METEOROLOGY. 



287 



The mean annual atmospheric pressure is put down at 30.006 

 nches. This has been obtained from the mensual means derived from 

 he three daily readings. The diurnal mean calculated from the 

 lourly observations presents ^he following differences, which, if ap- 

 )lied^ would give the absolute mean for each month. 



It will be observed, on referring to the diurnal as well as annual 

 curves, that while each curve varies there is still, due allowance being 

 made for disturbing causes, a very apparent similarity, the evidence 

 of some regular moving influence, going and coming, present at one 

 season, absent at another, and returning again, and so on. These 

 phenomena bear the closest analogy with those observed at Algiers, 

 Oran, and other localities on the southern shores of the Mediterranean, 

 as established by A. Mitchell, A. M., M. D.* 



THERMOMETER. 



Like the barometer the thermometer reveals also some features of a 

 tropical rather than the temperate climate, to which latitudinally Sac- 

 ramento appertains. The mean monthly and annual temperatures, 

 as seen in the accompanying tables, are calculated, like those of the 

 barometer, from the daily observations made at 7 a. m., 2 p. m., and 

 9 p. m. This arithmetical mean is found to differ occasionally from 

 that obtained from the thermometrograph during the last two years. 

 The minimum temperature, as seen from the curves projected in the 

 chart of hourly observations, occurs between 4 and 5 a. m., and the 

 maximum about 3 p. m. Consequently the mean deduced from the 

 latter is generally minus that of the former. The following table 

 gives the correction to be applied in order to obtain the absolute mean: 



* British and Foreign Medico-Chirurgical Review, No. xxxiii, 1856. 



