Chemical and Physical Notes \ 1 7 



temperature of the air is best shown by the curve drawn by a recording 

 thermometer of sufficient sensibility combined with a clock movement 

 of suitable velocity. Such an instrument draws a sinuous line which is 

 generally smooth during the night and serrated during the day. The 

 shape and the crowdedness of the teeth on the serrated daylight portion of 

 the line have a close connection with, and are to a certain extent an 

 indication of, the character of the existing weather. In general the 

 indented character of the daylight curve is an indication of the dis- 

 turbing influence of the sun on the equilibrium of the atmosphere, and 

 this continues just as long as he is above the horizon ; after sunset, the 

 atmosphere quickly reverts to a state of greater stability." 



It is only necessary to watch a thermometer during one 

 or two minutes to be convinced of the great variability of the 

 temperature of the air not only from one minute to another, 

 but almost from second to second. This is most easily and 

 most briefly shown by quoting the series of observations made 

 at St Moritz, in the Engadine, in February 1894. 



" In the winter of this year I revisited the Engadine, and stayed for 

 a fortnight at St Moritz. As the room which I occupied faced due north, 

 the window of it was convenient for making observations of the tempera- 

 ture of the air. From the 25th February to the 3rd March I made every 

 morning a series of observations of the temperature of the air, beginning 

 when there was just light enough to read the thermometer, and continuing 

 till between 8 and 9 o'clock in the morning. At first I took the tempera- 

 ture every minute, but finding the oscillations of temperature very great, 

 I reduced the intervals to twenty seconds, and sometimes to fifteen 

 seconds. To print the observations in extenso would occupy too much 

 space, but the striking features can be easily summarised. They are 

 given in Table XIX. Excepting on the 26th February, when it was 

 snowing all the morning, the observations embrace the interval of an 

 hour or an hour and a half after sunrise. The time was devoted entirely 

 to this object, and observations were made at as close dates as possible. 

 Working alone, an interval of twenty seconds is quite convenient ; shorter 

 intervals cause hurry. The time immediately following sunrise is when 

 one would expect the temperature of the air to rise continuously, if not 

 regularly ; but we see that so far from rising continuously and regularly 

 the thermometer rises, falls, and remains stationary quite irregularly. 

 On some days, as on the 28th February, these irregularities are com- 

 paratively few; on others, as on the ist and 2nd of March, they are 

 numerous. The largest rise or fall in twenty seconds is o'5 C. From 

 experiments in calm air outside and in still air in a room, we find that 

 for this thermometer to rise or fall o'5 C. in twenty seconds the tempera- 

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



