METEOROLOGY. 



ABSTRACT OP OBSERVATIONS MADE DURING THE YEARS 185.1, 1854, AND 

 1855, AT SACRAMENTO, CALIFORNIA. 



BY THOMAS M. LOGAN, M. D. 



GENERAL REMARKS. 



Tlie following observations and tables have been carefully drawn 

 up and verified for future comparative reference. As the initiative of 

 a series of more comprehensive and perfect observations, wliich it is 

 proposed to prosecute for several successive years, they are now pre- 

 sented for record among the reports of the Smithsonian Institution. 

 The increasing rigor which advancing physical science exacts before 

 generalizations can be reliably deduced, especially requires the adop- 

 tion of such a course, in a new country like this, possessed as it is of 

 one of the most extraordinary climates known. In frequent instances 

 discrepancies will be found between the present tables and those pub- 

 lished^ in the reports for 1854, originating in errors of copy and ty- 

 pography, and which are now corrected. The barometric and thermo- 

 metric computations are the result of three daily observations. Prior 

 to April, 1854, they were made at 8 a. m., 3 p. m., and 10 p. m.; 

 since that date, at sunrise, 3 p. m., and 10 p. m. Henceforth they 

 will be continued, in accordance with the uniform system of observa- 

 tion adopted by the Smithsonian Institution, at 7 a. m., 2 p. m., and 

 9 p. m. The course of the wind was also noted three times a day, 

 corresponding with the above periods, as well as the state of the 

 weather in relation to clearness, cloudiness, and rain. By clear days, 

 is meant entirely clear — i. e., no clouds whatever being visible at the 

 time of observation ; by cloudy^ that some clouds were visible when 

 it did not rain ; and by rainy days, that more or less rain then fell 

 without reference to quantity. The dew-point was taken at the driest 

 time of the day only, (3 p. m.,) from July, 1854, to November, 

 1855, with Daniels' hygrometer ; since then, it has been calculated 

 from three daily observations with the wet and dry-bulb thermometer. 

 The three tables of hourly observations for twenty-four successive 

 hours, are the first of a series to be repeated four times every year, at 

 or about the period of the solstices and equinoxes, for the purpose of 

 determining the corrections to be applied, in order to render compar- 

 able with each other, the reeords made at different periods of the day. 

 It will be perceived, in these "term observations," that the horary- 

 oscillations of the barometer present in a marked degree the two di- 

 urnal maxima and minima which obtain within the tropics. From a 

 register kept with an extremely sensitive open-cistern barometer for 

 six months, from the 1st of April, 1855, to September following, in- 



