METEOEOLOGY. 223 



hour between 2 and 3 p. m., and tlien sinks to 10 p. m. nearly as 

 gradually as it rose. 



No. 4. A table giving the course of the clouds of the higher, mid- 

 dle, and lower strata for the months of June to December, 1857. 

 The motion of the clouds from the E., E.SE., 8E., S.SE., and S. is 

 by far the most prevailing, amounting to 415, while the motions from 

 all the other eleven points amount only to 133. November and De- 

 cember show, as usually, a preponderance over the eight preceding 

 mouths with regard to motion of the clouds from the northern re- 

 gions. The motions from the west, with only one exception, took 

 place in the highest regions of the atmosphere. This puts me in 

 mind of the fact that, while at Santa Fe, New Mexico, the steady 

 course of the higher clouds from the west had frequently attracted 

 my attention. 



No. 5 gives a view of the fluctuation of the mean daily heights of 

 the barometer for seven months. My remarks in a former letter about 

 the falling and rising of the mean daily height of the barometer, 

 which from one maximum to another requires, on an average, 4| days, 

 still hold good, as will be seen by the following series of numbers, 

 which are the number of days counted from one maximum height to 

 the next following one. 



Beginning with my earliest barometrical observations, counting 

 from the 14th of June, 1856, and ending with the 30th of October, 

 1856, the day on which the barometer got out of order, we have: 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, 5, 



5, 5 = 128 days, of which the mean is 4.57 days. 



JL3eginning again, when the barometer was put into use, with the 

 12th of November, 1856, and ending with the 30th of April, 1857, 

 the day on which the barometer was taken apart to be mended, we 

 get : 6, 5, 2, 5, 6, 4, 4, 3, 6, 4, 6, 3, 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, 2 = 169 days, of which the mean 

 is 4.45 days. 



Beginning again, when the barometer was in good order, with the 

 13th of Mav, 1857, and ending with the 31st of December, 1857, we 

 get: 2, 3, 5, 5, 5, 3, 4, 5, 4, 4, 3, 3, 3, 2, 4, 8, 4, 4, 5, 3, 4, 7, 2, 5, 

 4, 4, 5, 6, 5, 4, 5, 2, 4, 4, 2, 5, 3, 7, 7, 5, 4, 4, 5, 6, 4, 5, 10, 8, 6, 

 6, 3 ^ 230 days, of which the mean is 4.51 days. 



The mean of all these three series is 4.51 days. 



No. 6 contains the half-hourly observations on the daily periodical 

 variations of the barometer for 157 days, which, together with those 

 made from the 10th of May to the 10th of Juno, amount to 186 days, 

 including more than 2,000 half-hourly observations of the barometer. 

 Duiing these seven months* I was, if I may use the expression, " liv- 

 ing under the clock ;" for I had to keep a continual lookout for the 

 arrival of the moment when one half hour after another would be up. 



How often was I interrupted in my out-door manual labors in order 

 to attend to these observations ! And but the desire to help carry a 

 few useful materials towards the building ground of the great struc- 

 ture of meteorology, which no doubt one day will be reared in all its 

 perfection, could keep me at work with patience unwearied. I should 

 have continued these half-hourly observations still longer, but my 



