METEOROLOGY. 217 



5, 3, 4, 5, 3, 7, 3, 5, 4, 5, 3, 6, 6, 4, 4, 2, 4, 6, 5, 5, 3, 7, 4, 6, 4 = 

 167, of which the mean is 4.5 days, as the mean period occurring be- 

 tween every two succes-sive heights or vertices. 



The same process applied to the former diagram of the months of 

 June to October, 1856, gives me the following numbers: 5, 4, 5, 3, 

 5, 3, 4, 4, 4, 5, 6, 5, 4, 6, 3, 4, 3, 4, 3, 6, 4, 3, 4, 6, 10, {= 2 + 5,) 

 5, 5, 5 =: 128, of which the mean number is 4.4 days. For May, 

 1857, commencing with the 14th, the numbers are 3, 5, 5, 5, 3. 



No m-itter whether the barometer had a perfect vacuum or nof , the 

 features of this remarkable phenom^enon are the same. The two series 

 of the above numbers, and the coincidence of their mean value, prove 

 beyond a doubt that they are not the result of mere accident ; but that 

 this i)eriodical fluctuation in the pressure of the atmosphere is subject 

 to a certain law, of whicli I am ignorant. 



l>iaiiram No. 9 exhibits two curves of the mean temperature for 

 Colonia Tovar for twelve months. The upper curve is the result of 

 noting down the mean temperature for evexy third port of the month, 

 and presents quite a different appearance compared with the lower 

 curve, in which are noted down the mean temperatures of the whole 

 months only. The latter part of April and the middle of September 

 show the highest, and the middle of January the lowest teniperature. 

 July has usually a lower temperature than the three months on either 

 side of it. The mean temj)eratures of the four meteorological seasons 

 present the curious fact that three of them, spring, summer, and 

 autumn, have exactly the same temperature, viz : 58.9, even to a 

 fraction. The mean tem}»erature of the year is 58.2 ; difference be- 

 tween the coldest and warmest month, 5.3. 



The temperature of the primeval forest, about two hundred yards 

 distant from my dwelling, was, on the 25th of April, at \h. iSOm. 

 p. m., 61°, at the margin 64°, when at ray house the thermometer 

 was 65°. In a shady ravine I stuck the thermometer four inches deep 

 into the spongy brown vegetable mould at different times of the day, 

 and found the temperature always 59°, pretty near the mean tem- 

 perature of the year. 58° or 59° may be considered to be the constant 

 temi)erature of this region about twelve inches below the surface of 

 the y;round in shady places. 



I have often observed that, whenever the sun breaks through the 

 clouds and has been shining for a couple of hours, the thermom- 

 eter fluctuates frequently very suddenly from one to four degrees, 

 according as it is touched by a warmer or colder current of air pro- 

 ceeding from the diifrently heated localities of the soil; but when 

 the sky is entirely overcast such changes never take place. 



It seems somewhat remakable that, at Colonia Tovar, no heavy 

 thunder-storms occur. Thunder and lightning are seldom strong 

 enough to deserve to be mentioned. Trusting to past experience 

 with regard to the absence ol tempests, hurricanes, and whirlwinds, 

 I have covered the roof of my house with very thin and light shingles, 

 not nailed down, as is done in the States, but merely hung loosely 

 upon laths without any weather-boarding at all. And yet, for two 



