The Rev. H. Llotd on the Meteorology of Ireland. 429 



DiuENAL Ranges of Temperature. 



Climatology depends upon the ranges of temperature (whether diurnal, 

 monthly, or annual), no less than upon mean values; and their investigation is 

 accordingly a necessary part of the present inquiry. In the present series of 

 observations, the diurnal ranges of temperature are given by means of the results 

 obtained with self registering thermometers. These results are the least satis- 

 factory portion of the whole series. It is well known that the ordinary self-regis- 

 tering thermometers are extremely apt to get out of order, the maximum by the 

 index becoming entangled in the merciuy, and the minimum by the distillation 

 of the spirit into the upper part of the tube ; and although the observers were 

 carefully instructed in the mode of remedying these derangements, no one (I 

 believe) who has handled such instruments will wonder that men previously 

 unaccustomed to them should have sometimes failed in what is in all cases a 

 somewhat delicate operation. The blanks in the Table of maximum temper- 

 ature at Buncrana and Killybegs, and those in the Table of minimum tem- 

 perature at Killybegs and Dunmore, are due to this cause. 



But there is another source of error affecting the maximum thermometer, 

 which it is still more difficult to avoid. If the instrument be exposed to the 

 influence of radiation for any portion of the day, however short, it will, from its 

 construction, retain the impression made upon it; and consequently, if the ab- 

 normal temperature to which it has been thus subjected exceed the greatest 

 temperature of the air in the day, an erroneous result will be recorded. The 

 difficulty of guarding thermometers completely from such influences is well 

 known ; and although some trouble was taken to insure this protection, the 

 observations themselves show that it was not effective at all the stations. I 

 have, accordingly, been compelled to reject a portion of the results obtained 

 with the maximum thermometer at Killough, Courtown, Kilrush, and Dunmore, 

 as defective from this cause. 



The results are given in the following Tables. Table viu. contains the 

 monthly means of the maximum temperature in each day ; Table ix. those of 

 the minimum temperature ; and Table x. the differences of the two preceding, 

 or the monthly means of the diurnal ranges. 



3 K 2 



