636 
LIEUT.-GENERAL R. STRACHEr ON HARACONIC ANALYSIS OF 
forms of the curves from which they were derived, this affords no true indication of the 
existence of distinct physical influences operating in recurring cycles of 24, 12 , 8 , and 
6 , corresponding to the four orders of components ; but that the results are, to a great 
extent, due to the particular form given to the analysis. 
The component of the first order represents a variation from the mean value, which 
is symmetrical on either side of the epoch of its maximum, and necessarily involves a 
negative departure from the mean, equal to a corresponding positive departure at the 
hour of maximum, and twelve hours distant from the maximum. 
As the diurnal curve of temperature is not symmetrical in relation to the mean 
value, the maximum day temperature being much more in excess of the mean than 
the minimum night temperature is below it, the first component, which is S 3 unmetrical 
in this respect, must be modified by the other components; and that of the second 
order, which has one of its maxima not far removed from the epoch of minimum of the 
first component, supplies the chief portion of the compensation necessary to correct the 
excess of that minimum over the true minimum. 
Further, from the character of the analysis, the third component will be zero when 
the diurnal curve is symmetrical, but with contrary signs on either side of the hours 
half-way between noon and midnight, that is when the length of the day and night 
are each 12 hours. Any departure from this equality will introduce a conq)onent of 
the third order ; with the result, that with a day shorter than 12 hours, one maximum 
phase will be between 6 a.m. and 6 p.m., and the other two in the hours before 6 a.m. 
and after 6 p.m. ; while with a day longer than 12 hours, two maxima will be between 
6 A.M. and G p.m., and the other in the hours after 6 p.m. and before G a.m. In 
the former case the two negative phases of the component will correspond with the 
reduced temperature in the morning and afternoon of the shorter day, and in the 
latter the two positive phases will correspond with the increased heat of the mornings 
and afternoons of the longer days. 
It will also be apparent that with a day of 8 hours, and a night of IG hours, or 
vice versd, the epochs of the third component would tend to synchronize with the 
duration of the night and day, and its amplitude might be expected to be then 
greater, which is seen to be the case. 
Analogous considerations will apply to the component of the fourth order. A 
positive maximum phase at or near midnight would give two maxima, near 6 a.m. 
and G p.m., respectively, corresponding to the long days in high latitudes in the 
summer, and also two negative minima at or near 9 a.m. and 3 a.m. respectively, 
corresponding to the short days in winter, in high latitudes. The Tables F and G 
both show P 4 , with a positive sign under the circumstances just stated. 
Again a negative phase at or near midnight would correspond to two negative 
phases at or near G a.m. and G p.m., respectively, which would correspond to the days 
and nights of nearly 12 hours in the lower latitudes and at the equinoxes, which con- 
