February, 1865.] The Freezing- Poifit of Mercury. 147 



These experiments still further confirmed his uncertainty as to the 

 true freezing-point of mercury, and he was at a loss to know how to 

 coiTect his thermometer-register. On the following day he continued 

 his experiments with frozen mercury, the lowest temperature during 

 the night having been — 39° ; and at 7 a m. his thermometers standing 

 thus: - 3(3°, - 90°, - 72°, - 34°, - 36°, - 36°, - 40°, - 42°. An 

 attempt to mold mercury into a bullet did not meet with success. The 

 temperature of the freezing mass now differed from what had appeared 

 on the previous day, and he began to question whether its repeated 

 freezing does not affect the case, or whether the discrepancies noted 

 had not arisen from some lack of watchfulness needed to prevent the 

 communicating of heat to the thermometers from his own person.* 

 He says: ''Why should I not be in doubt about the freezing-point of 

 mercury when masses freeze and little rain-drops of the same metal 

 from the same jar remain fluid ? Admitting that mercury freezes, by a 



* These notes of Hall's experiments may be compared with the following, to be found in the 

 " Results derived from the Arctic Expedition, 1875-'76" (Pariiameutary Paper C, 2176). Captain 

 Nares says, on p. 107 : 



"The spirit and mercury thermometers were fixed alongside one another in the same 

 screen, and, being read o^ every hour during the winter, were found to agree very well together 

 until the temperature fell to about — 44°, when, on the temperature reaching a certain point be- 

 tween —45° and — 46°.5, the mercury fell suddenly to a point in the tube Avhich would be about 

 equal to — 60° had the tube been graduated. 



"While in this state, the mercury could be easily tapped down to a lower point in the scale. 

 It appeared to be very brittle— that is, as the end of it reached the narrow passage leading to the 

 bull), small particles broke off and found their way through. The stream was not continuous. 



"When the thermometer was left <iuito sUU, no matter how cold the atmosphere was, the 

 mercury never sank lower in the tube than about — 60°. 



" When a thaw set in, the first effect was to melt the mercury remaining in the tube, which 

 fell into the bulb out of sight, the mercury in the bulb always taking a longer time and a higher 

 temperature before it became fluid. By the obser-v ations made, this temperature is about - 35°, 

 but length of time may affect the actual degree at which the mercury would become fluid. 



" Occasionally, when the mercury assumed the fluid state, the expansion was apparently a 

 sudden actiou, as the mercury in the tube of the maximum thermometer, lying in nearly a hori- 

 zontal position, was projected along the tube, and registered a much higher temperature than 

 that of the atmosphere ; thns, on February 22 the maximum thermometer registered a tempera- 

 ture of + 51°. 5, and on March 30, + 3^.0, botli readings being higher than the actual temperature 

 experienced." During the 24 hours preceding the first of these observations, the weather was 

 stormy, and the thermometer may have been shaken. 



