RECORD AND DISCUSSION OF TEMPERATURES. 



Diurnal Variation. Before giving the table of the diurnal change of the atmo 

 spheric temperatures, it will be proper to remark that, astronomically, the upper 

 limb of the sun ceases to be visible at noon on Oct. 25th, and reappears at noon 

 Feb. 16th; between April 19th and Aug. 24th, the lower limb will continue above 

 the horizon without setting. On account of the considerable annual variation of 

 the temperature, the figures in the last vertical column of each month in the pre 

 ceding abstracts, headed &quot;mean,&quot; require a small correction for the effect of the 

 annual change during twenty-four hours; they will then represent the diurnal 

 variation for the middle of each month. Thus, for September, 1853, the effect of 

 the annual change during twenty-four hours is 0.50 decreasing, hence the maxi 

 mum corrections applied are 0.25 and +0.25 for l h - and 24 h - respectively; 

 and for the intermediate hours an aliquot part of this is applied, according to the 

 interval from noon, where the correction is zero. The following table presents the 

 summary of the diurnal variation for each month of the year; for the first five 

 months, the figures are the mean from two sets. The highest and lowest values, 

 for better distinction, are placed between parentheses. 



According to the preceding table, the epoch of the diurnal maximum temperature 

 occurs in the months of October and November (when the diurnal amplitude is a 

 minimum) about one hour before noon, and in April and May (when the diurnal 



