EFFECTS OF LOCALITY ON TEMPERATURE. 



21 



difference of elevation of about 80 feet, and tlie 

 peach trees on the lower part did not produce 

 hardly a single blossom, while trees on the 

 highest ground had a good supply of bloom. 

 The small branches of many on the low ground 

 are killed, and even some of the apple trees 

 there are injured, as if by the extreme cold 

 weather. The heart cherries, though on high- 

 er ground, have suffered ; some of their blos- 

 som buds remain undeveloped, and even where 

 the bloom was considerable, there are very 

 cherries to be seen. The morello cherries do 

 not seem to be injured, and the apple trees 

 had a heavy bloom. They are all much later 

 than usual ; the peach did not come into full 

 bloom before the 25th of last month, about 

 three weeks behind the usual time. On all 

 high situations in this vicinity, the peaches 

 promise a full crop, while in all low ones, no 

 blossoms were seen. 



After examining the effects, the theory 

 seems to be this : When the ground is covered 

 with snow, so as to prevent any radiation of 

 heat from the surface, and the air is perfectly 

 still, the caloric in the air [i. e., the warmer 

 strata of air,] will rise higher and leave the 

 the cold air in the valleys below. This being 

 continued for several days, must produce a 

 great degree of cold there. But had tliere 

 have been any wind, this separation of the air 

 into colder and warmer strata, would not have 

 taken place near the surface of the earth, for 

 it would all have been mixed up, and have re- 

 sulted in a uniformity of temperature in all 

 places alike. 



In the winter of '34-'5, we had a snow 

 here near eighteen inches deep ; the ground 

 was not frozen when it fell, and it continued 

 calm weather, without any wind, for near a 

 week, when one morning the thermometer in 

 low situations fell to 20° below zero, a de- 

 gree of cold never witnessed here by ma- 

 ny of us before. The peach trees suffered 

 (Severely ; many of them were almost killed ; 



nearly all the smaller branches were destroy- 

 ed, and in low situations they only put out 

 shoots, when they did, far back on the larger 

 branches. In this case a surprising difference 

 of temperature was exhibited on different le- 

 vels. While the thermometer in the valley 

 near the west side of Catoctin mountain in- 

 dicated 20° below zero, one at Mt. Gilead, 

 on the mountain perhaps 200 feet above, and 

 only a few miles distant, was only down to 

 zero. And the different effects upon the peach 

 trees in this instance, in the two extremes of 

 level, would seem to confirm such a difference 

 of temperature, for on the mountains they 

 were but little injured. 



Another remarkable instance of the same 

 principle, occurred here in the spring of '34. 

 Between the 13th and 17th of the 5th month 

 (May) of that year, we had a succession of 

 frosts that froze the ground of nights, and 

 fqjrmed ice of the thickness of window glass. 

 The forest trees were out in leaf, many of 

 them nearly full grown, and with young shoots 

 six or eight inches long, and the peaches were 

 as large as ripe currants. A destruction of 

 fruit was the consequence for that season, and 

 the effect on the forests in some instances was 

 remarkable. I noticed a few days afterwards, 

 in a small valley or ravine near Alexandria, 

 that in the bottom of the valley, and up the 

 sides of the hills to a certain level, the young 

 leaves and shoots were entirely killed, and 

 looked as if scorched by the fire, while above 

 that level they were still alive. This level, 

 in looking up the valley, as there was consid- 

 erable size to it, reached the bottom of it, and 

 was visible no further, while down the valley 

 it passed along the sides of the hills some dis- 

 tance from their base, and exhibited the fact 

 of many trees that stood below the level of 

 this line, having the leaves and shoots entire- 

 ly killed on the lower limbs, while those on 

 the higher branches were still alive. 



It would seem from the above facts, that a 



