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).
Technical table detailing measurements and observations for different annular gaps.
| Identifier | ExFiles\Box 4\5\ 05-page310 | |
| Date | 8th October 1924 | |
| X.4645. ANNULAR GAPS. 8.10.24. | 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 Out 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 discharge. | EPC. | ||