216 



FARMERS' REGISTER— CLIMATE OF VIRGINIA. 



examination oi" the temperature of .the otli^r parts 

 of the Btate, to rely on statements often inaccurate 

 in tlieir Conception and iri'elevant in their details. 



The standard temperature of every country is 

 regulated by tlaat of the level of the ocean. Ac- 

 cording to the researches of Professor Leslie, the 

 mean tempemture at the level of the sea, in our 

 latitude is bet-ween O?"^ and 71° degrees, which 

 gradually diminishes from that level, until it reach- 

 es the point of perpetual congelation. Pure air is 

 not heated by the sun's rays which pass througJi 

 it; the solar rayc must be stop})ed by the earth, 

 colbcted and reflected before any heat can be. given 

 to the atmosphere. In taking a standard, we as- 

 sume the sea, which affords a fairei' criterion of 

 uniform temperature, than the mean heat of springs 

 and wells. Neither does the sea retain the ex- 

 treme of heat or cold \vhich we find in the earth. 

 A cold wind blowing over this volume of salt wa- 

 ter, necessarily cools its surface, which from its 

 increase of specific gravity, sinks and ^ives place 

 to an inferior warmer wave. The action of the 

 wind in rippling the surface of the water, and the 

 influence of tide and currents conspire in bringing 

 the warmer water to the level oi" the sea to miti- 

 gate the coldness of the wind: this action contin- 

 ues till the whole water is so tar cooled that it be- ' 

 comes susceptible of frost. When li-ozen it is no 

 longt^r w^armed from the inlerior water, but blows 

 on \vith increased rigor. A warm v/ind takes a 1 

 portion of cold as it passes over the'surface of the j 

 K^ea, and becomes reduced to the mean tempera- 

 ture of that body. The sea breeze so prevalent 

 in Eastern Virginia is coo! as nmch tl-om the stand- 

 ard heat of the ocean, as fi'om its rapidity of mo- 

 tion: it is cooler in Virginia than in the West 

 Indies, and often since the opening of the country, 

 spreads its elastic freshness to the foot of the South 

 West Mountains. There is a sensible and striking 

 difference between the temperature of Eastern 

 and Western Virginia. The former from its vi- 

 cinity to the sea coast, becomes tempered into more 

 gentleness; while its earlier vegetation shows the 

 greater power of its soil to retain heat. In the 

 latter, the winters are longer and more severe, yet 

 the farmer njay there admire the wisdom of that 

 providence, which in increasing the rigor of the 

 frost, mellows and crumbles tire land for the pur- 

 poses of agriculture:, while the light soils of the 

 east require no such agency. 



In the course of five years, from 1772 to 1777, 

 Mr, Jefferson made many observations on the 

 temperature at Williamsburg, and having reduced 

 them to an average for each month in the year, 

 lie has given us the results of the greatest daily 

 heat of the several seasons.* I liave before me a 

 serifes of careful observations compiled by that 

 accyrate thinker, and accomplished scholar, the 

 late David Watson, (of Louisa County) in a simi- 

 lar pmod of five years, from 1823 to' 1828. His 

 residence was near the South West Mountains,and 

 in a country comparatively thickly covered with 

 AvooJ. The result of his observations and those 

 of Mr. Jeffersons, making a distance in time of 

 62 years, and of southern latitude in favor of Wil- 

 liamsburg, is here submitted. 



* JVotes on Virginia, Query 8, 



The coolest and warmest parts of the day were 

 separately added, and an average of the greatest 

 cold and heat of that day was formed. Frorp the 

 averages of every day in the liionth, a general 

 average for the whole month was deduced. In 

 ibllowing this mode of analysis, there are many 

 slight features of discrepancy between the state- 

 ments of Mr. Jefierson and Mr. Watson, which 

 considerably impair the correctness of the com- 

 parison. Mr. Watson's thermometer was sus- 

 jiended in a passage, fiir removed from the action 

 of fire, in a house constructed of wood; and the 

 calculation of his table is based on observations 

 made between the hours of 10 A. M. and 3 P. M. 

 Mr. Jefferson is silent as to the situation oi^ his 

 thermometer, while it appears that he has reck- 

 oned from the hours of 8 A, M. to 4 P. M. 



The hottest period of these five years, observed 

 by Mr. Watson, was in July 1825, when the 

 thermometer on several days rose above 90°, and 

 the hottest month was in August 1828. The 

 coldest period was during the month of January 

 1827, and the warmest winter was in 1828—29. 



My own observations made during a period of 

 four years, from 1829 to 1834, cannot be calculated 

 lor an average temperature. Many days and 

 even months fi"om my absence from home, were 

 necessarily unnoticed. Those periods which are 

 recorded differ but little in their particular and 

 daily residts, fi-om those of JNIr. V/atson; while I 

 have noticed his singular omission — the preva- 

 lence of the Avinds, and the " fi\ntastic tricks" with 

 which our climate so playfully disports. From 

 my observations, 1 am induced to place the mean 

 temperature of our climate at 55°; thus varj'ing 

 according to natural and artificial causes several 

 degrees from the standard temjierature of the sea. 



The year 1831 was characterised by many vicis- 

 situdes of heat and cold. On the 2'i'th FebruaVy 

 the mercury sunk to 7°, while in July and August 

 it frequently rose to 86° and 94°. "The ensuing 

 winters of "1831 and 1S32 Avas uncommonly ri- 

 gorous, snow fell in great quantities, and in mapy 



