482 Mr. W. R. Birt on Atmospheric Waves. 



subject. At presentj when the ground is so wet, it is difficult 

 to obtain u sufficient quantity of the saUs, which are pecuhar. 

 At present I may say that sulphuric acid added to the water 

 gives off chlorine ; that heat evolves chlorine and peroxide of 

 nitrogen from it; and that the I'emaining salt is a mixture 

 of a chloride and a nitrate chiefly. This will be sufficient to 

 show that neither the water nor the air of Manchester has so 

 very minute an amount of impurity as to put it without the 

 power of detection. 



LXXVI. On certain Atmospheric or Barometric Waves which 

 traversed Europe during November 1842. By William 

 Radcliff Birt*. 



A T the sittings of the Geological Society on the 3rd and 

 -^^ 17lh of May in the year 1816, a paper was read by Dr. 

 MaccuUoch On the Employment of the Barometer in mea- 

 suring heights. In this paper the author endeavoured to show 

 that the differences indicated by different instruments, placed 

 at various stations on the earth's surface, are real differences 

 of atmospheric pressure, and that the changes which take 

 place at several stations are far from being simultaneous : he 

 also expressed an opinion, that the differences of pressure, 

 combined with their progressive character, are in some way 

 or another connected with the direction of the wind, especially 

 the two cardinal currents N.E. and S.W. of our island ; but 

 the imperfect state of the barometer at that time was such as 

 to prevent an efficient investigation of the subject. 



in the year 1832, Professor Forbes, in his Report on the 

 Recent Progress and Present State of Meteorology, presented 

 to the British Association for the Advancement of Science 

 during its sitting at Oxford, alluded to the accidental variations 

 of barometric pressure as gi'eatly influenced by latitude, the 

 amount of variability increasing towards the poles. Reap- 

 peared to regard these variations as resulting from great 

 atmospheric tidal xaaves, which perpetually traverse our oceans 

 and continents, and he viewed a future and more advanced 

 state of meteorological science, as furnishing data from which 

 the most interesting and important conclusions might be drawn 

 in immediate connexion with such atmospheric waves f. 



On the 21st of March in the year 1835, Sir John Herschel 

 made a series of hourly meteorological observations at Feld- 



* From Report of the British Association for the Advancement of 

 Science for 1846. 



t Report of tiie First and Second Meetings of the British Association for 

 the Advancement of Science, p. 235. 



