Mr. W. R. Birt on Atmospheric Waves. 501 



Upon comparing the numbers at the Orkneys with those at Paris, 

 as given in Table I., we at once recognise a considerable difference 

 in the oscillation at the two stations. At the Orkneys it amounted to 

 1*72, at Paris to '79, range at the Orkneys in excess ■93. It appears 

 probable that this difference of oscillation at two stations, as the Ork- 

 neys and Paris, may be thus explained. The curves in the north- 

 west of Ireland, as determined by the discussion of Sir John Her- 

 schel's hourly-observations, are remarkable for boldness and freedom 

 of contour and great range of fluctuation. The late Professor Da- 

 niell found, from an examination of the Manheim observations, that 

 the range increased towards the north-west, and that the greatest 

 oscillation occurred in the neighbourhood of water. Now a wave 

 generated in any way and approaching the continent of Europe from 

 the north-west, would most probably impinge on it with a high and 



in some cases acuminated crest y \ , but as it passed 



onward the crest would gradually subside ^-^ ^-^^^ ^ > 



so that at stations considerably to the south-east the fluctuations 

 would be very much less than at or near its point of genesis. Again, 

 a negative wave, with a deep trough also approaching from the north- 

 west x,^ /^ , would present large fluctuations as it im- 

 pinged on the land ; but after passing onwards, the opposite to sub- 

 sidence would take place ; the deptli of trough would decrease, 

 ~^ , and the oscillations to the south-east would 

 also decrease. Such phtenomena appear to be presented by the ob- 

 servations from the 5th to the 10th of November 184-2. 



In connexion with this subsidence of crest No. 2, as it passed from 

 N.W. to S.E., it may be interesting to notice the passage of crest 

 No. 3, the circumstances of the transits of the two waves being dif- 

 ferent; wave No. 2 com'mg froin the sea, and passing over Ireland, 

 Scotland and England, and the land forming the central part of 

 Europe ; while wave No. 3 skirted the western and north-western 

 boundaries of Europe, and more or less passed over the waters of 

 tlie Atlantic and Nortii Sea. The crest No. 3 came from the S.W., 

 so that a line from Plymouth to Christiania would cut it more or less 

 transversely ; the ranges liowevt.T are ncuirly the same at both stations. 

 Tiie crest which traversed England on tlie 1st arrived at Christiania 

 on the 4th ; at this time the barometer had conunenced rising at 

 Plymoutii from tlie anterior slope of crest No. 2, and it continued 

 rising until the 7tli, when the crest passed. At Christiania the ba- 

 rometer had fallen from the posterior slope of crest No. 2. It ap- 

 pears from a careful comparison and consideration of the barometric 

 movements at Plymouth and Ciiristiania, that crest No. 2 jiassed 

 Christiania about a day earlier than it did Plymouth, that is, the lon- 

 gitudinal direction of the crest was such as to cause it to pass over 

 Christiania while Plymouth was still under the anterior slope of the 

 wave, the sections ])assing over C'hristiania and Plymouth being 

 separate and distinct. The cliaractor of the passing wave is well- 



