Mr. W. R. Birt o« Atmospheric Waves. 483 



hausen Wynberg, near the Cape of Good Hope. These were 

 accompanied by a simultaneous set at the Royal Observatory 

 near Cape Town. The observations thus set on foot were 

 continued at numerous stations during the followino' three 

 years ; and the discussion of the whole, collected by Sn- John, 

 forms the subject of a report presented by that gendeman to 

 the British Association during its sitting at Cork in the year 

 184.3. One of the objects to which Sir John directed his 

 attention in this discussion, was the barometric fluctuations 

 considered with a view to the propagation of atmospheric 

 waves. For this purpose the stations were distributed in 

 groups, in one of which (the European) Sir John succeeded 

 in detecting and tracing two well-defined waves ; one on the 

 21st of September 1836, the other on the 21st of December 

 1837. These waves were so vast in their dimensions, that to 

 take in (says Sir John) an effect of this nature, we must enlarge 

 our conception of an atmospheric wave till it approaches in 

 some degree, in the extent of its sweep and the majestic regu- 

 larity of its progress, to those of the tide-waves of the ocean*. 

 The principle on which the discussion of these hourly ob- 

 servations was conducted, was that of projecting the baro- 

 metric curves for all the stations of one group on a1;ingle sheet 

 for each separate term, the scale being one inch to an hour in 

 tijyie, and one inch to O'n-066 of barometric altitude. From 

 the nature, however, of the observations, no one curve was 

 continued longer than twenty-four hours, except on the occa- 

 sion of a remarkable storm. During the progress of this 

 work, it was deemed desirable to obtain the complete rise and 

 fall of the barometer ; so that a complete wave might be ob- 

 served at least at one station. Observations undertaken with 

 this view, and projected in curves, illustrate Sir John Her- 

 schel's report. As a test of any conclusions that may be drawn 

 from a discussion of observations on this principle, the obser- 

 vations may be so combined as to exhibit, not only the baro- 

 metric relations with regard to time, but also with regard to 

 space : in other words, the distribution of pressure over a 

 tract of country, at any given epoch, will indicate the real 

 character of the waves then transiting. 



The last report which I had the honour to present to the 

 British Association during its sitting at Southampton, contains 

 an examination of certain l)aronietric observations exclusively 

 on tlie last-named principle. These observations were made 

 during November 1842, the same month in which the obser- 

 vations were made from which some of the curves illustratin'"- 



• Report of the Tliirtcciilli Meeting of the British Association for the 

 Advancement of Science, m. G0-10.*J. 



2 K 2 



