172 TABLES OF TEMPEEATUEE. 



The exact relation which the mean, deduced from observations 

 made at various hours, bears to the mean temperature of the 

 twenty-four hours, is a desideratum for estimating comparatively 

 the respective temperatures of any two places mentioned in the 

 preceding table. Those marked Reduced and N. Y. have been 

 corrected to tiie true mean ; and from this the mean deduced 

 from the Daily Extremes differs very little. Besides these, the 

 means of observations taken at certain liours mentioned below 

 are also found to vary little from the true mean. An approxima- 

 tion to within a degree of this will be sufficiently near for pur- 

 poses relating to cultivation. 



The means of observations taken at — 



6 A.M. and 6 p.m. arerage about | of a degree below the mean. 



7 „ 7 „ „ ^ 



8 ., 8 „ „ -J „ ,, 



" )j y jj >> To T> 5> 



10 „ 10 ,, „ equal to the mean. 



7 A.M., 2 P.M., and 9 p.m. are hours which have been adopted 

 at a great number of places ; and these three daily observations 

 aflbrd a mean averaging scarcely | a degree above the mean of the 

 twenty-four hours. 



I may here remark, that with reference to cultivation, the 

 observations from thermometers indicating the maximum and 

 minimum daily temperatures are the most valuable. Although 

 hours may be selected which will give, as in the above cases, 

 the mean temperature, sufficiently near for all practical pur- 

 poses, yet fuom registering maximum and minimum thermome- 

 ters much more is obtained — the extremes are known, and from 

 these tlie mean maximum, mean minimum, and consequently the 

 average range of temperature, can be deduced. It is important 

 for gardeners to know all these particulars ; and hence desirable 

 that such instruments should be employed as will render it pos- 

 sible for them to do so. 



