74 Proceedings of the Royal Irish Academy. 



liour; when the moon's declination is south, this will be the smaller 

 tide." This is precisely what theory advances (see ""Wlieweirs 

 Dynamics," part i., ed. 1832, p. 198); and I am not aware that the 

 true theory, as it is called, which is based on the Harmonic Analysis 

 of the Tides contradicts the more anciently-received one. But, in 

 point of fact, and as the result of observation, the configuration of 

 land and water is such as to cause that tidal wave, whose pole is, or 

 ought to be, in the northern hemisphere, to be invariably of lower 

 magnitude than that whose pole is in the southern hemisphere; and, 

 as I take it, the simple reason of the contrariety is, that neither moon 

 nor sun can possibly generate a tide in regions where little or no 

 water exists for the purpose. 



What observation shows is this — that the lunar tide is greater 

 than the anti-lunar which follows it, whenever the moon's declina- 

 tion ranges from 20 deg. S., ascending to about 15 deg. N. ascending ; 

 and the anti-lunar tide is greater than the lunar whenever the 

 moon's declination ranges from 20 deg. IST., descending io about 15 deg. 

 S., descending ; the parallax being the same throughout. 



A few words must be added in explanation of the accompanying dia- 

 gram. The figures at the side denote the successive feet as marked on 

 an Admiralty Tide-gauge, whose base is the mean level of low water 

 of ordinary spring tides. The figures at the top of the page point out 

 the days of the month during which the observations were made, and 

 the letters " w," " e," refer to the morning or evening tide, as the 

 case may be. The figures in the middle of the diagram refer also to 

 the days of the same month, but each of them is put a day and a-half 

 antecedent to those in the top line, because there is that interval from 

 the ''transit B " of Sir John Lubbock, during which the tide travels 

 from its cradle in the South Pacific to the Irish Sea. The tides are 

 marked alternately by dotted and by straight lines, the latter indi- 

 cating what we have called lunar, and the former anti-lunar tides, 

 and they are laid down to scale, thus showing by the lines joining 

 the summits the course of the curve they form. "Within the space at 

 the lower part of the diagram, the moon's path and that of the sun 

 are plotted also to scale, and the dotted lines show those of the 

 " anti-moon" and« " anti-sun." A glance from the top to the bottom 

 of the diagram, in the direction of the lines which mark each tide, 

 enables us to complete our description. If we take the morning tide 

 of April 29th, for instance, we can see that it is generated partly by 

 the direct action of the moon with the declination south ascending (a cir- 

 cumstance which is favourable to its development), and partlyby the 

 direct action of the sun with declination north. The evening tide, on 

 the contrary, is connected with the action of the " anti-moon" in the 

 northern hemisphere, and that of the "anti-sun" in the southern. 

 The former, therefore, is a lunar tide compounded with a solar, and 

 the latter is an anti-lunar tide compounded with an anti-solar. The 

 positions of the moon at each quarter are likewise noted, and also at 

 apogee and perigee, and thus it is seen how the sun's angle and the 

 moon's distance separately affect the height of each tide. The method 

 is new, and is very successful. 



