282 



NATURE 



\Feb. 12, 1874 



'aquelle j'avais recours est a pen prcs identiqile i' la sienne.. - . . 

 Je m' einpres5e de satisfaire a cette demande legitime, et je laisse 

 entiurement la priorite sur moi, a M. Petti^rew relativement a la 

 question aiusi restreiiite." {Comptcs Rendus io-c May 16, 1870, 

 p. 1093.) 



The next point which Mv. Garrod takes up is the "induced 

 currents " of the wing. I state that " the efficiency of the wing 

 is greatly increased by the fact that when it ascends it draws a 

 current of air up after it, which current, being met by the wing 

 during its descent, greatly augments the power of the down- 

 stroke. In like manner, wlien the wing descends, it draws a 

 current of air down after it, which, being met by the wing during 

 its ascent, greatly augments the power of the up-stroke." This 

 is simply a statement of fact, and if Mr. Garrod causes a natural 

 or artificial wing to vibrate he will find that the wing takes a 

 greater catch of the air when a down- and up-stroke or an up- 

 and down-stroke are made in rapid succession, than when a 

 single stroke is made either in the one direction or in the other. 

 This point becomes especially clear if a large artificial wing be 

 constructed on the insect type and made to vibrate in a horizon- 

 tal direction. If such a wing have its anterior margin slightly 

 elevated and made to travel from right to left of the operator it 

 draws after it a current of air which, being met by the wing when 

 it is reversed and made to pass from left to right, acts as an 

 autumn breeze to a kite. The wing literally flies on the current 

 wliich it creates. It ascends at each thrust and carries the hand 

 of the operator with it. Similar remarks are to be made of the 

 tail of the fish. It is in this way that the back air and luck 

 laiih-r are utilised, ar.d herein lies the excellence of the elastic 

 reciprocating screw, as found in Nature, and as contra-distin- 

 guished from the rigid rotatory screw employed in navigation. 



Mr. Garrod, adducing no proof in refutation of this and similar 

 experiments, states " that these waV/i-t-i/ «;;7v«/i are of no real 

 service in flight, because in their production there is as much force 

 lost as there may be gained from their subsequent employment on 

 the reversal of the action of the wing, if the bird's body has not 

 advanced sufficiently far to be in each stroke beyond the range of 

 their action, which is probably the case." On what authority 

 does Mr. Garrod make this assertion ? When a bird flies in 

 still air, the wing of necessity must vibrate. The quicker it 

 vibrates the more marked the reaction obtained from the air, and 

 the greater the elevating and iiropclling power. The induced 

 cuireiils powerfully contribute to this reaction from the fact 

 that the wing and the air are both moving, and moving in oppo- 

 site directions. This, as explained, is a matter of experiment, and 

 can readily be verified. 



Lastly Mr. Garrod attacks my views on muscular movements. 

 Here again he adduces no counter-proof, and, adhering to the 

 old doctrine, contents himself by saying, *' \\'e are not ashamed 

 to say that such has always been and still is our idea." This is 

 not saying much. He takes exception to my statement that 

 muscles have a centripetal or shortening power and a centrifugal 

 or elongating power. Can he inform me how the left ventricle of 

 the heait opens after a vigorous contraction, in M-hicli all the 

 blood contained in the ventricular cavity is ejected and the 

 ventricle converted into a solid muscular mass, if not by a spon- 

 taneous doni^ation of all its fibres ? 



Edinburgh, Jan. 27 J. JSelt. Pettigrew 



Specific Gravity of Sea-water 



In reference to Mr. Strachan's letter in Nature, vol. ix. 

 p. 183, calling attention to the discrepancy between Dr. Frank- 

 land's results and my own, permit me to slate that they were 

 not obtained from the same series of samples, and that the figures 

 given by Dr. Frankland were, I believe, obtained by tlie use of 

 a balance on shore, and also that from the way in which his speci- 

 mens were packed, they were not liable to any aj)preciable loss 

 by evaporation. They were not, however, taken Irom that part 

 of the North Atlantic which was examined during the time that 

 I was on board the Porcupine in 1S69, to which altfne my obser- 

 vations refer. My own results were obtained, as stated on p. 503 

 of "The Depths of the Sea," by delicate ghass hydrometers, so 

 graduated that the sp. gr. could easily be read to the fourth deci- 

 mal place. Two instruments only were employed for the 105 

 observations made, and though they gave identical results, I had 

 no opportunity of comparing their indications with the re- 

 sults obtained l)y a balance from the same specimen of water. 

 I may remark here, however, that though the absolute results 

 may not be quite correct, the relations between the sp. gr. of 

 surface, intermediate, and bottom waters, pointed out on p. 505 



of "The Depths of theSea," as well as the range of variation, are 

 probably very near the truth, since the same instruments were 

 employed in all the determinations, aod at the end of the series 

 they indicated the same as at the commecicemenl, when placed 

 in a test solution, which was preserved To ■ the purpose of de- 

 tecting possible variations in the instruments themselves. 

 Clifton, Bristol, Jan. 17 Wm. Lant Carpenter 



THE LINNEAN SOCIETY 



WE regret to hear of an unpleasant event which 

 took place at the meeting of the Linnean So- 

 ciety on Thursday last (5th inst). So far as we have 

 been able to gather the particulars they are as follows. 



When the usual minutes had been read at the com- 

 mencement of the meeting, a Fellow of the Society rose 

 in his place and endeavoured to propose a motion 

 reflecting upon the conduct of the President at the pre- 

 ceding meeting. The President (Mr. George Bentham, 

 F.R S.) ruled that the Fellow was out of order and that 

 his motion could not be put, and requested the would-be 

 mover of it to sit down in his place. In spite of frequent 

 calls to order, however, this gentleman persisted in his 

 endeavours to bring forward his grievances, and to ad- 

 dress the meeting. At last Mr. Bentham. finding that 

 his efforts to preserve order were vain, and that the mover 

 of the motion (who had given no sort of notice of his 

 intentions) was backed up by a body of clamorous 

 friends assembled specially for the purpose, quitted the 

 chair and left the meeting-room, followed by the Secretary 

 and all the other members of the Council present. 



As the chair of the Linnean Society can only be taken 

 by a member of Council, the meeting thus came to a pre- 

 mature end, much to the disappointment of those who 

 had assembled to hear Mr. W. K. Parker read his paper 

 on the osteology of the woodpeckers. 



We regret to have to add that, in consequence of this 

 untoward event, Mr. Bentham has tendered his resigna- 

 tion as President of the Society. Bat we trust that the 

 Fellows who caused the disturbance will, upon reflection, 

 feel that however much they might have considered them- 

 selves aggrieved by the President's decision at the pre- 

 vious ineeting, they were not justilied in the course they 

 pursued. In all meetings the decision of a chairman upon 

 a point of order is held to be final, at all events for the 

 occasion. More especially should this be the case in a 

 learned society assembled for the discussion of scientific 

 problems, and not for vulga.r wranglings and disputes 

 upon immaterial subjects. 



We trust therefore that an ample apology will be offered 

 to the President by these gentlemen, and that he will be 

 induced to retain his chair until the approaching anniver- 

 sary meeting offthe Society, when he had already given 

 notice of his intention not to accept re-nomination. The 

 great services which j\lr. Bentham has rendered to Science 

 generally and to the Linnean Society in particular, are 

 too well known to the readers of Natjrk to render it 

 necessary for us to descant upon them in these columns. 

 The Linnean Society has just acquired a new and most 

 convenient abode in the apartments at Burlington House, 

 recently provided for it by the liberality of the 

 country, and it would be a great misfortune if disunion 

 should succeed in marring the work of those who are now 

 endeavouring to make the Society still more useful and 

 more prosperous than it has been in pa-t times. 



POLARISATION OF LIGHT* 

 IV. 



THE phenomena exhibited by selenite are also produced 

 by other crystals, but the facility with which jjlates of 

 the former substance can be obtained, causes them to be 

 generally used in preference to others. There is, however, 

 a peculiar class of crystals, of which quartz, or rock 

 crystal, is the most notable, which gives rise to effects dif- 

 ferent from those hitherto described. 



