CORRESP ONDENCE. 



557 



25 much, with the same ratio of wing or 

 propelling surface to weight ; we should 

 then require simply twenty times more 

 power, or about fifteen horse-power. 



There are, I think, few engineers who 

 will assert such a concentration of power 

 impossible, even when the weight of the 

 man, and fuel for a considerable space of 

 time, are included. Indeed, Strongfellow is 

 said to have, years ago, built an engine and 

 boiler complete which gave a third of a 

 horse-power for a weight of twelve pounds, 

 or weighing only at the rate of five hun- 

 dred and forty pounds for fifteen horse- 

 power. 



Prof. Le Conte shows clearly that with 

 birds " the ratio of weight to strength, and 

 therefore the difficulty of rising, increases as 

 the size or weight " ; but in a machine it is 

 well known that the above ratio decreases as 

 the weight; or, in other words, we can get 

 a hundred horse-power with a much smaller 

 ratio of weight to power than is possible 

 with a single horse-power. 



Even now, using iron and steel and 

 steam, we can concentrate power until we 

 can match the energy of a bird ; but, by the 

 substitution of aluminum, possessing equal 

 strength and weighing only a third as much 

 as steel, why should we not hope to do much 

 more than that ? 



Possibly as a heat-engine the animal 

 machine is more efficient than the best steam- 

 engine, although, nowadays, the " Cornish " 

 can hardly be accepted as a standard of ex- 

 cellence ; but it seems to me the problem is 

 one of concentration of power, rather than 

 economy. Surely Prof. Le Conte must be 

 mistaken in thinking we can not equal the 

 birds in this respect. He underrates the ca- 

 pacity of our engineers. 



The size of a bird is no doubt limited by 

 the strength of bone and muscle, but we are 

 not confined within anything like such nar- 

 row limits. The huge dinosaur had reached 

 Nature's limit of size for a walking-machine ; 

 but compare him with man's conception — 

 the locomotive — weighing eighty tons and 

 giving out the power of more than eight hun- 

 dred horses ! The whale appears to mark 

 Nature's limit of size in marine animals. 

 Compare him with our ocean-steamers, indi- 

 cating fifteen thousand horse-power, and pro- 

 pelled by an instrument vastly more efficient 

 than anything Nature has provided ! 



Why, then, should we be limited in our 

 flying-machine to the weight or size of the 

 largest bird ? Surely, if we can produce in 

 it an equal or greater ratio of power to 

 weight, and can command the use of materi- 

 als strong enough to stand the strain, we are 

 not restricted as to size. 



Nor are we limited in a machine to the 

 birds' way of flying. The leverages of the 

 muscles moving the wings are necessarily 

 short and the strains great, but no more 

 than in a steam-vessel are we bound down 

 by Nature's methods. We may very likely 



be able, in some ways, to improve on her 

 model. 



Even were we to admit Prof. Le Conte's 

 claim that the animal machine can " do more 

 work, with the same weight of machinery and 

 fuel," than anything " we may hope to de- 

 vise," our engineers need not feel discour- 

 aged ; for the power required in rising from 

 the ground is manifestly much greater than 

 that necessary for flight, and why should we 

 not be able to take advantage of this by 

 starting from some elevated point, and slide 

 down and up aerial inclines after the man- 

 ner of a bird ? He then apparently does not 

 need do a great deal of work, and why should 

 a properly constructed machine ? 



The problem is a difficult one, but I can 

 not help thinking Prof. Le Conte at fault in 

 placing its solution among the " impos- 

 sibles." T. W. Mather. 



New Haven, Coxn., December 6, 1SS8. 



DO ANIMALS "PLAT 'POSSUM"? 

 Editor Popular Science Monthly : 



Sir : Walking by a broad ditch, I saw a 

 large, dark-colored snake gliding along the 

 bottom under the water. The crea.ture was 

 coming directly toward me ; but as I paused 

 to observe its markings it stopped, raised its 

 head to the surface, and remained motion- 

 less. Its back was marked with a pattern 

 of criss-cross curves of pale yellow on a 

 ground - tint precisely like that of water- 

 soaked wood. Presently I began to throw 

 little stones, to make it move on, but it did 

 not stir. Meanwhile, the circles caused by 

 my plashing missiles, the ripple -marks on 

 the sandy bottom, the similar curves on the 

 snake's back, and the crooked, lead-colored 

 neck, all combined to pass off the animal for 

 a water-logged stick. It would have been 

 difficult at that moment to have convinced 

 an inexperienced observer that it was a live 

 snake. 



This effect raised the question whether 

 the creature was aware how nearly indis- 

 tinguishable it had become. It is the com- 

 mon opinion that animals "play 'possum " — 

 i. e., remain passive and apparently helpless 

 under attack — for the purpose of safety, while 

 they are entirely alert and would much pre- 

 fer to run away. P>ut is this theory credible 

 when we take into account the immense self- 

 control it demands? And can we credit 

 such a seemingly stupid animal as a snake 

 with sufficient intelligence to select deliber- 

 ately a mode of defense requiring so nice a 

 perception of its own appearance as well as 

 its surroundings? Dr. Abbott thinks that 

 the well-known behavior of the opossum 

 when attacked is due pimply to paralyzing 

 fear, and he supports his theory by many 

 careful observations. If it is true that the 

 opossum faints with terror in the presence 

 of danger, it seems probable that, in the 

 case of other animals, what looks like intel- 

 ligent dissimulation is really due to helpless 



