212 



METEOROLOGY, 

 No. 5 — Continued. 



From this we see that during the time from April 3 to Atiril 22— 



The E and ESE. rurrenis liave been chit fly in no olliir but the lov;cr ftrata. 



The SE., S , and ri W currents have been cliiefly in no other but the lower and midrile strata. 



The VV , W SW , and N. W. currents have been' chiefly in no other but the vjijicr and middle strata. 



The N. cu rent has been in all three sirata, the upper, miildlc, and lower strata. 

 Or expre-sed in another manner — 



In the vjipcr region occur chiefly W ,NW , W SW., N. 



In the wiMIe region occur • hi. fly S., SE , W., SW., N., NW., N.NE. 



In the lower region occur chiefly S., SK , E., E.SE. 



CoLONiA TovAR, VENEZUELA, June 11, 1857. 



Dear Sir : Your kind letter of March 5, was received by me in due 

 time, and a little box with eight pounds of mercury, for which I 

 thank you very much, came to hand somewhat later, on the 3d of May. 



Soon after the receipt of the mercury I went to work to fill the 

 barometer tube accoiding to your directions ; but with every new trial 

 I ibund that the mercury fell more and moie below its standard 

 height, although I was certain there could be no air above it. At 

 first I could assign no cause for this failure ; but the fact that I was 

 losing regularly at every new trial suggested to me the idea, that in 

 handling the mercury the latter might have taken moisture from the 

 atmosphere. Accordingly, I placed the barometer tube containing the 

 mercuiy and a Torricellian vacuum in a nearly horizontal position 

 cautiously over a brisk charcoal fire, and in this way htatfd the 

 mercury for some time, until no more bubbles were disengaged. I 

 was hereby especially struck with the great quantity of escaping 

 moisture, and never thought that mercury could have taken up so 

 much from the atmosphere during the short period required lor filling 

 the tube. Can this property be due to the nitric acid, with which the 

 mercury may have been purified, and which is known to absorb mois- 

 ture from the air? Thus, by boiling, and at the same time making, 

 use of your directions, I succeeded perfectly well in bringing the level 

 of the mercury up to its standard value. In such a damp atmosphere 

 as this the boding of the mercury seems to be indispensable. 



I have now the pleasur( to say, that since the 9th of May the 

 barometer may be considered to be as correct and precise as when I 

 first received it. 



In a separate envelope accompanying my present communication, I 

 have the pleasure of sending you besides the meteorological registers 

 for six months, a short essay on the cause of the daily periodical 

 variations of the baroujeter, and a number of tables and diagrams. 



