260 REPORT — 1875. 



subjected. When wires of gradually increasing thickness are used, the amount of 

 the elongation diminishes ; but the duration increases considerably, lasting fifteen 

 seconds with a steel wire from two to three tenths of an inch in diameter. 



2nd. At the moment that the expansion occurs, an actual increase in tempera- 

 ture takes place sufficiently large to cause the wire to glow again with a red heat. 

 It is very curious that this after-ylow has not been noticed long ago, for it is a very 

 conspicuous object in steel wires that have been raised to a white heat and allowed 

 to cool. 



3rd. The molecular change taking place during cooling is accompanied by a 

 series of ticking sounds like those produced by scraping the edge of a metal plate 

 with a jagged knife. 



4th. But the most interesting point remains to be noticed. This is the fact that 

 the critical temperature is precisely that at which iron and steel resume their pro- 

 perties as magnetic metals, a property they had lost when at a white heat. 



5th. Further, the molecular changes already noticed are coincident with the 

 alteration in the thermoelectric properties of iron discovered by Prof. Tait. It 

 appears, therefore, that this remarkable critical temperature of steel is intimately 

 connected with many different and important phenomena. Some light may thus 

 be obtained on the inner structure of a magnet and other obscure phenomena. 

 The author stated that he had brought forward the foregoing points in a research 

 that is now in progress, in the hope that he might have the benefit of suggestions 

 fi'om the eminent phj'sicists that were present. 



On Mechanical Self- Register imi Apparatus for Barometer, Thermometer, Itain- 

 and Wind-Gauges. By N. Lowejjthal Lonsdale. 



The author described (1) a glass pen, of the form of the Wiirtemberg siphon, 

 filled with clear lithographic ink, and marking on a prepared zinc plate or cylinder, 

 from which might be printed zincographically copies for distribution and com- 

 parison; (2) the gearing, the "tape" conue.xion instead of rack and pinion; and 

 (3j two .sensitive thermometers — one an iron tube 56 inches long (closed at one 

 end), filled with mercury, and an iion piston ground in at the open end: the 

 piston has a play of one inch between the freezing- and boiling-points ; but by 

 means of his gearing this inch can be augmented ad libitum, and in connexion with 

 the writing-apparatus would mark any fraction of Fahrenheit's degree. The other 

 thermometer is a hammered or drawn zinc rod, 13 feet 6 inches long. These ther- 

 mometers being fixed in the open air move an axis which penetrates the wall (or a 

 pane of glass); and fixed on the other end, in the 7-com, is an index, as also the 

 well-balanced registering-apparatus. 



Eain and velocity of wind are indicated by a governor and the above-mentioned 

 gearing ; and the direction of wind by an arm, in connexion with the vane-.'haft, 

 revolving lound a zinc cylinder. 



