Joule (James, physicist, 1818-89) Autograph Letter signed to William Thomson, later Lord Kelvin, 3pp., 8vo, Scarborough, Yorkshire, 14th August 1876, on an experimental apparatus, "I wrote to Maxwell and am glad to hear that he is taking steps for determining the unit of resistance. Therefore I have altered the last paragraph in the proposed report report I sent you... . I wish you would try castor oil in your top. It would perhaps be a sort of 'half way house'. In using it for a resisting material for the vane under my ?dip circle I have found a very great advantage. It is far better than any other liquid I tried for bringing the instrument to rest. In the machine you saw, its use is essential; any other oil did not prevent grinding. But with castor oil there seems to be no abrasion whatever. In fact the oil which comes away is nearly colourless", and with a pen and ink sketch of a calorimeter", small tear along fold at tail, folds.