372 HUMPHREYS: DIURNAL VARIATIONS 



It was shown that for a function of r, the spherical modulus, 



V =— /pand V 2 = — /V + -— /p 2 . 

 dr dr 2 r dr 



For spherical coordinates, 



_ d , . d . dp . d . dp 



V = — / P -] r — + — I r — ; 



dr dd d9 d<? d<^ 



and the conjugate square of V was deduced by applying the for- 

 mula for multiplication, and expanding the resulting terms. 



METEOROLOGY. — On the diurnal variations of atmospheric 

 pressure. W. J. Humphreys, U. S. Weather Bureau. To 

 appear in full in the Bulletin of the Mount Weather Observa- 

 tory. 



It has been known for nearly two and a half centuries that there 

 are more or less regular daily variations in the height of the barome- 

 ter, culminating in two maxima and two minima during the course 

 of twenty-four hours; the maxima occurring at 10 o'clock, roughly, 

 forenoon and evening, the minima at 4 o'clock, roughly, afternoon 

 and morning. 



Some of the observed facts in regard to this twelve-hour cyclic 

 change of pressure are: (1) The amplitude is greatest in the 

 tropics and decreases towards the poles, approximately as the 

 square of the cosine of the latitude; (2) The amplitude is every- 

 where greatest at equinox and everywhere least at solstice; (5) 

 The amplitude is greater at perihelion than at aphelion; (4) 

 The amplitude is greater by day than at night; (5) The amplitude 

 is greatest on clear days and least on cloudy; (6) The day ampli- 

 tude is greater over land than over water; (7) The night ampli- 

 tude is greater over oceans than over continents; (8) Over the 

 tropical Pacific Ocean the forenoon barometric maximum is about 

 1 mm. above and the afternoon minimum 1 mm. below the general 

 average. 



Here and there through the voluminous literature on this meteor- 

 ological mystery one may find an attempt to explain its origin. 



