OF PERIODIC PHENOMENA. 347 



But then, to insure the correctness of this state- 

 ment, we must make our observations wherever 

 we can, as in the instance of plants we readily may 

 do, upon the same individuals. For though all are 

 equally subject to seasonal influence, there is a dif- 

 ference in individual temperament, which causes 

 some to be much sooner impressed by this influ- 

 ence, and to have their development proportiona- 

 bly accelerated. To this subject, however, we shall 

 have occasion to revert presently. 



(10.) Taking into consideration all that has been 

 above stated, it appears that the naturalist or the 

 botanist who wishes to determine the date of oc- 

 currence of any natural phenomena connected with 

 his particular studies, even in reference to a given 

 locality, must extend his observations over a con- 

 siderable number of years to obtain the mean time, 

 which is what he should always inquire after. It 

 should be remembered that there is a mean time for 

 the return of every phenomenon which is regulated 

 by time at all, however great may be the depar- 

 ture from it in particular instances. And the ob- 

 server's object should be to endeavour to find this 

 mean, by repeating his observations through such a 

 number of successive seasons as may insure com- 

 prising within the period seasons of as varying a 

 character as ever occur in that particular climate. 

 When the mean is ascertained,* it will be interest- 



* It must be borne in mind that the true mean of several dates 

 is not the mean of the extremes) but the mean of all the dates, 

 ascertained by adding the whole together, and dividing by the 

 exact number to which they amount. 



