162 



Mr J. D. FORBES on the Horary Oscillations 



7. The influence of the seasons upon the horary oscillation 

 is an important inquiry ; and considerable uncertainty prevails 

 in the best observations. With regard to the hour, we find the 

 duration both of the morning and evening osciUation is greater in 

 spring and summer than in autumn and winter ; 8 or half-past 

 8 A. M. and 10 p. M. being the critical hours at the former period, 

 and 10 A. M. and 8 p. M. at the latter. With regard to the vari- 

 able amount, if we take advantage of the double hours of obser- 

 vation, and select the actual maxima, we shall find the following 

 amounts of oscillation : 



We thus see that both the morning and evening tide exhibits 

 the same order of decrease through the seasons, descending in 

 whiter, to a very minute amount. 



If we employ the fixed hours of 10 A. M. and 10 P. M. for the 

 maxima, we shall find the oscillation at a maximum in spring and 

 autumn, lower in summer, and the decided minimum in winter. 

 This agrees perfectly with the results of the observations made 

 at the apartments of the Royal Society, in London, which I 

 have collected from the Philosophical Transactions for the last 

 four years, during which the meteorological register has been con- 

 ducted on a much improved plan. 



