518 REPORT— 1889. 



direction of the current, ■wliicli is with tlie motion of the flame, shows that at the 

 hot junction the current is from ' metal B ' to ' metal A .' 



An apparatus was exhibited, which contained a number of circular turns of 

 iron wire whicli could be continuously' heated in four places by the rotation of 

 four gas flames (fed from a central gas pipe and supported by cross pipes pivoted 

 at the centre). These flames were rotated by clockworli attached to the apparatus,, 

 the speed of which could be regulated by movable vanes so as to obtain the best 

 eflect. 



A detailed account of the phenomenon was published by the author in the 

 * Proceedings of the Royal Dublin Society' (March 1886). 



5. On Eecalescence in Iron. By Professor Barrett. 

 When an iron or steel wire is raised to a white heat and allowed to cool, it 

 obeys the ordinary law of cooling until it reaches a point near obscurity. At this 

 point, a temperature of between 700° and 800° C, the temperature suddenly rises, 

 and the wire glows again to a red heat. This phenomenon, known as recalescence, 

 was described by the author at the British Association meeting in Bradford six- 

 teen years ago. During the heating of the wire a reverse action occurs ; the tem- 

 perature momentarily ceases to rise, and even a fall of temperature occurs at the 

 same critical point. This critical temperature is associated with numerous other 

 phenomena which are found to take place in iron and steel. In 1869 Mr. Gore 

 discovered that, on cooling, iron wire momentarily elongated at this temperature ; 

 the reverse action, or contraction on heating, was found by the author in 1873, and 

 also that it is at this temperature iron by the action of heat loses its magnetic 

 properties. Further, a curious crepitating sound occurs at this critical temperature, 

 indicating some alteration of structure. Here, too, occurs the curious change in 

 the thermoelectric properties of iron discovered by Professor Tait ; and associated 

 ■with this critical point is the interesting discovery made by Mr. Trouton and 

 described in the preceding paper. Subsequent investigations, both on the Con- 

 tinent and in America, have shown that at this temperature many other important 

 changes in the physical and mechanical properties of steel occur, some of which 

 were described by Professor Boberts-Austen in his recent lecture before the Asso- 

 ciation. Mr. Tomlinson in London, and Mr. Newall at Cambridge, and recently 

 Dr. Hopkinson, have also given this subject a great deal of attention, and have 

 added much to our knowledge of recalescence and its associated phenomena. The 

 bibUograpby of the subject and the probable causes of the phenomenon will be con- 

 tained in the report of a Committee of the British Association, consisting of 

 Professor Fitzgerald, Mr. Newall, Mr. Trouton, and the author, which it is proposed 

 to present to the meeting next year. The present paper is presented more with the 

 object of eliciting discussion on this interesting phenomenon. 



6. The Cardium, illustrating the true nature of Prime Movers. 



By J. Gamgee. 



7. An Experiment in Colour-blindness.^ By J. Spiller, F.C.S. 



Before proceeding to describe his experiment, Mr. Spiller mentioned that he 

 had good proof of his being blessed with the possession of a normal sight, for in the 

 course of a long experience with coal-tar colours, and having frequent occasion to 

 compare observations in regard to slight differences of tint with six colleagues, he 

 had never perceptibly deviated fi-oni the consensus of the laboratory staflP, and might 

 fairly claim to be reliable on this score. He said that the examination of several 

 colour-blind persons had convinced him of the practical value of a compound tassel 

 of green and grey silk as a prelimmary indicator of defective colour vision. He 

 felt desirous of trying an experiment to see whether it was possible by the admini- 

 stration of a small dose of sautonine to realise the imperfections of vision which 



» Printed iti extenso in the Photograjihic News, September 20, 1889. 



