283 
In case thermograph records are not available the effective day- 
degrees can be determined approximately from maximum and minimum 
readings by the use of the following formule proposed by Dr. S. A. 
Forbes. 
Formulae for computing the average day-degrees above any given 
temperature, using the maximum temperature, and the minimum tem- 
peratures preceding and following it. 
a= Number of degrees that the first minimum is above or below 
the given temperature. ; 
b = Number of degrees that the second minimum is above or below 
the given temperature. 
c = Number of degrees that the maximum is above the given tem- 
perature. 
a —= Number of day-degrees above the given temperature. 
I. When both minima are at or above the given temperature, 
a+b+2c 
4 = ———___. 
4 
II. When the first minimum is below the given temperature, 
b+e (ee! 
4 = ——_ _ 4+ —__.. 
4 4(a+c) 
III. When the second minimum is below the given temperature, 
ate cy 
+= + — 
4 4(b-+c) 
IV. When both minima are below the given temperature, 
c? : c? 
“2 
4(a+c) 4(b+c) 
When the thermograph is used it should be kept correct by checking 
it up daily with the maximum and minimum thermometers, and the re- 
_ cording instrument should be kept in a place which has the same condi- 
tions as to temperature as the orchards to which the records are to be 
applied. It is very evident that the maximum and minimum readings 
taken in the heart of a city would not give readings that would apply 
to adjacent country districts. 
RELATION OF TEMPERATURE TO TIME WHEN LarvAE HIBERNATE 
In the spring, hibernating larve will begin to transform as soon as 
temperatures rise above 52° F., but after midsummer, soon after the 
temperatures begin to fall, maturing larve cease to transform long before 
the temperatures fall below the 52 point. 
