32 REPORT OF THE SECRETARY. 



The observations at Marietta, Ohio, extend from 1817 to 1823, 

 by Mr. Joseph Wood, and from 1826 to 1859, inclusive, by Dr. S. P. 

 Hildreth, the whole presenting an almost unbroken series of 40 

 years. Marietta, the oldest town in the State of Ohio, is situated at 

 the junction of the Muskingum and Ohio rivers, in latitude 39° 25', 

 longitude 81° 29' west, about 580 feet above tide-water. 



The registers embrace records of temperature, wind, pressure of 

 the atmosphere, face of the sky, cloudiness, and precipitation in snow 

 and rain. The observations of Mr. Wood were made at sunrise, 2 

 p. m. and sunset, and by Dr. Hildreth generally at G a. m., 2 and 9 

 p. m., in summer, and 7 a. m., 2 and 9 p.m., in winter. Deviations 

 in both series from these hours are noted and corrections applied 

 in the reductions. 



Unfortunately a small portion of the manuscripts was lost by the 

 fire which destroyed a part of the Smithsonian building in January, 

 18G5. This loss was partly supplied by the monthly means which 

 had been published by Dr. Hildreth in Silliman's Journal. 



During the 40 Marietta years a mean temperature is shown of 52°.46. 

 The mean temperature of 1828, the warmest year during the whole 

 period, was 55°. 38, and that of the coldest, 1856, was49°. 71, show- 

 ing a range or variation of temperature of 5°. 67, which is about 

 the usual range of annual temperature, as indicated by shorter periods 

 in our latitude. The discussion indicates no change of annual tem- 

 perature during the whole period of 40 years, the mean temperature 

 of the first 20 years being the same as of the last 20 years. Neither 

 do these observations indicate any change in the temperature of 

 summer or winter by comparing the first 20 with the second 20 

 years. We tliink it probable, however, that a full discussion of all 

 the records collected by the Institution would show some slight change 

 in the average temperatur-e of summer and winter due to the exposure 

 of the surface by the clearing away of trees, although no indications 

 of a similar kind may be given in the mean temperature of the year. 



The greatest fluctuation of temperature is in February, and the 

 least in July and August. The lowest temperature during the whole 

 period was 23 degrees below zero, Fahrenheit, at 7 o'clock a. m., 

 January 20, 1852; the extreme highest 102 degrees at 3 p. m., July 

 14,1859. These observations give an extreme range of temperature 

 of 125 degrees, which, when compared with that of Euiope, may be 

 considered excessive, but, compared with that of other parts of 

 America and Asia, is not unusual. From all the observations it appears 

 that, on an average, the warmest day of the year is the 23d of July, 

 and the coldest the 15th of January, while the days which have the 



