18 J. D. Everett on Reducing Observations of Temperature. 
y=A,+A,sin(e+E,) 
where A, denotes the mean temperature of the year, A, the 
amplitude, or greatest departure of the curve from the line of 
mean temperature, which will be the same above this line as 
below, and will therefore be equal to half the annual range, and 
, expresses the “date of phase” being greater in proportion 
as the phases are earlier. ‘The curve has one maximum and one 
minimum in the year; which are precisely half a year asunder, 
and exactly midway between these are the two points where the 
curve intersects the line of mean annual temperature, corres- 
ponding to these two days, one in Spring and the other in Au- 
tumn, whose temperatures are on the average the same as the 
mean of the year. 
ture being precisely similar to that which is below 
these halves being bisected symmetrically by the points of max: 
