424 Mr. H. F. Blanford. The Diurnal Barometric 



specified, it is found that the second difference corresponding to 10 p.m., 

 with a positive sign, has a greater numerical value than either of 

 those preceding and following it, instead of an intermediate value, as 

 would be the case if the fall of temperature after sundown were 

 decreasing uniformly. In the following tables, the figures for Prague 

 and Batavia represent hundredths of a centigrade degree, those for 

 Calcutta hundredths of a Fahrenheit degree. The figures for 

 Calcutta are derived from only six years' autographic traces ; those 

 for Prague, apparently from eighteen or twenty years' observations 

 and traces ; and those for Batavia from ten years' readings of a 

 standard thermometer. No correction has been applied to the means 

 of the observations as recorded. 



Prague (summer). 



Hours, p.m 7 to 8 to 9 to 10 to 11 to mid. 



A T Change of temperature. . —115 —94 —85 —53 —44 

 A 3 Change of rate of fall . . +21+9 +32 +9 



Calcutta (year). 



Hours, p.m 5 to 6 to 7 to 8 to 9 to 10 to 11 to mid. 



A 1 Change of tempera- 

 ture -145 -248 -215 -111 -87 -61 -54 



A 2 Change of rate of 



fall -103 +33 +104 +24 +26 +7 



Batavia (year). 



Hours, p.m 5 to 6 to 7 to 8 to 9 to 10 to 11 to mid. 



A l Change of tempera- 

 ture -79 -76 -55 -41 -36 -27 -27 



Ac, Change of rate of 

 "fall +3 +21 +14 +5 +9 



The only further point of some significance, to which I have to draw 

 attention, is that the hour of the evening barometric maximum about 

 coincides with the time when the temperature curve ceases to be 

 strongly concave, and becomes nearly rectilinear, indicating a nearly 

 uniform rate of cooling from that time up to just before sunrise. 

 This fact suggests the possibility that the evening maximum of pres- 

 sure may be determined by the check in the descent of the cooling 

 and collapsing atmosphere which takes place from 6 or 7 p.m. to about 

 10 p.m.* But it is very probably combined with other elements, 



* This explanation was suggested by Kreil and Espy and also by myself in a 

 paper read before the Asiatic Society 4 of Bengal in 1876. On it Dr. Sprung 

 remarks : — " Es bleib f aber ganzlich unverstandlich, weshalb dieser Effect, sehon tun 

 10 Uhr abends, und nicht zur Zeit des Temperatur-Minimums gegen 6 Uhr 



