April 7, 192 1] 



NATURE 



177 



nature of the ocean tides, and these have produced 

 several different charts of cotidal lines. By a 

 cotidal line is meant the locus of all points of the 

 ocean surface at which hig-h water occurs at the 

 same instant. The best known of these charts are 

 those of Whewell and Harris, but quite recently 

 a new set of cotidal lines for the world has been 

 published by Sterneck {Sitz. Akad, Wien, Bd. 129, 

 1920). 



Whewell 's chart was based on the hypothesis 

 that in the Southern Ocean, where the parallels 

 of latitude meet with no great land barriers, 

 powerful tidal waves follow the sun and moon 

 and send off-shoots up the Atlantic, Pacific, and 

 Indian Oceans. Many serious objections have 

 been urged against this. 



Harris's charts are based on the principle of 

 resonance, but the details of the application have 

 been rejected by some high authorities. Harris 

 sought in every ocean for regions which, if com- 

 pletely surrounded by land and not subject to the 

 earth's rotation, would have twelve hours for their 

 longest free period of oscillation; and he always 

 found them ! He then applied the principle of 

 resonance, ignoring the absence of complete land 

 boundaries and the presence of the earth's rota- 

 tion. 



Sterneck 's chart is constructed from the exist- 

 ing observations with the condition that cotidal 

 lines for times differing by six hours shall be as 

 nearly parallel as possible. 



These charts differ very widely from one 

 another. In the Pacific Ocean, for example, 

 Harris places three no-tidal points, whilst 

 Sterneck places six. 



At the present time there is no method by which 

 we can find out what the ocean tides are except 

 that of directly observing them, and it is high 

 time that serious attempts were made to this end. 



If the proposal made by the president of the 

 British Association at Cardiff ever materialises, 

 and a fully equipped oceanographical expedition 

 results, it is very much to be hoped that means 

 will be found of measuring tidal elevations and 

 currents. If trustworthv observations could be 



made at only a few mid-ocean stations, the light 

 they would throw on the great tidal movements 

 would be enormous. And, even if this very desirable 

 object proves impracticable — for it will probably 

 require new methods and instruments — it is under- 

 stood that the expedition would often be in water 

 sufficiently shallow for the methods and instru- 

 ments already developed. Also, the parties of 

 observers which it is hoped might be landed at 

 the most remote islands could obtain tidal records 

 of very great value. 



Hitherto, off-shore tidal observations have been 

 restricted to shallow water, but it has to be con- 

 fessed that in this country very little attention is 

 being paid to the work. No gauge-records of off- 

 shore elevations appear to have been published by 

 any British authority, though trustworthy records 

 are said to have been taken by the French. In this 

 connection we may mention that there is a dis- 

 crepancy of about 40 miles between the charts of 

 cotidal lines for the Irish Sea as published by the 

 Admiralty and those of many foreign authorities. 

 Very few British current-meter observations have 

 been published, though in recent years the Scan- 

 dinavians have worked hard at providing the 

 means of taking them. Bell Dawson has done a 

 notable work in Canadian waters, but where is the 

 band of current measurers in this country that 

 can compare with Nansen, Ekman, Pettersson, 

 Jacobsen, Witting, and Helland-Hansen of the 

 Scandinavian countries? 



Now, although with the instruments that men 

 of other nationalities have developed we may hope 

 to learn a great deal from the suggested expedi- 

 tion whenever it comes into shallow water, yet 

 preparations ought to be in progress for work 

 in deeper water. Quite near to our shores we 

 could have a small expedition which, besides 

 teaching us much about our own tides, would ever 

 strive to observe in deeper and deeper water, 

 devising such modifications of methods and instru- 

 ments as the deeper water required, and im- 

 proving methods and instruments for such depths 

 as had proved practicable at all. It is greatly 

 to be feared that no such efforts arc being made. 



Obitua'ry. 



John Burroughs. 



THIS veteran naturalist and poet died sud- 

 denly while in a train near Buffalo on 

 March 29, within a few days of his eighty- 

 fourth birthdav. He was born, a farmer's 

 son, at Roxbury, New York, on April 3, 

 1837, and had the advantage of a rural 

 education. After about twenty years as 

 school-teacher, journalist. Treasury clerk at 

 W'ashington, and auditor of United States 

 national banks, he bought a farm at West Park, 

 on the Hudson, and spent the rest of his life 

 fruit-growing, observing, and writing. Year after 

 year he wrote delightful and distinctive essays on 

 natural history and country life, which were re- 



NO. 2684, VOL. 107! 



ceived with well-deserved popularity. Mention 

 may be made of "Wake Robin " (1871), "Winter 

 Sifnshine" (1875), "Birds and Poets" (1877), 

 "Locusts and Wild Honev " (1879), " Pepacton " 

 (1881), "Fresh Fields"' (1884), "Signs and 

 Seasons " (1886), and the list might be continued 

 to his "Breath of Life," published a few years 

 ago. 



Burroughs also wrote poems and more than 

 one study of Walt W^hitman, whom he knew inti- 

 mately, and for whom he had an enthusiastic 

 reverence. " Whitman : a Study " is certainly a 

 very remarkable book of its kind, and to the 

 influence of Whitman and Emerson it seems just 

 to say that John Burroughs owed much. 



