|
Date: |
|
Description: | R.W. PAUL, HATTON GARDEN, LONDON. (maker's trade name engraved in the ebonite top). RB4 (departmental number painted in white on three sides of the box0. MANU Robert,W. Paul circa 1895 114-115 Great Saffron Hil, London. E.C., England This is an R.W. Paul resistance box. It was used rather like a variable resistance. It is made of 16 German silver resistance coils , which are connected in series. German silver (approximately 60 percent), about 20 percent nickel, and about 20 percent zinc). Not to be confused with German standard silver, which is a silver alloy stamped usually 800 or 900 meanining 80 or 90% silver. When one of the keys on the top of the box is removed the value of that resistance is removed from the circuit. The total resistance of the box is 11,110 ohms. When the key marked INF. is removed this creates an open circuit, i.e. for all intents and purposes an infinite resistance and therefore effectively an on/off switch. The smaller value resistances in this instrument were particularly good as a variable shunts (low value bypass resistances) for altering the range of instruments such as galvanometers that detect changes in voltage. Although it was not an absolute resistance its values were of a sufficiently high standard for work in most experimental applications. However, they could only operate at low current ratings. By 1903 Paul's resistance boxes had chunky ebonite headed keys and the resistances were made from manganin an alloy of approximatey 83-85 % copper, 12 manganese and 2-4% nickel.. Manganin was invented by the English chemist Edward Weston (1850 -1936). | License: | http://www.hmag.gla.ac.uk/spirit/rights/ | Publisher: | Hunterian Museum and Art Gallery, University of Glasgow | Rights holder: | Hunterian Museum and Art Gallery, University of Glasgow | Subjects: | SCIENTIFIC COLLECTION : | Source: | Hunterian Museum | Creator: | Hunterian Museum and Art Gallery, University of Glasgow | Identifier: | http://www.huntsearch.gla.ac.uk/cgi-bin/... | Language: | en-GB | Go to resource |
|
|