ii6 



NATURE 



[Dec. 7, i8; 



The path of the shadow defined by these numbers differs sen- 

 sibly from that given in Nature, vol. xv. p. 65. It passes to 

 the north of Nimrud instead of the south. 



With the permission of Mr. Hind, I a'so transmit the follow- 

 mg hst of solar ecHpses, computed by him, of which the results 

 are preserved in the manuscripts of the Royal Observatory : — 



Royal Observatory, Greenwich, December 5 



Negretti's Reversible Thermometer and the Arctic 

 Expedition 



Capt. Nares presents his compliments to the editor of 

 Nature, and requests him to correct a mistake which Capt, 

 Nares inadvertently made in his ofScial report to the Admiralty 

 concerning the late Arctic expedition, and which has been re- 

 printed in Nature, 



In obtaining some deep-sea temperatures, which pioved the 

 existence of a sub-stratum of water warmer than that at the 

 surface, the instruments used were the reversible thermometers of 

 Negretli and Zambra, not Casella's. The Casella thermometer 

 was used on other occasions, but not at the time referred to, 



H, M, S, Alert, Portsmouth, November 30 



The Arctic Expedition 



Two or three considerations have led me to believe that 

 possibly the recent Arctic Expedition has not been so fortunate 

 as might have been wished, and that the same amount of fore- 

 sight, courage, and energy, expended on a similar expedition 

 another year might be attended with much more satisfactory 

 results. 



The considerations referred to are these : — 



Fifty years ago Sir Edward Parry traversed a distance of some 

 hundreds of miles in sledges upon what he at first supposed to be 

 the main pack ; but on finding that as fast as he travelled north- 

 wards he was drifting to the south, he concluded what he had 

 mistaken for the main pack, was after all only a loose floe of 

 immtnse extent. 



Now in 1872, on the return of the American expedition, we 

 were all given to understand that an open Polar Sea existed where 

 instead is now found a sea of ancient ice. All testimony con- 

 curred in pointing to this open sea. The climate was warmer 

 than further south; birds were seen fl>ing north; a creeping 

 herbage flourished, and bright flowers were not absent. Musk 

 oxen, rabbits, and lemmings also abounded. Now these Polaris 

 explorers were neither mendacious nor stupid ; and it seems to 

 me that it is rather premature to set down their inference from 

 all they observed as a mistake. 



Now, sir, my theory, true or false, new or old, is this : — This 

 Pal^KOcrystic Sea is really a vast floating island of ice ; say 500 

 miles in diameter. Just like the ice in a pail or on a pond, it 

 mtlts in the hot weather at the edges, and then, disengaged from 

 the land, it floats hither or thither, according to the direction 

 of the prevalent winds or currents. If this theory be correct, it 

 accounts for Parry's disappointing journey, for the inferences 

 based on the Polaris observations, and for the otherwise unac- 

 countable (act that the ice encountered by the recent explorers is 

 undoubtedly ancient. The fact that the vast floe showed no 

 sigr,s of drifting away last summer only shows that the wind was 

 unfavourable, or that this northernmost Greenland coast, when 

 once the ice {is stranded, does not easily relinquish its grasp. 

 Possibly if a Hecla had attempted in 1876 what was impracti- 

 cable in 1827, or if an Alert had tried in 1827 what has just 

 proved a failure, both enterprises would have succeeded. 



Next time two opposite routes must be' undertaken simi 

 taneously, of which one will fail and the other succeed. 



Wordsworth Donnistiiorpe 

 17, Porchestcr Terrace, W, 



The Age of the Rocks of Charnwood Forest 



In reference to the letters which have appeared in Natu 

 (vol. XV. p. 97) allow me to say, in the first place, that I neit! 

 attached, nor intended to attach, any discred t to Mr. Wo 

 ward's very useful manual for the statements it contains in re 

 ence to the age of the Charnwood Forest Rocks. On the oti 

 hand, I am gratified to find that so competent an observer as t 

 Rev. T. G. Bonney concurs with me in the view " that there 

 not a particle of evidence for their Laurentian age," This v 

 the special point of my letter; and I fail to see that Prof, Gree 

 hypothetical inferences from certain sections at Mark field 

 which he fears that he has kept no record) are of much value 

 the question. Prof. Green, however, admits that the great m 

 of these rocks give no evidence of Laurentian age. 



As regards what may be the respective limits of " Cambriai 

 and "Silurian" rocks that is another question. I am qu 

 aware that Sedgwick claimed formations as " Cambrian " whi 

 are not so recognised by the Geological Survey, nor by 1 

 majority of authors, continental as well as British ; for examp 

 M. Barrande, To which of the series of formations belongi 

 to the Cambrian system of Sedgwick the forest rocks are to 

 referred I am not prepared to say ; but I think it must 

 allowed that the negative evidence founded on the absence 

 fossils ought to have some weight in favour of the view that th 

 are referable to the horizon of the " Cambrians" of the Geo 

 gical Survey rather than to that of the Llaudeilo or Carad 

 beds, 



Mr, Bonney's comparison of the forest rocks with those of t 

 volcanic series of the Lake District is very suggestive ; nor 

 the correspondence of the strike of the beds in both distri( 

 without its weight, where every circumstance ought to be tak 

 into consideration in question of such uncertainty. It woD 

 also be very desirable if some general understanding could 

 arrived at regarding the respective limits of the Cambrian a) 

 Silurian systems. There are scarcely two authors who adopt i 

 same view on this subject. Theoretically it may be a matter 

 small consequence ; but practically it gives rise to confusi* 

 amongst geologists and amongst students of geology. As this 

 the age of " conferences " why should not a conference of Palre 

 zoic geologists meet and lay down a frontier line for the tv 

 kingdoms, which would last, perhaps, for a generation, at 

 until the "instinct of nationality" crops up and brings ( 

 another conflict between the inhabitants of Cambria and Siluri 

 and their allies respectively? EDWARD HULL 



Geological Survey Office, Dublin, December 4 



"Towering" of Grouse, Partridges, &c. 



Most of your readers doubtless know what is meant by tf 

 towering of game-birds ; but, for the sake of those who do no 

 I will begin by describing the facts. When a partridge, for i 

 stance, is hit while on the wing by a few pellets of ihot — perh; 

 only by one or two — the flight may continue for a variatjle ch 

 tance ; but, if the bird is a " towerer," a slight irregularity soo 

 begins to show itself, after which the flight rapidly becomf 

 more and more laboured, till eventually the bird ceases ii 

 onward motion altogether. The direction of the flight no' 

 changes from the horizontal to the perpendicular, and with 

 rapid fluttering sort of action the bird rises to a variable heigh! 

 when all motion suddenly ceases, the animal falls like a '■"' 

 and the sportsman then knows that when he finds his p. 

 it will be lying dead on the exact spot where he "ma 

 down," 



Before proceeding to state the cause of these curious move 

 ments, I should like to draw more prominent attentior 

 fact?, first, that the time after receiving the wound durinj 

 horizontal flight continues is variable ; second, that the jukk^ 

 variation are tolerably definite, a bird never towering until it 1; 

 flown some distance after being shot, and never flying any ver 

 great distance before towering ; and third, that the height 

 which the bird rises is also variable, this height being sonieti 

 only 1 or 2 feet, and at other times 40 or 50. 



