358 Combination of Meteorological [June, 



hitherto unexplored region of the southern hemisphere. It is what we have 

 been attempting to do for India, and not without success, although we have 

 hitherto avoided publishing the many registers with which we have been favored, 

 until they could be put together in a convenient form for comparison and analysis. 

 There will be a double advantage in having a counter-series south of the line, for 

 Sir John had already announced to us the discovery, on comparison of the tables 

 given in our Journal, with a series of 57 months kept by the Post Master at the 

 Cape, that the annual fluctuation in the Barometric tide there, having regard to 

 the difference of latitude, is precisely complementary to ours : that it amounts to 

 0.29 inch, on an average of the whole period ; the maximum taking place about the 

 21st July, and the minimum about the 19th January : " thus in the latter month 

 when the Barometer in Calcutta stands 0.25 inch higher than the mean, and that 

 at the Cape, 0.15 lower — a propellant force equal to the weight of a column of 

 mercury, 0.4 inch, urges steadily and constantly the air towards the south, and vice 

 versa ; nor can its influence be confined to small tracts, but from its very magni- 

 tude and nature, it must communicate motion to immense masses of air." 

 When a master hand approaches the ordinary, yet complicated subject of winds 

 and weather, general results of great practical utility and importance are sure of 

 development. Their appearance in the field should not however discourage other 

 labourers, but rather stimulate their investigations: each separate branch of 

 inquiry is in this science so laborious, as more than to occupy one head. The 

 influence of the sun, of the moon, of oceanic coasts, of mountain ranges, are all 

 separate questions of great intricacy. 



The principal difficulty is to provide, that observers shall all note down on the 

 same days and hours : we observe sun-rise, noon, sun-set, and midnight, recommended 

 at the Cape, also 8 a. m., 2 p. m., and 8 p. m. Now the knowledge of the hours of 

 maximum and minimum has made us prefer 10 a. m. and 4 p. m., 10 p. m. and 

 4 a. m. ; but in our own and the Surveyor General's series, we have enough points 

 to fill up the whole daily curve of temperature and pressure for Calcutta. With 

 regard to this essential point, we have been requested to call the attention of our 

 meteorologists in India, Ceylon, the Straits, and China, to the following determina- 

 tion of the Cape Committee, to devote four days of the year to horary observations. 



"With a view, however, to the better determining the laws of the diurnal 

 changes taking place in the atmosphere, and to the obtaining a knowledge of the 

 correspondence of its movements and affections over great regions of the earth's 

 surface, or even over the whole globe, the Committee have resolved to recommend, 

 that four days in each year should henceforward be especially set apart by 

 meteorologists in every part of the world, and devoted to a most scrupulous and 

 accurate registry of the state of the Barometer and Thermometer ; the direction 

 and force of the wind ; the quantity, character, and distribution of clouds ; 

 and every other particular of weather, throughout the whole twenty-four hours 

 of those days, and the adjoining six hours of the days preceding and following*. 



* This is necessary by reason of the want of coincidence of the day in different 

 parts of the globe, arising from difference of longitude. In order to obtain a 

 complete correspondence of observation for 24 successive hours over the whole 

 globe, it must be taken into account that opposite longitudes differ 12 hours in 

 their reckoning of time. By the arrangement in the text, the whole of the astrono- 

 mical day (from noon to noon) is embraced in each series, and no observer is required 

 to watch two nights in succession. 



