The Tasimeter and Magnetisation

Abstract

AFTER perusing an account, in a recent number of the Scientific American, of Edison's Tasimeter, it occurred to one of us to apply it to detect, and, if possible, to measure the elongation and shortening, which, as discovered by Joule, are produced in a bar of iron by magnetisation and demagnetisation. Accordingly to test whether the effect could be observed in this way, a rough specimen of the instrument was constructed, and with it some preliminary experiments made, an account of which may interest the readers of NATURE. A small cylinder, about half a centimetre in length and diameter, of the carbon used for Bunsen's cells, rested with its ends which were slightly rounded, in contact with two brass plates, one of which was fixed to a rigid upright attached to one end of the base of the instrument, while the other, resting with one end on the base, formed a spring, which in its normal position just touched the end of the carbon. A coil containing four layers of insulated wire, six turns to the layer, was wound round a tube ten centimetres long and eight millimetres in diameter, and fixed with its axis in line with that of the carbon cylinder. A piece of iron wire was then placed in the axis of the tube with one end resting against the spring, and the other in contact with the end of a screw working in a nut fixed to a rigid upright at the end of the base remote from the carbon. By means of this screw the pressure of the iron bar on the spring, and consequently of the spring on the carbon, could be varied at pleasure.