HALF AN HOUR WITH THE WAVES. 7 



make, and that she has slowly made a little of it 

 between tide and tide, it follows that the wave has 

 to advance further than before to get right under 

 the moon. It is exactly as if we placed the hour 

 and minute hands of the clock, say at twelve. The 

 minute hand will have to go more than once round 

 before it overtakes the hour hand, as the latter will 

 be slowly making its way towards the one o'clock. 

 It is owing to this advance of the moon that the 

 tides recur at intervals of about twelve hours and 

 three-quarters. It is believed that the great tidal 

 wave rises in the southern seas, where, every student 

 of geography knows, there is the greatest area of 

 ocean. There the tide is generally more equable in 

 height, and regular in its occurrence, than in the 

 northern hemisphere. It makes its way into the 

 Atlantic and North Pacific, indenting the coast line, 

 and adjusting its height to the geographical con- 

 ditions it may meet with. How greatly these interfere 

 with tidal effects may be seen by a consideration of 

 the shapes and areas of the Atlantic and Pacific 

 Oceans. Thus, the latter obtains its greatest breadth 

 in an easterly and westerly direction ; whilst in the 

 former the longest diameter is in a northerly and 

 southerly direction. Hence the great tidal wave, 

 entering these vast oceans from the south, is instantly 

 influenced by the form of the basins, or rather, it 

 influences the currents. In the Pacific, we find 

 that the currents are broad and slow, whilst in the 

 Atlantic they are narrow and rapid. In the former, 



