Morton-Wall: central claims
Note on scope: the project folder holds one file, a 623-page Google Books scan of the whole Journal of the Franklin Institute, Vol. LXI (Jan-June 1871). It contains two relevant articles: Edwin J. Houston, "On a New Connection for the Induction Coil" (PDF pp.594-596) and William H. Wahl, "A Large Induction Coil" (PDF pp.319-323) about Henry Morton's coil. The folder name "Morton-Wall" is read here as Morton and Wahl (an assumption). The text is readable (OCR good), so there is no source gap in the usual sense. Morton's own paper on secondary condensers (Journal Vol. LIII, April 1867, pp.256-260) is not in the folder but was found by the Investigator and read [read: research/files]; it already says a jar shortens the spark and greatly increases its brightness. What is missing from the folder: Wahl's promised later account of experiments with the Morton coil, and any later work by Houston on this connection (Houston's Jan 1876 and Houston and Thomson's Apr 1876 papers were found by the Investigator). Wahl's figures in this file were re-read from page images (the OCR text layer misreads fractions); the earlier '443 miles', '825 sq ft' and '14 sq ft' were OCR errors. Houston's stated aim (p.594) is 'increasing the quantity of the spark of the induction coil without greatly diminishing its length'. Houston's article gives no battery, primary current, dates, witnesses or measured values; everything about "quantity" is by eye.
- Connecting one pole of an induction coil's secondary to earth (a gas pipe) and the other to a large, imperfectly insulated conductor (a lecture table, which is in partial earth connection through gas and water pipes, not insulated) turns the spark thicker, shorter and silvery white, like a Leyden jar in the discharge path, while long sparks can be drawn from metal objects 8-9 ft away. (Houston, 1871; observed, not measured.)
- With the other pole on a stove system, sparks could be drawn from a small steam engine about 30 ft away and, in one instance, from a wire in a room below. (Houston 1871; the path to the engine is not described there; Houston's Jan 1876 account says the engine was also in metallic connection with the water-pipes, and describes the 1871 reach as 'any metallic objects in the neighborhood of the coil, and, indeed, in adjoining rooms'.)
- A large insulated conductor (tin stills on glass jars) on one pole, the other earthed, raises the "quantity" of the spark. With a separate insulated conductor on each pole (neither earthed), quantity rises but length falls; shrinking one conductor below about one square foot then restores a spark of about 5 in "without sensible diminution in quantity" from a coil rated at 6 in free-air. The five-inch result belongs to the two-conductor, neither-earthed case only. (Houston; "quantity" judged by eye.)
- Houston explains this as the large conductor allowing rapid discharge of the secondary and so rapid induction in it, as when a frictional machine's conductor is earthed, and proposes (untested) an insulated conductor of several hundred square feet on one pole with the other earthed as the maximum arrangement.
- Ritchie's coil for Morton (about 44 1/3 miles of secondary wire, 250 lb in all) gives 21 in sparks from three bichromate cells, and kept working for months, whereas a larger London coil (App's, for Pepper: 150 miles of wire, nearly a ton, 29 in from about sixty cells) soon failed. The contrast is 44 miles for 21 in against 150 miles for 29 in. (Wahl, a co-editor writing about his colleague's instrument.)
- The same coil with a Leyden jar or Morton's secondary condenser gives short, white, loud sparks (about 2 3/4 in with a 1 1/3 sq ft jar, 2 3/8 not fully excluded; 14 in with a 20-pane condenser), and coupling its halves for "quantity" shortens the spark to 12 in. (Wahl.) This is the same trade-off between spark length and quantity that Houston describes.