870 Proceedings of the British Association. 



The line of mean pressure occurred between the hours of 1 and 

 2, and between 7 and 8, A, M. ; and again between 12 and 1, and 

 between 6 and 7, P. M. The hourly vnaximum 'pressure was at 

 10 o'clock, morning and night ; being, with only one exception, 

 the uniform result for six years. The hourly minimum pressure 

 occurred at 4, A. M. and P. M., being the uniform result for six 

 years, without any exception. The line of mean pressure was 

 crossed four times in the 24 hours ; and thus was realized, in the 

 midst of atmospheric disturbances of very considerable amount, 

 that effect, termed horary oscillation, which was first observed 

 by Baron Humboldt, in tropical climates. Mr. Airy, to whom 

 these observations were submitted, seemed to think, that but lit- 

 tle now could be effected by continuing them after the close of 

 this year. There had been 48,000 hourly observations on the 

 atmospheric pressure, and 87,000 hourly observations on the tem- 

 perature : and he trusted these would not be preserved merely in 

 the perishable form of manuscript, but placed at the disposal of the 

 scientific world. After explaining the construction of Whewell's 

 anemometer, he said, that when the pencil tracing the integral 

 effect of the wind, moved at the rate of one tenth of an inch per 

 hour, the current of air at the same time moved at a mean rate of 

 eleven feet per second. He (Mr. H.) had, by means of this in- 

 strument, endeavored to arrive at something like an approxima- 

 tion to the velocity and direction of what he believed would 

 amount to a trade-wind. He had a table of results which gave 

 the mean velocity of the wind, in feet per second, for each month 

 of the year, viz. 



So that the mean velocity of the wind during one year, (leav- 

 ing the direction out of the account,) was about nine miles per 

 hour. If the mean velocities arrived at in this table were dimin- 

 ished and made proportionate to the whole length of the wind, 

 we should then have something like a general idea of the velocity 

 of the aerial current, as deduced from observation and inquiry. 



