November 5, 1914] 



NATURE 



255 



without any mathematics. The surface of the ocean, 



apart from waves and tides, is at any time a figure 



of equilibrium answering to the speed of rotation at 



the time, more oblate when the speed is greater, less 



oblate when it is slower. Let us imagine that the 



■rhosphere also is at some time a figure of equilibrium 



iswering to the speed of rotation at that time. If 



e speed remained constant, the lithosphere would 



tain this figure, and the matter within it would 



remain always in the same configuration without 



having to support any internal tangential stress. Now 



- uppose that the speed of rotation gradually diminishes. 



he surface of the ocean will gradually become less 



nd less oblate. The lithosphere also will gradually 



come less oblate, but not to such an extent as to 



ake it a figure of equilibrium answering to the 



iminished speed of rotation, while the matter within 



; will get into a state of gradually increasing internal 



mgential stress. The effect on the distribution of 



nd and water will be that the depth of the ocean 



ill gradually diminish in lower latitudes and increase 



. higher latitudes, the latitudes of no change being 



5= 16' X. and S. 



The internal tangential stress in the matter within 



.e lithosphere may increase so much that it can no 



nger be supported. If this happens a series of local 



actures will take place, continuing until the litho- 



here is again adjusted much more nearly to a figure 



f equilibrium, which will be less oblate than the 



iginal figure. The effect on the distribution of land 



nd water will be that the depth of the ocean will 



crease rather rapidly and spasmodically in lower 



titudes and diminish in higher latitudes. 



Accordingly the kind of geological change 



hich the theory of tidal friction would lead 



- to expect is a sort of rhythmic sequence, 



volving long periods of com'parative"" quiescence, 



arked by what Suess calls "positive movements of 



.e strand," in the higher latitudes, and " negative 



ovements " in the lower, alternating witih compara- 



;\ely short periods of greater activity, marked by 



>e of the land around the poles and subsidences in 



Te equatorial regions. It is for geologists to say 



hether the facts known to them are consistent with 



r.is description or not. A. E. H. Love. 



The Age of a Herring. 



Ix the issue of Nature for September 17 Prof. 

 D'.\rcy Thompson states that he is unable to persuade 

 -imseif of the validitv: of Dr. Hjort's conclusions based 

 :pon the methods of determining the age of herrings 

 by a study of their scale-rings. 



It is, of course, impossible to attempt to deal in a 



o:w words with all the evidence brought forvv-ard in 



ivour of these methods in recent years by different 



biologists, and we must, with regard to the herring, 



refer to our published papers,* where argiaments are 



^iven in favour of the primary assumption that the 



ge of a herring may be determined by counting the 



ings seen on its scales. The facts supporting this 



ssumption are briefly : — 



(i) For \oung individuals (up to age of three years) 



le results of age determinations by means of the 



-cale-rings correspond with the results obtained by 



1 Hjort, "Report on Herring Investigations until January, igio," Publ. 

 •■: CitcoHst., No. 5^. Copenhagen, 1910. 



Hjon and Lea, "Some Kesults of the Intemat. Herring Inv., i<)07-ii. 



uhl. de Circonst., Xo. 61. Copenhagen, 1911. 



Hjon, " Floctnations in the Great Fisheries of Northern Europe," 

 'apports et Proces-Verhaux, vol. xx. Copenhagen, 1914. 



Lea, " On the Methods used in the Herring Investigations," Publ. tie 

 ■-irconst., No. 53 Copenhagen, 1910. 



Lea, ".\ Study on the Growth of Herrings." PubL de Circonst., No. 61. 

 Copenhagen, ign. 



Lea, '_' Further Studies concemine the Methods of calculating the Growth 

 :f Herrings," Publ. de Circonst., No. 66. Copenhagen, 1913. 



plotting frequency curves for the length measurements 

 of the individuals. 



(2) Scale examination of small herrings continued 

 with short inter\-als during all seasons showed that 

 the formation of the so-called winter rings took place 

 during the winter, while the formation of the so-called 

 summer belts commenced in the spring and continued 

 during the summer months. That the summer belt 

 is small at the commencement of the formation in May, 

 while it is large on the completion of the formation 

 in the beginning of autumn, has been proved by 



' observations carried on during four years. Regarding 

 the older fish, it has been difficult to proceed in the 

 same manner as for younger fish, as the frequency 

 curves fail to give any hints as to the age groups 

 represented in a sample, while, on the other hand, 

 the fishing season for the old herrings does not extend 

 over all seasons of the year. The following facts 

 point to the correctness of the assumption that the 

 conditions here are strictly homologous to the condi- 

 tions as regards the younger fish. 



(3) Among the Norwegian herrings a great many 



5 4 5 6 7 S 9 10 II 12 13 14 15 16 17 18 



Fig I. — Showing the captures of Norwegian mature herrings for eight 

 successive years, arranged in percentage frequency curves according to 

 the number of rings on the scales (the nombos along the absossa 

 denoting the ring gioups). 



individuals had an abnormally small third summer 

 belt on their scales. Herrings showing this abnormality 

 have been ver}^ frequently observed during all the 

 )-ears from 1907 to 1914, but while the scales of these 

 herrings in the year 1907 had only one summer belt 

 outside the abnormal one in 1908, they showed two 

 summer belts, and so on until the winter 1913-14, 

 when they had seven summer belts outside. Thus 

 these herrings, so easily distinguishable by their 

 abnormality, have during the seven years of observa- 

 tion annually formed one summer belt on their scales, 

 each belt being separated by a winter ring from the 

 preceding and succeeding belts. 



(4) By scale investigations on the Norwegian spring 

 herrings (spawning herrings), carried out during the 

 years from 1907 to 19 14, results are obtained the main 

 points of which are given in Fig. i. This diagram 

 is based upon all the material from 1907-13, while 

 for 19 14 part of the material was not worked up when 

 the diagram was constructed (still the curve for this 

 vear is based upon more than 2000 individuals). 



NO. 2349, VOL. 94] 



