1867.] 



Atmospheric Tide at Melbourne, 



495 



be judged by the mean values for the respective two months, representmg, 

 as they do, in both cases a distinct oscillation with an amplitude of 0"'01722 

 for the solstices, and of 0"'01041 for the equinoxes. I may be allowed to 

 refrain from adding here these mean values, suffice it to refer to the 

 respective curves at the bottom of Plate II. For December and June we 

 observe the maximum to occur at 23'', the minimum at or shortly after S'^, 

 while for September and March the maximum in the lunar-diurnal varia- 

 tion of pressure of air takes place at 7^' and the minimum at 19'\ The 

 mean for the quarters (each embracing six months) show the same charac- 

 teristics, though by far less in extent, the amplitude for the solstitial 

 quarters being 0"*007454, and that for the equinoctial quarters 0"'006334, 

 There is another fact which requires to be pointed out, in order to throw 

 further light upon the character of these oscillations ; namely, that they 

 seem to bear a great resemblance for both hemispheres during the same 

 semiannual period, if we are permitted to arrive at this conclusion by re- 

 ferring to Prof. Ereil's discussions of his observations at Prague (Versuch 

 den Einfluss des Mondes auf den atmospherischen Zustand unserer Erde 

 aus einjahrlgen Beobachtungen zu erkennen, 1841). The semiannual 

 curves of the lunar-diurnal variation of the barometer at Prague and Mel- 

 bourne closely correspond during the months from April to September, and 

 from October to March, which seems to point to some cause common to 

 the whole globe in a similar manner, as we know it to be with respect to 

 the extent of the rise of the oceanic tides at the time of the solstices and 

 equinoxes. It would be premature to enter now upon any speculation 

 with a view to bring the results of our observations in accordance with 

 theory, there being still by far too few discussions on atmospheric tidal 

 observations at our command. 



The yearly curve of the lunar-diurnal variation presents some peculiarly 

 interesting features, differing in some respects from the results of similar 

 inquiries instituted by General Sabine and Capt. C. M. Elliot with special 

 regard to the lunar atmospheric tides at St. Helena and Singapore, al- 

 though the plan of discussion was the same. The lunar horary variation 

 of the barometer is as follows, ''if we arrange the results in such manner 

 that the hours are combined in which the moon is similarly situated in 

 respect to the meridian" (Sabine's paper "On the Lunar Tides at St. 

 Helena") :— 



