Donald MacFarlane to Faraday   19 November 1859

College Glasgow | Nov. 19, 1859

Sir

Prof. W. Thomson being at Edinburgh to day he desired me to send you an account of an experiment he made yesterday.

A flat ring, one half copper and the other zinc truly turned was insulated with its plane horizontal, a light aluminium index was suspended, by a fine glass fibre centrally over the ring, the index was connected by a fine platinum wire attached at its centre of motion, the wire hung vertically with its lower end in a dish of sulphuric acid and was thereby in communication with a conductor placed under the ring, the whole was inclosed in a case and the air kept artificially dry, the position of rest of the index was made to be exactly over the Copper & Zinc junction of the ring and the effect observed was, when care was taken that the glass of the enveloping case was completely diselectrified a slight charge of positive electricity communicated to the conductor below caused the index to be attracted by the copper, and a slight negative charge similarly applied caused the index to move towards the zinc.

I remain | Your Obedient Servant | D. M’Farlane