30  =Professor J. D. Everett’s Description of a Method 
In the physical department of meteorology the determina- 
tion of “date of phase” will furnish a measure of the precise 
amount of retardation which is caused by the sea, as well as 
by different kinds of soil. It is obvious that the interchange 
of heat between the soil and the air must have a tendency to 
retard the phases of temperature in the latter, since the soil is 
more slowly heated and more slowly cooled than the air above 
it; but I am not aware that comparison has ever been made 
between the retardations produced by different qualities of 
soil. 
Or again, if it be required to determine whether the changes 
of temperature in the sea precede or follow those of the air 
(a question which was recently discussed with regard to the 
sea on the coasts of Scotland), the present method will afford 
an easy solution. of the question. 
The laws which connect date of phase with extent of range 
also offer an interesting field of investigation. Generally 
speaking, the causes which retard the former diminish the 
latter. 
In the application of meteorology to agriculture, date of 
phase cannot, without serious error, be overlooked. The earli- 
ness of crops at one place, as compared with another, must 
necessarily depend upon this element as well as upon mean 
temperature and range, and it will be interesting to ascertain 
how much of the effect 1s due to each of these causes. 
I will not furthgr enlarge upon the importance of the ele- 
ments determined, as the design of the present paper is rather 
to show how the determination may be affected than to specu- 
late as to its ulterior uses. 
Concluding Note. 
The following theorem, which comprehends several of those 
above enunciated, will possess an interest for the mathematical 
reader. Let the expression for the mean temperature of the 
1 
wie part of a year be— 
Y=A,+A, sin (a+ E,)+ A, sin (20+ H,)+ ....+A*sin 
(na + E,) 
years of Adie’s Observations, as given in the “'Transactione of the Royal Society 
of Edinburgh,”—Epiror Edin. New Phil. Journal.) 
