J::ly, 1890. THE YOUNG NATURALIST. 



121 



TIDING AT EASTER-TIDE. 



BY CHARLES H. H. WALKER. 



Easter presenting the long-desired opportunity for a few days 

 holiday, no very mature deliberation was needed to decide us in favour 

 of a trip to the Isle of Man — a decision materially strengthened by 

 the knowledge of the prevalence of spring tides at that particular 

 season. Nor was much difficulty experienced in forming a jovial 

 quartette, the doings whereof being set forth in this and the following 



pages. There was Dr. M. , an indefatigable student of sponges, 



Mr. R. , with predilections emphatically in the direction of things 



slimy, though erstwhile not unlovely ; Mr. F. , with no tastes 



whatever in particular, and, finally, our unworthy self, who desired 

 nothing better than a further acquaintance with the rocky shores of 

 Mona's Isle. 



Shore collecting is interesting at all times, more so during the 

 periods of spring tides, and perhaps it may be pardonable to very 

 briefly explain the meaning of the term. We need scarcely remind 

 the reader, that, though the sun and moon exert together an attractive 

 force upon the earth, the waters of the ocean, being matter susceptable 

 of change of shape, are more subject to the influence than the land it- 

 self. The sun, by reason of its greater distance, exerts far less power 

 upon the water than the moon, which is so much nearer. When the 

 attractive force of both luminaries acts in a straight line, i.e., when 

 they are either in conjunction or opposition (new moon and full moon), 

 we naturally have a period of greatest attraction, and hence a spring 

 or high tide. And it naturally follows that when the waters are thus 

 gathered together in huge volumes at two opposite sides of the earth, 

 extremely low ebb must prevail at those parts of the globe most dis- 

 tant from the points of flood tide. Thus it is possible then to reach a 

 much lower zone and to collect animals that inhabit deeper water. 

 By analogous reasoning, when the lines of attraction of sun and moon 

 form a right angle, two such opposing forces must of necessity dimin- 

 ish the power of either, and, as a natural consequence, neaps, or 

 low tides prevail, with the accompanying slight ebb. Now by a 

 special stroke of good luck, high springs were due at Easter, and, 

 moreover, as flood tide occurred at or about noon, it was possible to 

 work two tides daily. What could be more alluring ? 



