| Name and Model Number | "The Electrician" PRACTICAL WIRELESS SLIDE RULE |
| Country of Origin | England |
| Date of Manufacture | est. 1911 |
| Front Scales | Upper stock: Frequency per 1/1000 sec Wavelength in 1000 feet Wavelength in 1000 metres. Labelled C but in traditional A position. Red circled gauge marks ‘A and ‘B’ the latter at 2pi used for reading results. Slider: Wavelength – in 1000 metres labelled D to match C. Capacitance in Micromicrofarads x 100 = 90 cms Micromicrofarads in 100 cms Lower stock: Inductance in Microhenries x 10 20 cm scale. |
| Back Scales | No scales. ‘Instructions for Use.’ Various equations. Tables for wavelength conversion, dielectric constants and spark gap length/voltage. |
| Scale Length | 19.9 cm, with overall size 25.2 cm x 6.8 cm |
| Type of Rule | Slide Rule |
| Construction | Coated stiff cardboard |
| Area of Use | Electrical |
| Comment | 1) Electrical – L, C, wavelength and frequency for tuned circuits in spark gap transmitters used in wireless telegraphy.
Instructions on reverse note that the C and D scales can also be used for ordinary calculating. 2)The designer Henry Richard Belcher-Hickman M.A. M.B. is well documented as working in medicine. His electrical interests are described in V J Phillips ‘Early radio wave detectors’, 1978, p.199. 3)An owner’s name ‘Percival J. Parmiter’ is handwritten on reverse of slider. A person of this name ‘P. J. Parminter’ (sic) is on record in Gamage’s ‘Directory of Amateur Wireless Stations’ 1913 as operating a 35W transmitter in Bournemouth with call letters PXH. He presented talks on wireless telegraphy and other related subjects at the Bournemouth Natural History Society. |
| Rarity | RRR |
| Donor | Collection of David Walker, Huddersfield, UK |
| Match Number | 401 |
| Thumbnail (Click Picture for Details) |  |
| In conjunction with our 'donors' we assign a rarity rating to each item, based on the system devised by Herman van Herwijnen |
| (1929 - 2004), renowned Dutch collector, author, and creator of Herman's Archive, a collection of 5,000 slide rule images on CD. |
| • RR = Rare - 1 of 25 collectors has one; it may take a year to find an example in the marketplace. |
| • RRR = Very Rare - only a few known to collectors; may be several years before it comes up for sale. |
| • RRRR = Extremely Rare - a museum piece; unlikely that an example will come up for sale. |