Chemical and Physical Notes 



81 



Edinburgh on September 16, 1894, during very fine anti- 

 cyclonic weather. All the afternoon the air was perfectly 

 calm. The smoke from chimneys went straight up and 

 indicated no horizontal component of motion. 



In the following table the " half-falls " for different initial 

 excesses at different times during the afternoon are given, 

 which show the extent of their agreement. The mean 

 "half-fall" is then converted into the term of cooling by 

 multiplying by -^^f. 



TABLE XII. 



This table shows well what great differences may exist in 

 the calmness of calm air. Nobody doubts that such motions 

 do occur ; otherwise it would be impossible for the permanent 

 difference of temperature which is found generally to exist at 

 different elevations in the atmosphere to be maintained ; and 

 it is interesting to have a means of gauging them. 



In order to obtain a standard of measurement, a number 

 of observations were made by moving the thermometer at 

 different velocities in the air of the room, and observing the 

 rates of cooling. Dealing only with low velocities it was found 

 that while in perfectly still air the term was 65 seconds; when 



B. 6 



