On the Daily Range of Atmospheric Temperature. ^77 



" On tlie Variations of tlie Daily Range of Atmospheric 

 Temperature as recorded at tlie Kew Observatorj^^^ By 

 Balfour Stewart^ LL.D._, F.R.S., Professor of Natural 

 Philosophy at Owens College^ Manchester. Beceived May 

 25, 1876^. 



1. There are reasons for supposing that differences of temperature in 

 the A'arious portions of our globe and of its atmosphere are, in whatever 

 manner these may be produced, the chief primary causes of meteorolo- 

 gical activity. Such differences of temperature produce differences of 

 atmospheric pressure, and these in their turn produce winds. 



Eor this reason the daily range of atmospheric temperature has been 

 chosen as an element which serves well, in many respects at least, to in- 

 dicate the varying meteorological activity of the place, and also because, 

 if it be found capable of indicating useful results, it has the advantage of 

 being observed with little labour, ^vhile the observations are compara- 

 tively easy of reduction. 



The records of the Kew Observatory have been chosen because there 

 the atmospheric temperature has been observed for a long series of years, 

 particular attention being paid to the construction and exposure of the 

 stand containing the thermometers t. Twenty-one years of these records 

 have been reduced, beginning with the year 1855, a year just precediug 

 the minimum of sun-spot activity, and ending with 1875, which may also 

 be reckoned a minimum sun-spot year. 



Two complete sun-spot periods are thus embraced in these obser- 

 vations. 



A. Annual Variation of Tenperature-JRange, 



2. It is already well known that the daily range of atmospheric tem- 

 perature is greatest in summer and least in winter. The following Table 

 exhibits the various monthl}^ means of the daily temperature-range : — 



* Read June 15, 1876. See ante, p. 156. 



t The writer is indebted to the kindness of the Kew Committee for giving him 

 access to the records of the maximum and minimum temperatures taken at the Kew 

 Observatory. 



