216 METEOROLOGY. 



Among the number of days free from clouds we find that at 2 p. m. 

 throug^hout all the twelve months there was only one sintrle day where 

 the sky was entirely clear, but at 9 p. m. we liad a clear sky on eighty- 

 eight days. In the month of September the sky was during all the 

 ninety observatinns made in that month more or less clouded. At 2 

 p. m. the sky was entirely overcast on one hundred and thirty-five 

 days. In May it was entirely overcast during forty-seven observations. 

 The number of rainy days is two hundred and thirteen. 



Table No. 5 contains observations on the motion of strata of clouds 

 of different heights. 



Observations on the motion of the highest clouds would be very 

 important, but in this region we are unable to make a great number 

 of such observations on account of the cloudy state of the sky, and we 

 have to make the best of the few opportunities we may now and then 

 get. As April is one of the most favorable months for this purpose, 

 1 have chosen this time, and have taken peculiar pains in collecting 

 the facts contained in table No 5. The greatest difficulty hereby ex- 

 ists in telling exactly which of the many different thin strata of clouds 

 are the higher and which the lower ones. I was sometimes obliged 

 to watch them for ten minutes right over head ; but knowing that 

 inaccurate observations are infinitely worse than none at all, I did not 

 shun any inconvenience to arrive at the true motion of the different 

 strata. 



From this table we see that in the upper and highest regions the 

 following winds were observed chiefly to occur: W.NW., W.SW., 

 N. ; in the middle regi' ns, sav from 7,000 to 9,000 feet above the sea, 

 S SE., W.SW., N.NW., N.NE ; and in the lower region, say from 

 7,000 down to 5,000 feet and still lower, S.SE., E., ESE. 



I may here remark that, from long continued observation on the 

 motion of the clouds, 1 am inclined to believe that all the easterly 

 winds of this region are gradually ascending in their course towards 

 the west, while the southern as well as the western currents are 

 gradually descending in their course. 



Diagram No. 7 gives a view of the curve of mean monthly tempera- 

 ture for Colonia Tovar compared with the curves for New Orleans, St. 

 Louis, Missouri, and Boothia Felix. I have chosen these three latter 

 places because they are all North American, and lying nearly under 

 one and the same degree of longitude, but in difierent latitudes ; 

 Boothia Felix in north latitude 70.2°. 



Diagram No. 8 contains all the mean daily heights of the barometer 

 from November 7, 1856, to April 30, 1857, and from May 9 to June 3. 

 A similar diagram for June to October. 1856, I have sent alrea ly with 

 one of my former letters. At that time I remarked that a kind of 

 periodical rising and falling in periods from four to five days was ob- 

 servable, but I did not then expect that this rule would hold out for 

 the remainder of the year. ' But after I had finished diagram No. 8, 

 merely to see what kind of curve these months would present to the 

 eye, I was struck with its appearance in siiape, and induced to count 

 the days from vertex to vertex, which, commencing with November 

 11, gave me the following numbers : 6, 5, 2, 5, 6, 4, 4^ 3, 6, 4, 6, 3 



