August, 1911. 



KNOWLEDGE. 



327 



Diiioniis (the Moa). The first of these — the 

 eggs and remains of which have been found in 

 Madagascar — is generalh' believed to be tlie 

 original of the '" Roc." and certainly lived down 

 almost to historic times. It was a flightless, 

 ostrich-like bird that laid one enormous egg at a 

 time. Specimens ha\e been found measuring 

 IJ inches bv 9-5 inches. In this connection it is 



interesting to note that the Apteryx, a modern 

 flightless bird of New Zealand, about the size of a 

 fowl, lavs, likewise, an egg entirely out of proportion 



to its bulk, being very nearl\- as 



big as that of 



a swan. Doubtless in fl\ing birds the eggs are 

 necessarily prevented from becoming ver\- large, 

 to ensure that the bird does not become too heavy, 

 but in those that are flightless there is no such need. 



I To he coiitiiiiiCii.) 



thp: time of niGii water. 



By J. A. HAKDCWSTLE. 



.\t this time of the year so many people enjoy the sands and 

 the bathing at the seaside, that the time of High and Low- 

 Water is a subject of considerable importance, and the wise 

 man will consult a local tide-table if he wishes to choose the 

 best date for his visit or indeed the best seaside resort for his 

 purpose. The Norfolk coast has long enjoyed a great popu- 

 larity, yet it is more than probable that no one has noticed one 

 great advantage that it possesses, a feature, the loss of which 

 would be more detrimental than the disappearance of the 

 much-vaunted sands. It consists in the particular value for 

 that coast of what is technically called the "establishment," 

 a list of which <iuantities is given in Wliitakcr's Almanac 

 page 68. The value for Cromer is five hours — meaning that 

 High Water occurs there five hours after High Water at 

 London Bridge. 



It is common knowledge that each day the tides occur fifty 

 minutes later, and consequently, in the course of fourteen days 

 they go all round the clock, and the moon also passes from new 

 to full and full to new in fourteen days. Consecjuently if High 

 Water occurs at noon on the day of new moon it will occur at 

 noon also on the day of full, and in fact all the Spring Tides 

 will be high at noon. It is also well known that the tides 

 proceed round the coast and on any one day High Water 

 occurs at a different moment at different ports. Thus, for 

 instance. Spring Tides are high at Aberdeen at 2 o'clock, at 

 Cromer at S o'clock, at Brighton at 12; these hours may be 

 taken as both morning and afternoon since there are practically 

 twelve hours between any two high tides. 



I can well remember my disappointment as a child at 

 hearing again and again of wonderful high tides beating on 

 the sea-wall at Cromer, but they always happened when I was 

 in bed because the Cromer Spring high tides occur at 

 8 o'clock ; but then on the other hand the Spring low water 

 laid bare the best sands and sometimes even showed us the 

 old Church Rock, and these low waters always occurred in 

 the middle of the day. This then is the first point of advan- 

 tage conferred by the " establishment " ; the lowest tides and 

 the best sands happen in the middle of the day. Now at 

 Kamsgate the "establishment" differs from that of Cromer 

 by seven hours and so the Spring flood-tide is in the middle of 

 the day and the best of the sands are bare at 7 a.m. and 7 p.m., 

 which is far less convenient. 



It will, however, be urged that the loss of that particular 

 low tide to the visitor who stays a fortnight is not serious. A 

 week later Cromer will be having low water at 7 or 8 o'clock 

 and Ramsgate at about noon, and though those will indeed be 

 Neap Tides, the difference scarcely matters much. 



But that rejoinder betrays ignorance of one of the most 

 interesting features in the run of the tides, which is called 

 their priming and lagging. 



The following Table gives the times of High Water at 



Cromer for September and October. 1911 : the first column 

 being drawn up on the assumption of a uniform interval of 

 fifty minutes from day to day, the second gives the actual time 

 of High Water — while the tliird gives the actual intervals. 



Let us suppose that the most convenient hour for the 

 summer visitor to ha\e low water is between 12 and 4, while 

 the most inconvenient is between 6 and 10. Our Table gives 

 High Water so we must state it thus : — 



Convenient days High Water from 6 to 10. 

 Inconvenient days High Water from 12 to 4. 



I have marked with a C and an I these days respectively — and 

 one sees at once that there are seven convenient days and 

 only three inconvenient days, while five days are inditTerent, 

 After fifteen days everything repeats itself. The reason is 

 apparent by reference to the third column. Spring tides 

 occur two days after new and full moon, for certain reasons 

 that need not now concern us, and for three or four days before 

 and after the Springs the tidal intervals are very short ; the 

 tides are said to be priming. On the other hand at Neaps 

 the tides lag and the intervals are long. 



If, therefore, the "establishment" is such that Spring tides 

 occur at a favourable hour in the day — you will get perhaps 

 seven very favourable days to three unfavourable — or roughly 

 speaking it is two to one in favour of the tripper finding the 

 sands convenient for him at Cromer. At Brighton it is precisely 

 the opposite, seven unfavourable to three favourable days. 



