112 Mr. Herbert Tomlinson on 



at any point of any of several subsequent trials which were 

 made. The next consideration was, Was the alternate darken- 

 ing and reglowing a subjective sensation*? The poker was 

 reheated, and after having been firmly fixed was watched 

 whilst cooling. As soon as the preliminary darkening ap- 

 peared, the head of the observer was turned slightly and 

 instantly brought back again. The whole operation of turn- 

 ing the head away and back again certainly did not occupy 

 more than a fraction of a second, and yet the metal shone out 

 quite clearly again. Closing and opening the eyes as quickly 

 as possible had a similar effect. No doubt such an instance 

 of subjective sensation is well known to physiologists, but it 

 has given the author a lesson which he will not readily forget 

 respecting the danger of trusting to mere sensationf. 



Several other attempts were made with bars and wires of 

 iron and steel ; and in the case of certain wires there seemed 

 evidence of more than one real reglow. In face, however, 

 of the warning given by the above experiment, the author 

 prefers to leave the point still open until he has completed 

 some calorimetric observations which he has in view. 



Experiment III. — A flat iron bar, 60 centim. long, 1*5 

 centim. broad, and 2 millim. thick, was heated at one end to a 

 very bright red, and observed when cooling in a dark room ; 

 a reglow occurred at a very high temperature J. The bar was 

 again heated, and whilst in the fire was bent as in fig. 2 ; it 



Fig. 2. 



was then kept in the fire a short time longer, and afterwards 

 removed. At first all the bar from A to E appeared to be of 

 the same temperature ; but presently a delicate cloud appeared 

 on the portion BC, which probably might have escaped notice 



* This was suggested by Mr. Burton at the Meeting of the Physical 

 Society at which the paper was read; the author feels much indebted 

 to Mr. Burton for the suggestion. 



f Possibly the intensity of the apparent reglow will be found to differ 

 with different individuals, and even to vary with the state of health at 

 the time. To the author the phenomenon was very striking. 



\ Considerably above dull red. 



