72 Lieut.-General R. Strachey. Harmonic Analysis [Mar. 2, 



2. Temperature at the Seven Observatories. 



The examination of the tables will show that in their main charac- 

 teristics the results closely resemble those for Greenwich, and it will 

 not be necessary to discuss them in any detail. 



The amplitude of the component of the first order is, however, in 

 all cases less than that observed at Greenwich, the lowest values 

 being those for Valencia and Falmouth, no doubt due to their posi- 

 tion on the sea coast, for which stations the means for the years are 

 2 0, 28 and 2 0, 35 compared with 5° "10 at Greenwich. 



The Kew values most resemble those at Greenwich, but the mean 

 maximum at Kew is more than 1° less, and the mean for the year \° 

 less. 



The mean values of fi x for the seven observatories lie between 205° 

 and 220°, that for Greenwich being 214°. The means of the summer 

 values are about 3° or 4° less than the mean of the year, and of the 

 winter values as much above it, as in the case of Greenwich. 



The amplitudes of the first components conform approximately, 

 but not so closely as at Greenwich, with the sine of the sun's 

 meridian altitude, but with a flattening of the curve in the summer 

 months, and a tendency at some of the stations to a maximum value 

 in May. 



The components 'of the second and third orders, beyond which the 

 analysis is not carried for these observatories, conform in all im- 

 portant respects to those for Greenwich, the numerical values of the 

 latter being, however, in all cases somewhat higher. The epochs of 

 maximum follow the same laws, with an increased divergence of the 

 summer epoch from that of the winter at the more northern stations. 



Making allowance for their smaller amplitude, the empirical 

 formulas expressing the mean values of the P 2 and P 3 components 

 differ little from those obtained for Greenwich. 



In order to test, and in some degree throw light on the character 

 and significance of the harmonic components of temperature that 

 have been under discussion, and bearing in mind that they 

 cannot be considered to represent separate effects of physical forces 

 operating at the assumed periods of the components, I have, at the 

 suggestion of Professor G. Darwin, calculated the harmonic com- 

 ponents that would produce a curve representing an intermittent 

 heating action such' as that of the sun, continued only during a 

 portion of the day, and commencing and ending abruptly at sunrise 

 and sunset. 



Such a procedure disregards all cooling effects, and only deals 

 with the sun's direct heating action, which I have assumed to be 

 proportional to the sine of his altitude. Also with a view of obtain- 



