MADE AT BRUNSWICK, MAINE. 



31 



Diurnal Range of Temperature. 



The monthly mean value of the diurnal range may be obtained from the observed 

 differences at 7 A. M. and at 1 P. M. by multiplication with a factor derived from 

 the two Toronto series (reductions by Prof. Dove and Capt. Lefroy) and the Mon- 

 treal series of hourly observations given in the meteorological and physical tables 

 by Prof. Guyot, Smithsonian Miscellaneous Collection. 





observed 

 difference. 



Factor. 



Diurnal 

 range. 





Observed 

 difference. 



Factor. 



Binrnal 



January .... 



11°.4 



1.2 



13=. 7 



July .... 



11°.9 



1.7 



20°.2 



February 



12.7 



1.2 



15.2 



August .... 



12.7 



1.5 



19.1 



March .... 



12.3 



1.3 



16.0 



September 



13.4 



1.3 



17.4 



April .... 



11.2 



1.4 



15.7 



October .... 



12.5 



1.2 



15.0 ' 



May .... 



11.8 



1.5 



17.7 



November 



9.5 



1.2 



11.4 



June .... 



11.5 



1.6 



18.4 



December 



9.8 



1.2 



11.8 



Mean annual value of diurnal range 



16°.0. 







The diurnal fluctuation reaches" a maximum value in July, range 20°. 2, and 

 attains a minimum value in November, range 11°. 4.^ 



Annual Fluctuation of the Temperature. 

 The monthly mean temperatures (from 51 years), given in Table III, furnish 

 the following average values for the seasons and year ; to these were added for 

 comparison the corresponding values from a series extending over 22 years, observed 

 at Fort Preble, near Portland (latitude 43° 39', longitude 70° 13'), taken from the 

 Army Meteorological Register, 1855. It wiU be seen that the agreement in the 

 observed temperatures is quite close. 



Mean temperature of spring 

 " " of summer 



" " of autumn 



" " of winter 



" " of year 



Principally on account of the generalization of results from various stations and 

 the Necessity of contracting the bulky material of meteorology into a more manage- 

 able form, the periodic fluctuations are now generally expressed in Bessel's circular 

 function.^ A strict application of these formulae demands, for the annual fluctuation, 

 months of equal length ; the resulting mean temperatures of the calendar months 

 require, therefore, a correction for inequality. 



The length of the tropical year is 365.25 days, hence the length of an average 

 month 30.44 days. For complete quadriennia, or for a long series of years, we have 

 the following simple rule : Cast into February .56 of the last day of January, then 

 include with February the first and .62 of the second of March, with March the 

 first and .06 of the second oi April, with April the first and .50 of the second of 



Brunswick. 



Fort Preble. 



.■ . . . 42°. 26 Fahr. 



42°.n Fahr. 



. 65.11 



65.91 



. 47.59 



48.16 



. 22.63 



24.70 



. 44.40 



45.38 



1 These values for diurnal range perhaps are too large, and should be considered only as approxi- 

 mations ; possibly the thermometer may have been influenced by radiation. 

 ^ See U. S. Coast Survey Report for 1862, Appendix No.22. 



