\4\ scan0210 | |
| Date | 19th February 1925 guessed | |
| -2- Contd. II. With the tube earthed, the lengths of the induced sparks obtained were reduced to almost nothing, as shown :- Magneto wires sparking battery wires idle. No. Spark lengths. 1 .006" 2 .006" 3 .010" } INDUCED SPARKS ON B. I. GAPS. (EARTHED METAL TUBE). 4 .010" 5 .010" 6 .010" Battery wires sparking magneto wires idle. No. Spark lengths. 1 .004" 2 .004" 3 .006" } INDUCED SPARKS ON M.{Mr Moon / Mr Moore} I. GAPS. (EARTHED METAL TUBE). 4 .008" 5 .004" 6 With either or both ignitions working there was quite a marked difference, due to earthing the tube, in the characteristic of the main sparks, the effect on the sparks being that well known effect of the addition of a H.T. condenser in parallel with the H.T. supply. On the other hand, the act of earthing the tube did not impair the regularity of sparking on 6.5 mm, and on 5.5 mm. gaps for the battery and magneto ignitions respectively. In tests carried out some time ago, it was found that the H.T. sparks obtained from the old short coil were reduced considerably in spark length by enclosing the wires | ||