METEOROLOGY 377 



been corrected for the temperature of the mercury, the constant 

 error of the instrument, and the variation of the force of gravity 

 from the normal in latitude 45°. The reduction to sea-level, 

 on the other hand, has not been made; it amounts to I'l milli- 

 metre at an air temperature of - 10° Centigrade. 



The observations show that the pressure of the atmosphere is 

 throughout low, the mean for the ten months being 29 '07 inches 

 (738 '6 millimetres). It is lower in winter than in summer, July 

 having 28*86 inches (733 '1 millimetres), and December 29 '65 

 inches (753*3 millimetres), as the mean for the month, a difference 

 of 20*2 millimetres. The highest observation was 30*14 inches 

 (765*7 millimetres) on December 9, and the lowest 28*02 inches 

 (711*7 millimetres) on May 24, 1911; difference, 54 millimetres. 



Air Temperature and Thermometers. 



As has already been stated, minimum thermometers and mercury 

 sling thermometers were wanting. For the first six months only 

 toluene sling thermometers were used. Sling thermometers are 

 short, narrow glass thermometers, with a strong loop at the top; 

 before being read they are briskly swung round at the end of 

 a string about half a yard long, or in a special apparatus for the 

 purpose. The swinging brings the thermometer in contact with 

 a great volume of air, and it therefore gives the real temperature 

 of the air more readily than if it were hanging quietly in the 

 screen. 



From October 1 a mercury thermometer was also placed in the 

 screen, though only one divided to whole degrees; those divided to 

 fifths of a degree would, of course, have given a surer reading. But 

 it is evident, nevertheless, that the toluene thermometers used are 

 correct to less than half a degree (Centigrade), and even this 

 difference may no doubt be explained by one thermometer being 

 slung while the other was fixed. The observations are, therefore, 

 given without any corrections. Only at the end of December 

 was exclusive use made of mercury thermometers. The maximum 



VOL. II. 50 



