258 DR. PETTIGREW ON THE MECHANISM OF FLIGHT. 



The Heron (Plate XIV. fig. 38), Seamew, Lapwing (Plate XI Y. fig. 29), and Owl (Plate 

 XIV. fig. 30) supply examples of the second class, where the wing, as compared with the 

 body, is very ample, and where consequently it is moved more leisurely and less energe- 

 tically. The Albatros (Diagram 18 d, p. 253) and Pelican furnish instances of the third 

 class, embracing the heavy-bodied, long-winged birds. 



^ The Duck (Plate XIV. fig. 37), Pigeon (Plate XIV. figs. 33 and 40), Crow (Plate XIV. 

 figs. 41 and 43) and Thrush are intermediate, both as regards the size of the wing and 



the rapidity with which it is made to oscillate. 



The Albatros (Diagram 18 d, p. 253), Swallow, Eagle, and Hawk (Plate XV. fig. 60) 

 furnish instances of sailing or gliding birds, where the wing is ample, elongated, anymore 

 or less pointed, and where advantage is taken of the weights the body and the shape 

 of the pinion to utilize the air as a supporting medium. In these the pinion acts as a 

 long lever *, and is wielded with great precision and power, particularly at the shoulder. 



The Might of the Albatros compared to the Movements of a Compass set upon Gimbals 

 A careful examination of the movements in skimming birds has led me to conclude that 

 by a judicious twisting or screw-like action of the wings at the shoulder, in which the 

 pinions are alternately advanced towards and withdrawn from the head in a manner analo- 

 gs t o what occurs at the pelvis in skating without lifting the feet, birds of this order can 

 not only main am the motion which they secure by a few energetic flappings, but, if ne- 

 cessary actually increase it, and that without either bending the win. or leaW the 



t*— e 



~* ~v,c*„x^ b 



fo ™ard and backward action of the pinion referred to in 

 no ay int., feres, I may remark, with the rotation of the wing on its long axis, the pinion 



ITST^F ff ;Ti d Cl ° Wn UP ° n ^ ^ dui ^ «*™£n, and redacted 

 "fie Z % 1h ° ff th : Whld during flexl0n - The te - s "extension" and 



sn k n^of tS /r e ' aTe ^ USGd ln the S6nSe in Which 1 em P%ed them when 



ZX ft in v W " S : baCWdS> ° r thG —' - d *™ *«le to side or 



I a D ram 19, p. 259), the one corresponding with the long axis of the body 



* Ail rant ages possessed by lonq Pinion* Th» I mM 



m the frd (pointed out by Mr Wenh 1\ t W„ ™ ^ « m0St effecti - « levators and propellers, 



from the fad (point,,! out by Mr.Wenham) that at 1 ° hi ** aS eleVat ° rS ™ d P r0 P ellerS 



becomes transferred to the front edge of the pinion It — !'i • ^ ° bliqUe inddences > the s«PP<>rting effee. 

 two-bladed screw is tantamount to its entire eireie of 11 !>n "V ^ ^ ***** ^^^ "" ° f ^ 

 George Cayley upwards of fifty years a-o '"The stabilit ' 1 " P rinci P le was announced by Sir 



below the point of suspension, is 'aided by a remarkable cill^^T' "^ ^ '** *■*" ° f «""* ^ 

 ncute angles with the current, it appears* that the centre of 2 T «P e ™«* alone could point out. .„ w , 



:- _*_ ^ ,_ . , . . . I centre of reszstance in the sail does not coincide with the centre of 



In very 



*».o cwuace, uul us cunsiaerao/i/ in front of it 4« fh 1 r wiuiauo wiui me centre ui 



coincide when the current becomes perpendicular to\L X^ ^l^ ^"^ de ° reaSeS ' these centres approach, and 

 wards removes the centre of sunnort bphinri «. i_/u~ x L P ane ' ience an >' heel of the machine backwards or for- 



■Nicholson 



wards removes the centre of support behind or before th* If \ *" 7 



*h« the S peet, attained by tie L is ,^" ^ „° 7??"^ 



enormously increased, the support afforded by the air to th ' r i ^ iMW "* °^ * W flWy ^' w * tim 



mented. Tlii. is proved by the rapid flight of *kimmin» or s l Ti l™ f ° rmed b ' V the ^ * /, "* w, ' w "'" 

 and , ry leisurely. The same principle supports the skater as he^l * ^ *"** ™ m0Ved at Io " g interVaIS 

 flat Btone projected along the surface of still water The velo it 7 lmpetU0Usl y over "«««« ice, and the thin 

 not giving the supporting particles time to separate 7 movement ^ either case prevents sinking by 



