Royal Society. 549 



tween the origin of this membrane and that of the retina. In both 

 cases they arise as a protruded portion of the cerebral mass, being 

 hollow and communicating with the cavity of the parent-cell. In 

 process of time, a gradual separation takes place between them and 

 the parts from whence they arise. They then assutne a pyriform 

 shape, but still communicate with the cerebral cavity. As, however, 

 the nerves become solidified and the separation between them is 

 more fully effected, then no communication can be traced between 

 the two cavities. 



8. "Tide Researches. Fourteenth Series. On the Results of 

 continued Tide Observations at several places on the British Coasts." 

 By the Rev. W. Whewell, D.D., F.R.S. &c. 



Tide observations made at several different parts of the British 

 and neighbouring shores, and in some instances continued for a con- 

 siderable period, having beert discussed by Mr. D. Ross of the 

 Hydrographer's Office, with great labour and perseverance, a brief 

 statement of the results which his labours afford is here presented 

 by Dr. Whewell. 



The discussions here referred to relate to the height of high water, 

 and the variations which this height undergoes in proceeding from 

 springs to neaps, and from neaps to springs. It is found, by ex- 

 amining the observations at 120 places, and throwing the heights 

 into curves, that the curve is very nearly of the same form at all 

 these places. Hence the semi-mensual series of heights at any place 

 affords a rule for the series of heights at all other places where the 

 difference of spring height and neap height is the same. For in- 

 stance, Portsmouth, where the difference of spring height and neap 

 height is 2 ft. 8 in., is a rule for Cork, Waterford, Inverness, Bantry, 

 Arcachan on the French coast, and other places: and the tables of 

 the heights of high water at one of these places suffices for all the 

 others, a constant being of course added or subtracted according to 

 the position of the zero-point from which the heights at each place 

 are measured. 



The series of heights of high water for a semi-lunation also agrees 

 very exactly, as to the form of the curve, with the equilibrium 

 theory. A very simple construction is given for the determination 

 of this curve. The properties deduced according to theory from 

 this construction are, however, in actual cases, modified in a manner 

 which is then described. 



1. The tides in these discussions are not referred to the transit of 

 the moon immediately preceding, but to some earlier transit, namely, 

 the second, third, fourth or fifth preceding transit, it being found 

 that in this way the accordance with the theory becomes more exact. 



2. According to this construction, the difference of springs and 

 neaps would be to the height of neaps above low water springs as 

 10 to 24, a constant ratio for all places ; but in fact this ratio is dif- 

 ferent at different places : and the observations under consideration 

 show that the ratio is smaller where the tide is smaller. 



In consequence of the law of the high water, given alike by the 

 theory and by the observations, the spring high waters are above the 

 meau high water for a longer period than the neaps are below it. 



