298 
THE REV. W. WHEWELL ON TIDE OBSERVATIONS 
hoped, add considerably to our materials for a closer approximation to a map for the 
whole world, I will not now attempt this, except for the seas to which the observa- 
tions immediately refer. 
18. I have already pointed out the extreme difficulty of forming into a consistent 
and intelligible scheme the tides of the German Ocean*. But as we have now a 
connected series of observations along the whole of its coast, we must make the 
attempt. 
The obvious difficulties may be thus stated. Calling the coast from Calais to the 
north point of Denmark, for the sake of distinctness, the German coast, and consi- 
dering it as opposite to the British coasts, the series of tide-hours on the two opposite 
coasts run thus from south to north. 
British coast. X. XI. XII. XI. X. IX. VIII. VII. VI. V. IV. III. II. I. XII. 
A D B C 
German coast. 11. 12. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. no tide. 
Since the tide-wave in most parts of this series moves in opposite directions on the 
opposite sides of the sea, it is clear that the parts cannot be represented by any mo- 
tion of a wave along a channel. Nor will it answer well to suppose the wave to run 
from C to A along the British coast, and back from A to C along the German coast; 
for the intervals of the lines would, on this supposition, diminish much in passing 
from the space C B to B A, and increase much again in passing from A B to B C ; 
besides which this view does not take into account the disappearance of the tides 
on the coast of Denmark, and the connexion of the tides of Holland with those of 
France. 
It appears that we may best combine all the facts into a consistent scheme, by 
dividing this ocean into two rotatory systems of tide-waves ; one occupying the space 
from B to C, that is, from Norfolk and Holland to Norway ; and the other the space 
from A to B, between the Netherlands and England. In the former space the co- 
tidal lines may be supposed to revolve round the point C, where there is no tide ; for 
it is clear that at a point where all the cotidal lines meet, it is high water equally at 
all hours, that is, the tide vanishes. In the space A B we must suppose similarly a 
tideless centre, as D, about which the cotidal lines revolve. 
This mode of conceiving the progress of the tide does not differ essentially from 
the hypothesis of a progress from C to A and back from A to C, as already men- 
tioned : for on such a hypothesis the motion might be conceived to be resolved into 
two rotatory systems, the wave being supposed to pass from VI. to 7» and from 6. to 
VII., instead of passing from VI. to VII. and from 6. to 7* But this is in reality no 
difference ; for the change really is, that the ridge of the wave passes from the posi- 
tion VI. 6. to VII. 7. ; which is equally well represented by either supposition. 
This hypothesis of two rotatory systems in the German Ocean is recommended 
by its giving the most consistent and probable relations among the cotidal lines and 
* Philosophical Transactions, 1833, p. 188. 
