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).
Table of measurements and observations for different annular gaps, detailing spindle and hole diameters and the resulting coronal discharge.
| Identifier | WestWitteringFiles\M\2October1924-December1924\ Scan86 | |
| Date | 8th October 1924 | |
| - 32 - 8.10.24. X.4645. ANNULAR GAPS. | Gap particulars. | Spindle dia.(a) (mm.) | Spindle dia.(a) (inches) | Hole dia. (b) (mm.) | Hole dia. (b) (inches) | Gap (mm) b-a/2 | b/a | a/b | Remarks. | |---|---|---|---|---|---|---|---|---| | M.L. Gap originally. | 1.3 | .051 | 6.42 | .253 | 2.56 | 5.01 | 20 | Invisible but audible coronal discharge. | | Lucas gap originally. | 1.85 | .073 | 8.85 | .348 | 3.5 | 4.78 | 21 | Visible and audible coronal discharge. | | Lucas gap Our set A.{Mr Adams} (std). | 2.21 | .087 | 8.25 | .325 | 3.02 | 3.74 | 27 | Invisible but audible coronal discharge. | | Lucas gap Our set B. | 2.54 | .100 | 7.95 | .312 | 2.70 | 3.12 | 32 | Ditto. | | Lucas gap Our set C. | 3.17 | .125 | 7.95 | .312 | 2.39 | 2.50 | 40 | Very slight audible discharg | EPC. | ||