492 Tra?isactions. — Chemistry and Physics. 



which a spectrum-analysis vacuum-tube is used. A condenser 

 made of a slab of the kauri-cjum 1-38 cm. thick was compared 

 with one made of a slab of vulcanite 0-73 cm. thick. Wiih 

 the utmost care it was found impossible to obtain concordant 

 results. The value of the specific inductive capacity appears 

 to lie between 39 and 4-3, if the S.I.C. of the vulcanite in 

 question be taken as 3'15. 



The experiments were begun in 1899, but were mainly 

 carried out at Canterbury College in 1900. 



Art. XLVIL-:— A^o^e on a supposed Heat-effect. 



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



[Read before the Otago Institute, 23th 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, -Gem. 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 must therefore be due to tiic 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 labora- 

 torv on all occasions. 



