20 Professor J. D. Everett's Description of a Method 
the error to the deduced range will be upon the average the 
same in both cases.* 
The element of “ date,” which thus interferes with the de- 
termination of range from monthly means, is for its own sake 
well worthy of careful investigation ; but meteorologists 
generally content themselves with loose estimates of its 
amount, and I am not acquainted with any meteorological 
work which contains directions for computing it. 
The design of the present paper is to supply this deside- 
ratum,} by describing a convenient method of deriving both 
“range” and “ date of phase” from the mean temperatures of 
the twelve calendar months. I shall not enter into the 
mathematical investigation on which the method rests (for 
which I may refer to two papers, by Professor W. Thomson 
and the Author, read before the Royal Society of Edinburgh 
on the 30th April 1859), but shall confine myself to a brief 
account of the principle of procedure, with full details of its 
practical application. 
The method virtually consists in removing the irregularities 
which characterise the actual curve of temperature for any 
place, so as to obtain in its stead a regular curve which can 
be expressed by a simple mathematical formula. In the re- 
duced curves thus obtained for two places, we have a definite 
measure both of the interval of time by which the phases of 
temperature are on the whole earlier at one place than at the 
other, and of the annual range at each place, as deduced 
from a comparison of the warmer half of the year with the 
colder. 
* Jf the variations of temperature conformed to the simple curve of sines, 
the difference between the mean temperatures of two equal and opposite por- 
tions of the year, of given length, would vary directly as the difference between 
the temperatures of their respective centres. 
t [This cannot be called a desideratum, for the method here spoken of has 
been in familiar use among meteorologists for thirty years or more. It has 
been published in Kaimst’s Meteorology, is noticed by Sir John Herschel in the 
article “ Meteorology” in the Encyclopedia Britannica, and is specially adopted 
by Principal Forbes in his article on the climate of Edinburgh, in the last 
volume of the Transactions of the Royal Society of Edinburgh. These authors 
have fully adopted it, and pointed out the significance of the three constants 
for—l. Mean Temperature; 2. Range; 3. ‘“‘ Date of Phase.”—EpDITOR Ldin. 
N. Philos. Journal.| 
