HARDWICKE'S SCIENCE-GOSSIP. 



>43 



component of gravity. The wing now comes down 

 with velocity sufficient to give the thrust required for 

 horizontal flight. But both soaring and flapping 

 would be impotent without the resolution of the 

 direction of gravity. 



The moment the plane is inclined, it becomes 

 necessary to counteract the component of resolved 

 gravity acting in it, on the downward slant ; and this 

 component carries the plane with it during accelera- 

 tion to the ground before uniform motion occurs. 

 The application of external force to the plane, rever- 

 sing its motion, is attended with difficulty on account 

 of rapidity of its movements and the inertia of the 

 pendent weight. All the impulses must be steady, 

 jolting motion being fatal to success. Care must be 

 taken in carrying our experience of velocity derived 

 from other things into this region. It is not likely 

 that a vigorous man could move his limbs at a higher 

 speed than thirty-five feet per second for a short time 

 at his utmost exertion. These planes greatly exceed 

 this velocity in the lateral motion, the soaring birds 

 moving at times at the rate of 150 feet per second. 



Motion of the planes, therefore, is best derived 

 from their own activities. This can readily be 

 obtained in still air by using fine shot for the weight 

 in oil-silk bag, with a thin neck opening into another 

 placed lower down, and fastened to the corners of 

 the plane by separate strings. The neck should be 

 made to allow two pounds of shot to flow through it 

 in about ten seconds ; as the shot reached the lower 

 bag, the plane would be slanting by drawing on the 

 longer front and shorter rear strings. 



With 150 feet fall, this construction will give 

 motion under the resolution beautifully. Nothing 

 can exceed the graceful curvature of its movements, 

 excepting similar ones made by the soaring birds. 

 As acceleration passes into uniformity, and the total 

 force is expended in the work on air, as the shifting 

 balance inclines the plane transforming the vertical, 

 ample force is on hand in the condensation to resist 

 the downward slanting impulse. If the adjustment 

 is correct, holding the plane on the right incline, 

 horizontal motion will occur until it passes out of 

 sight. More inclination will cause upward slanting 

 direction. If the incline be so great as to throw too 

 much of the resolved gravity into the plane for the 

 forward thrust to cope with, speed will slacken and 

 finally motion to the front will cease and be reversed 

 on the downward slant backwards, and the frail 

 machine become a wreck in an instant by violently 

 striking the earth. I have floated these planes from 

 the lantern of Egment light at the entrance of 

 Tampa bay, on the Gulf coast of Florida, when the 

 air was so still that a handful of down from the 

 breast of a pelican, thrown from the top, would quietly 

 sink along the shaft to the ground. 



To one who is familiar with the soaring birds, and 

 has made a study of their habits, these floating planes 

 present little that is interesting. They imperfectly 



imitate the bird, and do nothing that the birds can- 

 not do better. The latter present a plane with 

 automatic balance as well as a self-acting steering 

 apparatus, and are so plentiful that they can be 

 studied at any time. But the planes serve to explain 

 the wing admirably, and after witnessing their per- 

 formances with none, and either, and all of the 

 contrivances for producing forward thrust, but little 

 more need be said or done explanatory of their 

 functions. 



From the fore-leg of a reptile to this wing is doubt- 

 less a long step, it must needs be. The reptile passes 

 life in the midst of solid, non-elastic resistances ; the 

 bird lives a divided life, part of which is under the 

 dominion of other laws. It copes with fluid elastic 

 pressures when 'it navigates the air, and nature has 

 transformed the creature to meet the changed conditions 

 of its existence. One pair of legs is retained to treat 

 with forces under the dominion of laws which operate 

 in the reptile world in common with man's world 

 where motions are deliberate, impediments plenty, 

 clashing activities found on all sides and the area of 

 translation confined to two dimensions only. The 

 other pair are changed to suit a very different world, 

 where the sea is a hill-side, vertical lines variable, the 

 plane of the horizon perpetually changing, impediments 

 non-existing, velocities high, and the third dimension 

 added to the area of translation. With the organ of 

 flight understood, and the resolving power of planes 

 working on air under the law of fluid pressure com- 

 prehended, there would seem to be no further impedi- 

 ment to the application of the axioms of mechanical 

 science to the problem of air navigation. — American 

 Naturalist. 



MY DRAWING-ROOM PETS. 



By Clara Kingsford. 



Part I. 



SAURIAN REPTILES.— What strange creatures 

 for pets ! No doubt some of my readers will 

 think. And so I should have thought at one time, if 

 I had given them a thought, and no doubt should 

 have thought so for ever and aye, had not my father 

 caught a lizard, whilst it was rapidly gliding across 

 our yard and making for our back door, one bright 

 July morning in 1S80. 



To have attempted a capture by the hand would have 

 been an egregious mistake, for if so caught a lizard 

 is not likely to be retained, for it will usually slip 

 through the fingers, leaving its tail (which is not 

 prehensile and will snap like glass) wriggling in the 

 hand, whilst the body is to be seen quickly retreating 

 into some place of safety. It is said that the tail 

 when broken will grow again, but will never attain to 

 the same length or perfection as the original one ; 

 naturally it will grow if the lizard is young and grow- 

 ing, but I doubt if it will do so in an adult specimen. 



M 2 



