Dec. 2 1, 1876] 



NATURE 



157 



increasing year by year, and their catch, especially in the early 

 spring, being always very great. 



" VI. The decrease of the fish may be considered as due to 

 the combined action of the fish-pounds or weirs, and the blue- 

 fish, the former destroying a very large percentage of the spawn- 

 ing fish before they have deposited their eggs, and the latter 

 devouring immense numbers of young fish after they have passed 

 the ordinary perils of immaturity." 



As Prof. Baird goes on to remark that there are no measures 

 at command for destroying the blue-fish, even if that were desir- 

 able, and as the blue-fish was once far more abundant than it is 

 at present, while other fishes were also more numerous, I cannot 

 see that I made any mistake in stating that "over-fishing" was 

 unquestionably assigned as "the chief cause" of the decrease in 

 American sea-fisheries. 



Lastly, Mr. Holdsworth says that the question lies between 

 the late Royal Commissioners and myself It was under this 

 belief, holding him as their secretary to be their mouthpiece, that 

 I took some trouble to reply to his first letter. Had any one not 

 in that position challenged my remarks I should, perhaps, have 

 not felt myself bound to give my reasons for the faith that is in 

 me._ He asserts that I have " no practical acquaintance with the 

 subject." Possibly he considers that qualification limited to 

 those who have been named in a Fishery Commission. In such 

 case I certainly have none. He further charges me with using 

 the Index to the Evidence as my " sole guide." Here I must 

 venture to contradict him. I have used that Index, indeed, but 

 much as Norwegian fishermen use the "water-telescope" — to 

 look into the teeming depths of evidence below, unobstructed 

 by the surface ripple of a Report. 



To sum up. Your readers are aware that I originally treated 

 of the Fisheries question as part of a much wider subject on 

 which I felt constrained to speak my mind at a fitting oppor- 

 tunity. I have yet to learn that the Report of a Royal Com- 

 mis.<.ion is beyond the reach of fair and cool criticism, or that it 

 is obligatory on all men to accept that Report as a revelation 

 from supreme intelligence. My criticism of this Report was, I 

 venture to think, not unfair, and it was not made in hasty warmth. 

 Some ten years had passed since I adopted the opinions I hold, 

 and the time had come when, as I thought, I could not help 

 uttering them, nor does it seem to me that an unfitting occasion 

 was offered by a meeting of the British Association. The 

 decision of the question whether there is and has been " over- 

 fishing |' or not is hardly helped by the reiteration of the pas- 

 sage with which my friend ends his rejoinder, 



Magdalene College, Cambridge, Alfred Newton 



December 15, 1876 



Ocean Currents 



Agreeing in the main with Mr. Digby Murray's argument 

 on the subject of ocean currents in Nature (vol. xv. p. 76), I 

 am the more disposed to criticise s-ome of the statements with 

 which it concludes, as put forward too strongly, to say the least. 



I would ask for the "absolute proof" which Mr. Digby 

 Murray supposes to exist, that (i) the upper current rt-turn-trades 

 " flowing from the equator descend again to the surface of the 

 ocean on the polar sides of the calms of Cancer and Capricorn," 

 and (2) "that these equatorial currents, subsequent to their 

 descent on the polar sides of the calms of Cancer and Capricorn, 

 are known as the westerly winds of the temperate zones." That 

 these statements represent the prevailing opinion on the subject 

 I readily admit, but I have ever looked in vain for any convincing 

 arguments in their favour. 



As regards the hypothesis that the trades cross one another in 

 the region of equatorial calms, I may perhaps be permitted to 

 quote some remarks of my own, made two years ago [Symons' 

 Met. Mat;., vol. x. p. 37), since subsequent study has tended to 

 confirm the doubts which I then expressed : — 



" Maury's hypothesis, that the surface trade-wind of one 

 hemisphere becomes the upper-current return-trade of the other 

 (' Physical Geography of the Sea,' sec. 122 to 139) was in all 

 probability originally suggested by the well-known fact that over 

 the southern portion of the N.E. trade a S. E. upper-current 

 prevails, and over the northern portion of the S. E. trade a N. E. 

 Upper- current, though he lays most stress on the arguments 

 which he draws from the greater rainfall of the northern hemi- 

 sphere (sec. 169 to 186), and from Ehrenberg's examination of 

 the African air-dust (sec. 266 to 296). 



" A seaman on approaching the doldrums, commonly notices a 

 current overhead blowing at an angle of about 90' with the 

 surface-trade ; he is aware that this upper-current coincides in 

 direction with the trade on the other side of the doldrums, and 

 that in the calm belt itself, there is an upward motion of the at- 

 mosphere. It is, therefore, not unnatural that he should conclude 

 that the upper-current which he observes is a poleward exten- 

 sion of the opposite trade in the higher regions of the atmosphere. 

 It may also, I think, be admitted that the rapid and suddenly 

 shifting cloud-currents, often observed over the region of the 

 doldrums, are somewhat in keeping with Maury's idea of 

 ' curdle?,' or alternate strips of air. 



" I would suggest that this hypothesis (which many subsequent 

 writers have been surprisingly ready to adopt) may, perhaps, be 

 subjected to a crucial test, if an answer can be given to the fol- 

 lowing query .-—When the south-east trade draws so far to the 

 north as to be deflected into a south-west surface wind, what is 

 the prevalent direction ot the upper-current over the southern 

 portion of the north-east trade? If it runs from south-west it 

 will be difficult to resist the conclusion that Maury is right ; if 

 from south-east it will appear probable that the upper-current is 

 (principally at least) the north-east trade, deflected in the first 

 part of its return course towards the north-west, just as it is in 

 the subsequent part towards the north-east. 



" Perhaps some meteorologist can give a definite answer to this 

 question. The published data for its solution appear rather 

 scanty ; but, so far as my own limited information goes, the 

 observations are generally rather adverse to Maury's theory." 



I would now ask what proof exists that the upper currents 

 from the polar depressions and those from the equatorial depres- 

 sion cross one another in the calms of Cancer and Capricorn so 

 as subsequently to become the trades and anti-trades respec- 

 tively ? Since these upper-currents are understood to meet at 

 the belts of tropical calms and there to descend, it is surely 

 "more reasonable to suppose that their currents intermingle 

 and that their mixed volume is then drawn off north and south, 

 as required to restore the equilibrium of the atmosphere." These 

 are Mr. Digby Murray's words in reference to the equatorial 

 calms, and I fail to see why they will not apply to the calms of 

 Cancer and Capricorn. 



The whole question of the cause of the prevailing south-west 

 and north-west winds of the north and south temperate zones, 

 and the relation which these bear to the polar areas of barome- 

 tric depression, may be regarded as fairly solved by the re- 

 searches of Mr, Ferrel, Prof. J. Thomson, and others. As 

 regards the great intensity of the Antarctic, as compared with 

 the Arctic depression, and the superior force of the we-terlies on 

 its border, there is surely primd facie ground for believing that 

 these are mainly due to superior evaporation in the water-hemi- 

 sphere generally. _ (I say "mainly," because it seems probable 

 that the comparative absence of surface-friction experienced by 

 the atmospheric currents in that hemisphere tends to intensify 

 the Antarctic depression.) That the evaporation from the warm 

 surface-water of the North Atlantic is in excess of that from the 

 relatively cold surface-water of the South Atlantic, may be 

 readily admitted ; but the Atlantic represents, after all, only a 

 small portion of the surface of the globe. Will anyone main- 

 tain that the evaporation from the whole continent of Asia is 

 equal to that which takes place from the corresponding area of 

 the South Indian Ocean ? W, Clement Ley 



Solar Physics at the Present Time 



Having now read the Astronomical Register's more extended 

 account of the November meeting of the Royal Astronomical 

 Society, I found it very confirmatory of Nature's shorter, but 

 more quickly produced, summary of November 23, especially in 

 what was said in the discussion upon Prof, Langley's ( United 

 States) paper on Sun-spots and Terrestrial Climate. Will you 

 kindly allow me to remark : — 



I. I am extremely glad that Sir G. B, Airy is now finding 

 from the deep-soil thermometer observations at Greenwich that, 

 whatever may be the interior temperature of the earth, and the 

 terrific manifestations of it in some special volcanic localities 

 abroad, yet all the remarkable changes and occasional abnormal 

 elevations of temperature in the Greenwich soil come from with- 

 out ; for. Sir, that is precisely one of the earliest conclusions 

 which I deduced for the Edinburgh soil, from the longer series of 

 similar deep-soil thermometers there, and which I had the honour 



