\. 



) 1 



^4 



I, 



I 



t: 



\ 



^ 



y 



f 



f 



Sect. IVO 



TIDES. 



117 



allows, for several 



from 





eks or months in succession: for 



such observations we can obtain 



scientific 



results (the effect of the sun, of the moon's parallax, and 



the like), 



23. Besides the changes which arc produced from day 

 to day by the semi-mensual inequality of times and 



heidits, there arc at many 



pla( 



ces 



other considerable 



changes produced between the two tides of the same day 

 hy the dmrnal inequality. 



For example, there are many cases in which the height 

 of high water is alternately lower and higher in successive 



;.i 



24. In this case, if we set off the successive heights of 

 high water as ordinates at equal int<n*vals, and draw a line 

 through their extremities, this hne will have a zigzag form, 



as In fig. 4. 



Heights n.W. 



Fi^. 4. 



-. -f , 



,■ V 



i 



Jan. i, S, 3, 4. 5, r„ 7. % 9. 10, 11, IS, 13. 14, 15, 16, 17. 



J 



--.ra- 



The width of the zigzag increases from nothing to a 

 maximum, and then diminishes to nothing again, general^' 

 in the course of a fortnight ; and so on perpetually. 



25. In consequence of the diurnal ine(iUi-Hy, it some 

 times happens that the afternoon tides are higher than the 

 forenoon tides, or the reverse, for many '.veeks together 



u ^r 



