468 



of a rough approximation to either the time of the maximum or minimum or to the amplitude. The 

 rise during the day may be traced from October to February, perhaps to March. 



The mean obtained from combining the eight dark months spent by the " Discovery " in the Antarctic 

 regions is shown in the diagram, fig. 3. 



6A.M. Noon 6P.M. 



Vertical Scale ^in. to iF. 

 Fig. 3. 



The maximum occurs at 4 a.m., the minimum at 10 p.m., but there is a secondary minimum at noon. 

 The difference between the highest and lowest temperatures is considerable, amounting to about 1 F., but 

 to what extent this curve is indebted to chance values and how far it represents a real phenomenon, it is 

 difficult to say. 



It is hard to believe that the rapid rise from 2 to .4 a.m. has any physical cause, but, on the other 

 hand, one can hardly doubt that the temperature is generally lower in the evening, or, since the word 

 can have no meaning in a place and time where the sun never appears, perhaps we should say lower from 

 8 p.m. to 2 a.m. than from 4 a.m. to 4 p.m. 



Every change in the height of the barometer produces a change in the temperature, for dynamic heating 

 or cooling of the air is produced by a change of pressure, no matter how that change is brought about. 

 We are too apt to consider a rising or sinking air current as the only natural cause of dynamic cooling or 

 heating, but, of course, the passage of air horizontally between two places under different pressure is 

 equally efficacious. The daily oscillation of the barometer, whether we consider the 12- or the 24-hour 

 period, inevitably produces a corresponding change in the temperature, although the converse of this is 

 not necessarily true. It is of . no consequence for this result how the barometric oscillation may be 

 produced, ceteris paribu.", a rise of temperature of 0- 5 F. accompanies a rise of O'lO inch of pressure, and 

 even though the actual rise may not occur, since some other more powerful cause may be producing a fall 

 of temperature, yet it is safe to say that, given the barometric rise, the temperature must be higher than 

 it would have been had no increase of barometric pressure occurred. Possibly, therefore, the 12-hour 

 period of the temperature may be a consequence rather than a cause of the pressure variation, but in this 

 particular instance I doubt the existence of any real temperature variation with the daily or half-daily 

 period during the winter. 



Observations with a black bulb thermometer in vacua are, unfortunately, not of great scientific value, 

 for it appears to be impossible to make two thermometers which will read alike, and it is most likely that 

 the reading of the same thermometer will vary with age. Under these circumstances, readings are not 

 comparable one with another. Indeed, this is evident from the above short table, for the size of the 

 bulb has in general made a difference of 20 F. in the monthly averages. But notwithstanding this, the 

 series of observations commencing on September 8 and ending in the beginning of April, 1903, are well 

 worth all the trouble expended on taking them, for they show the great permeability of the air to 

 radiation. 



