﻿1848. METEOROLOGICAL SPECULATIONS. 6()6 



ing to find a reason for the ease with which at 

 some periods of arctic discovery navigators were 

 able to penetrate early in the summer into sounds 

 which subsequent adventurers could not approach, 

 and to connect such facts with the fate of the Dis- 

 covery ships. But neither the periods assigned, 

 nor the facts adduced to prove them by different 

 writers, have been presented in such a shape as to 

 carry conviction with them, until very recently. 

 Mr. Glaisher, in a paper published in the Philo- 

 sophical Transactions for 1850, has shown, from 

 eighty years' observations in London and at Green- 

 wich, that groups of warm years alternate with 

 groups of cold ones, in such a way as to render it 

 most probable that the mean annual temperatures 

 rise and fall in a series of eliptical curves, which 

 correspond to periods of about fourteen years ; 

 though local or casual disturbing forces cause the 

 means of particular years to rise above the curve 

 or fall below it. 



The same laws doubtless operate in North Ame- 

 rica, producing a similar gradual increase and sub- 

 sequent decrease of mean heat, in a series of years, 

 though the summits of the curves are not likely to 

 be coincident with, and are very probably opposed 

 to, those of Europe; since the atmospherical currents 

 from the south, which for a period raise the annual 

 temperature of England, must be counterbalanced 



