26 



RECORD AND REDUCTION 



If we supply the constant term, and change the epoch from noon to midnight, as 

 in tlic above expression, the diurnal variation at Van Rensselaer Harbor has been 

 represented by 



t = _2°.01 + 1°.85 sin (9 + 244° 55') + 0°.08 sin (29 + 97°) + 0°.03 sin (39 + 308°), 



which is here added for comparison. 



In either expression, the constant term might be omitted, as not essential in the 

 inquiry of the diurnal fluctuation; or the values +2°.02 and — 2°. 20, which are 

 the true mean annual temperatures respectively, might be substituted in their place. 



The maximum and minimum value is given by the formula: — 



o = +2°.02 cos (0 + 252° 57') + 0°.51 cos (29 + 117°) + 0°.28 cos (39 + 251°). 



The following diagram (C) exhibits the diurnal variation during the whole 



year : — 



(C.) Diurnal Variation. 



Midn't 2" 



S u 10" Midii't 



Hourly Corrections for Periodic Variations. — Under this head, a number of tables 

 have been given by Prof. Guyot in his meteorological and physical tables, prepared 

 for the Smithsonian Institution. These tables furnish the means of correcting other 

 incomplete material at stations in the vicinity. A similar table was prepared by 

 me for Van Rensselaer Harbor. The following table for Port Kennedy is directly 

 derived from the values in Table II, in connection with Tables IV and IV (b). 

 For those hours requiring interpolation in the latter case, the small corrections for 

 the effect of the annual change during a day has again been deducted. 



