350 Sir D. Brewster on the Law of Daily Temperature. 



Hence it appears that the homonymous hours of mean 

 temperature are 4 h. a.m. and 4 h. p.m., and 10 h. a.m. and 

 10 h. p.m., the one differing only 5-100ths, and the other only 

 8-100ths of a degree of Fahrenheit from the mean annual tem- 

 perature ; while the maximum deviation, exactly as at Inver- 

 ness, occurs at 1 h. a.m. and 1 h. p.m., and at 7 h. a.m. and 

 7 h. p.m., amounting at Rothesay to + 0*56 and — 0*49, and 

 at Inverness to - 55, an agreement so remarkable that it can- 

 not but surprise us. 



The following table exhibits the difference between the 

 temperatures of each hour of the day, and the mean annual 

 temperature. 



As Inverness is colder in the morning than Leith, so Rothe- 

 say is slightly colder than Inverness, from 1 h. a.m. till 4 h. 

 a.m., then becomes slightly warmer till 1 h. p.m., from which 

 time it continues colder till 12 at night. 



With such a valuable series of observations as those at Rothe- 

 say, it became an object of great interest to ascertain the rela- 

 tion of the curve of annual temperature to the parabola. Before 

 we saw these observations we intimated to Mr. Thorn our con- 

 viction that the curve would deviate more from the parabola 

 than that at Leith, owing to the form of the visible horizon at 

 Rothesay being so different from the open horizon at Leith. 

 If a hill rises to the north of the place of observation, by which 

 the sun's rays are never obstructed, it can exercise little or no 

 influence on the thermometer ; but if one or more hills obstruct 

 the sun's rays after he has risen above the true horizon, that 

 obstruction must affect the temperature of the place of obser- 

 vation at the hours corresponding with the azimuth of the bill. 

 That this cause has operated at Rothesay will be seen from 

 the following table containing the observed temperatures, and 

 those calculated upon the supposition that the branches of the 

 curve are parabolic : — 



