502 



Journal of Agricultural Research voi. xvni, No. lo 



The following is the equation of the curve of figure 2 , which represents 

 the seasonal temperature change for Utah : 



T = 48.5— 20.91 cos 0— 1.28 cos 2 6> — 0.67 cos 3 + 



— 7.^7 sin ^ + 2.38 sin 2 ^ — 0.83 sin 3 6> + (3), 



or in terms of one trigonometric function only : 



T=48.5 — 22.2 cos {0— 19°— 54') — 2.70 cos 2(6*— 149°— 5') 



1.03 cos 3(<9-i7°-3') + 



(4), 



where T represents the temperature at the time 0. The first constant 

 in each of these equations (48.5) is the mean annual temperature for the 

 State, expressed in degrees Fahrenheit. 



In the last two columns of Table I it is shown that for the 30 county 

 seats of Utah the mean annual temperatures differ from the mean for 



IP 20 O ZO 10 £0 10 ZO 



JAN. FEB. MAR APffIL 



Fig. a. — Mean monthly temperatures for Utah. 



the State by from 0° to 10° F., with a mean departure of 4°, and that 

 the mean annual range for these towns differs from the State range 

 0° to 9°, with a mean departure of 4°. The first constant in the equa- 

 tion simply moves the graph as a whole up or down the page without 

 changing its shape. Inasmuch as the annual range in temperature — 

 the difference in temperature between summer and winter — is nearly 

 the same for all these county seats, making all their curves of approxi- 

 mately the same shape, the above equation can be used for any of Utah's 

 towns or any other place that has the same annual range by replacing 

 the first term by the mean annual temperature for the place in question. 

 To determine the mean daily temperature on April i for Salt Lake 

 City, change the date to degrees by dividing the number of days that 

 have elapsed since January i by 365 and multiply by 360, which gives 



