Art. XLVIL.—Note on a supposed Heat-effect.

By J. S. S. Cooper, M.A., B.Sc.

[Read before the Otago Institute, 13th October, 1903.]

It is a common belief among blacksmiths that if a bar of iron with one end red-hot have this hot end plunged into water the cool end grows suddenly hotter. The effect is common to all metals, and is very striking if the cooler end be held in the hand until just uncomfortably hot.

To test if there were any real increase of temperature, or if it were merely an illusion, a brass bar was taken, .6 cm. in diameter, and one end was turned at a right angle so as to dip easily in water. 19 cm. from this end a hole was drilled in the bar, and a copper-german-silver thermo-electric couple was soldered in. The end of the bar was heated over the flame of an oil-lamp with a chimney. This proved a steady source of heat when carefully shielded from draughts. The heating was continued for half an hour, when the deflection of the galvanometer was steady. The hot end was then plunged in cold water (about 7°C.). In about thirty seconds the deflection began to fall, and continued to do so steadily. This proves that no real rise in temperature takes place such as could affect the senses.

The effect observed muse therefore be due to the continued advance of the ordinary heat-wave along the bar after cooling the end, and partly to the unconscious disappointment of the mind on failing to experience a sudden cooling

My thanks are due to Professor Shand, of the Otago University, for his courtesy in allowing me to use his laboratory on all occasions.