122 Mr. J. Y. Buchanan. On Rapid Variations of [May 31, 



rises, falls, and remains stationary quite irregularly. On some days, 

 as on the 28th February, these irregularities are comparatively few ; 

 on others, as on the 1st and 2nd of March, they are numerous. The 

 largest rise or fall in twenty seconds is 0'5 C. From experiments in 

 t;alm air outside and in still air in a room we find that for this 

 thermometer to rise or fall 0'5 C. in twenty seconds the temperature 

 of the air around it must be from 2'25 C. to 4'65 C. hotter or 

 colder than the thermometer. Taking even the lowest of these 

 values, we see how great the possible error is in measuiing the 

 actual temperature of the air at any moment with a thermometer, and 

 the error is the greater the more sluggish the instrument is. In 

 Table IV the detailed observations are given for a few minutes on 

 the 26th February, when the temperature was changing very 

 rapidly. In the third and fourth columns the rise or fall of the 



Table IV. Temperature of the air at St. Moritz, observed at intervals 

 of twenty seconds. 



