8o 



The Museum Gazette 



it is said sometimes lift a small boat and throw it upon the 

 deck of the barge in front of it. To this sudden rise — expe- 

 rienced chiefly at spring tides and in narrow but deep tidal 

 rivers — the name of " bore " or "ager" is given. In some 

 places, in order to prevent damage, it is customary for those 

 down stream to raise the cry "Ware ager " for the benefit of 

 those higher up, who at once look to their mooring ropes, or 

 if in movement, to their rudders. 



Remembering that the moon passes over the earth's sur- 

 face once only in a day, it may seem puzzling why there 

 should occur two tides. What we have said as to the 

 influence of the moon being exerted on large masses of water 

 rather than superficially, may here again help the reader's 

 conception of the facts. The entire mass of the globe, solid 

 as well as fluid, comes under the influence of lunar attraction, 

 but it is the fluid which alone can move its place. Thus 

 when the tide rises, the solid earth as well as the water is 

 influenced, whilst the water alone is seen to respond. The 

 effect of the earth's movement is, however, felt on the opposite 

 side of the globe. The land is, so to speak, drawn away from 

 the water and the latter is left to heap itself up and constitute 

 a tide. Thus it is high water at the same time on opposite 

 parts of the planet and on both sides twice a day. It may 

 perhaps be suggested by some thoughtful reader that if one 

 tide be the result of direct attraction of the water from the 

 earth, and the other of the attraction of the earth from the 

 water, it is scarcely probable that they would be exactly alike 

 in strength. Nor in truth are they; every alternate tide is 

 slightly weaker than its companions. 



When reading about the tides the reader should have at hand 

 a small globe. * He may advantageously make observations 

 on the mass movements of water in any large vessel in 



* A small globe should be part of the equipment of every student. Very 

 neat ones mounted on stand and with a case for protection, may be had of 

 Messrs. Philips, in the Strand, and probably of many others, for the sum of 

 eighteenpence. 



