58 



NATURE 



\N0V. 22, 1877 



Rink's book is the one that satisfied our curiosity the 

 least. The sketches of Greenland life by natives, as 

 translated from the " Greenland Journal," are interesting, 

 but they tell us of very little except marvellous escapes 

 from snowstorms and icebergs. The great endurance of 

 suffering, as detailed in some of these stories, demon- 

 strates that heroes can be found even in Greenland ; the 

 sublime spirit of martyrdom seems to breathe in the 

 account of the " Kayakers cast ashore in a snowstorm." 



Scattered through this volume are some sixteen plates, 

 representing Greenland ways of life. These are exact 

 copies of partially coloured drawings executed by natives 

 entirely after their own ideas. The greater number are 

 the work of a seal-hunter living in Kangek, who, falling 

 sick, could not leave his bed. With the drawing which 

 forms plate 16, he wrote to say that increasing illness pre- 

 vented him from doing more, and he ended the letter with 

 " from exhaustion I must cut my letter short, this too will 

 be my future fate," and shortly after he died. 



E. P. W. 



OUR BOOK SHELF 



A Sketch of the Geology of Leicestershire and Rutland' 



By W. J. Harrison. (Shtffield : W. White.) 

 This is a creditable compendium of what is known 

 regarding the geology of the two countries of which 

 it treats. It was originally prepared by its author for 

 White's " History and Gazetteer of the Counties," and has 

 been reprinted in a separate form. It can be had 

 embellished with twelve photographs of various parts of 

 the crystalline nucleus of Leicestershire. These are not 

 particularly successful. Mr. Harrison has done well to 

 put the best of them as a frontispiece. It represents the 

 " coarse ashy slates "- of Charnwood Forest. As a local 

 guide this book may no doubt be useful ; fuller informa- 

 mation can be found in the works which Mr. Harrison 

 cites, and especially in the maps and memoirs of the 

 Geological Survey. 



LETTERS TO THE EDITOR 



[The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communuations. 



The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of com- 

 munications containing interesting and novel facts.'] 



Expected High Tides 



If I may judge from the note published in your issue of 

 November 8 (p. 38), and Mr. Jenkins' letter in the last number 

 of Nature (p. 45), it would appear that the general public are 

 unaware of publications which contain information respecting 

 high tides. 



The Admiralty tide tables contain the time and height of 

 every tide in the year for twenty-four of the principal ports of 

 the United Kirgdom. There are also numerous other tide 

 tables published, which give the heights as well as the times of 

 high water. Amongst these may be mentioned Holden's Liver- 

 pool table?, which contain, besides Liverpool, eight other ports 

 (London irc'uded), and at Liverpool are held in higher esiima- 

 tion than the Admiralty tables, inasmuch as Holden's predictions 

 take into account the effect of the diurnal inequality at Liver- 

 pool, which heretofore has been neglected in the Admiralty 

 tables. There are also published at South Shielf^s, Ainsley's, 

 and at Hartlepool, Pearson's tables, and at Bristol, Ariowsmith's 

 tables (formerly Bunt's), which have deservedly a high reputa- 

 tation for Bristol and the Bristol Channel ports generally. 



Any one who will select from these publications the highest 



perigean spring tides about the time of the equinoxes, and will 

 send them to the papers, can apparently earn for himself the 

 credit of "predicting" high tides. 



The increased range of tide in the Thames of about twenty 

 inches during the last twenty years, is undoubtedly due, among 

 other improvements, to the construction of the embankments, the 

 increased water-way at the bridges at Westminster, and notably 

 at Blackfriars, the improved line of wharfage continually being 

 carried out, and the removal from the Pool of the colliers, which 

 at low water acted as a dam, and prevented the improvement of 

 the bed of the river. 



An overflow in the Thames at above-average spring-tides is 

 now a matter of meteorological circumstances only. It has been 

 observed, I believe, without exception that the overflows have 

 been ciused by a strong northerly wind ; the most disastr^jus 

 overflows, however, have followed a strong south-west wind, 

 changing suddenly to a stiff norlh-west wind. The reason is 

 obvious. An increased amount of tidal water with a south west 

 wind and generally low barometer, is carried from the Atlantic 

 to the northern parts of the North Sea, a sudden change in the 

 wind to north-west brings the whole of this water to the south- 

 ward, with probably litde or no disastrous effects until it reaches 

 the mouth of the Thames, where it meets with the tidal water of 

 the English Channel brought through the Straits of Dover. It 

 then rushes up the Thames, and an additional height is given to 

 the water, amounting sometimes to as much as four feet or more 

 if there is much flood water meeting it, and an overflow is the 

 consequence. I find the effect of a south-west wind on the tide 

 in the Thames, as traced on a self-registering tide-gauge I have 

 placed at Greenwich pier, is to depress the water considerably. 

 The high water of Monday morning succeeding the he?,vy gale 

 of Sunday, November il, was nearly two feet below the pre- 

 dicted height, the extreme pressure of wind, as registered at the 

 Royal Observatory, being 31 lbs. on the square foot. In the 

 middle of October the effect of a south-west gale was still greater, 

 probably owing to its longer continuance, although the registered 

 pressure did not exceed 23 lbs. No overflow need therefore be 

 feared from a continued south-west gale. 



Mr. Jenkins is perhaps unaware that Mr. Saxby has "predicted " 

 high tides for many years, and that on one occasion, I believe 

 in September or October, 1869, the Astronomer- Royal wrote 

 reassuring the public that there was nothing extraordinary in the 

 then forthcoming spring tides to occasion unnecessary alarm. If 

 Mr. Saxby has discovered some law by which he can foretell the 

 direction and force of the wind he will undoubtedly confer an 

 inestimable boon by its publication, but from the following 

 extract from the Times of November 5 he does not appear to 

 claim any such knowledge : — "Capt. Saxby further states : ' If 

 the wind should blow from a northerly quarter on either the 

 7th of November or 22nd of December next, very full tides miy 

 be reasonably expected.' " The spring tides about December 22 

 are slightly below average, and as no overflow has yet occurred 

 with below-average spring tides, but little apprehension need 

 be felt respecting them. 



With respect to the actions of Venus and Jupiter ; although 

 theoretically they cause tides, the Values have hitherto not been 

 evaluated, being almost insensible. 



The high tide of October 26th was entirely due to the northerly 

 wind ; the effect due to the maximum northern declination of the 

 moon is very small in the Thames, and is more than counter- 

 balanced by its effect in decreasing the value of the lunar semi- 

 diurnal tide. 



Mr. Jenkins' statement respecting two great tides revolving 

 through the year exactly six-and-a-half synodic months apart is 

 merely on account of thirteen semilunations being very nearly 

 equal to seven anomalistic months, and therefore the lunar perigee 

 has again the same phase with respect to new or full moon, I 

 may mention that ninety-nine semilunations exceed four years by 

 about eighteen hours only, and also fifty-three anomalistic 

 months by less than thirty-three hours. So that after a cycle of 

 four years the perigean spring-tides fall very nearly on the S'me 

 days of the year. This of course fails to take into account the 

 variations due to' the moon's declination. 



The following table of the heights of the above-average spring- 

 tides for London for next year may be useful not only to river- 

 side owners and dwellers, but also to marine naturalists, who will 

 on these days have unusually favourable opportunities at low- 

 water of engaging in their pursuits. If at such limes the baro- 

 meter should be high the low-water level will be still further 

 depressed. It will also act as a guide to tourists wishing to avail 

 themselves of the best chances of witnessing the bore in rivers, 



