536 



SCIENCE. 



evolved improved methods of progression. The most of 

 them have returned to the quadrupedal condition, if we 

 may conceive the four-footed baboons to have arisen in 

 this manner. As to whether any of them have gained the 

 perfected bipedal condition, it is perhaps best to make no 

 assertion. Those who hold that man had an ape-like pro- 

 genitor, must accept this view. 



There are other mammals with partially bipedal habils. 

 These compromise the jumping animals, the kangaroos, 

 jerboas, etc. But in these cases there has been no speciali- 

 zation of the fore-limbs. They have simply become partly 

 aborted. The bear also, through its plantigrade feet, and 

 perhaps its climbing habit, has gained imperfect bipedal 

 powers, and a grasping habit with its fore limbs. But 

 there has been no specialization of these limbs. They 

 continue true walking organs. 



In the reptilian world other instances of bipedal habits 

 present themselves, developed in still another manner. 



The animals thus organized are all creatures of a van- 

 ished age — the huge Deinosaurian reptiles presented to 

 us in the geological record. These creatures may have 

 gained their specialization of form through the same cause, 

 though not in the same manner, as the giraffe gained its 

 special formation. Many of them lived by browsing on 

 the foliage of trees. And these, instead of developing an 

 elongated neck, like the giraffe, probably obtained their 

 food by a partially climbing process. Their fore limbs 

 clasped the tree trunk, while their weight rested on the 

 hind limbs and the tail. In this manner they were able to 

 reach the desired food. 



A long continuance of such habits would produce, 

 through selection, a specialization of the fore limbs. To 

 become efficient organs for grasping tree trunks, they 

 must have become inefficient walking organs. Through 

 this specialization the fore limbs seem to have become 

 small and comparatively weak, the hind limbs large and 

 powerful. To look at the remains of these creatures now, 

 as preserved for us in the rock strata, it seems as if a 

 quadrupedal motion must have been very awkward and in- 

 efficient ; while their habit of erecting themselves on their 

 hind legs, may have rendered a bipedal motion easy and 

 natural. Professor E. U. Cope says of them : " some have 

 chiefly squatted, some leaped on their hind legs like the 

 kangaroo, some stalked on erect legs like the great birds, 

 with their small arms hanging uselessly by their sides." 

 Yet when we consider the great size of these reptiles, 

 which comprise the huge Iguanodon and Megalosaurus, 

 the Hadrosaurus of our New Jersey marl, and other such 

 gigantic creatures, we may well imagine that they pres- 

 ented an appearance widely different from that of any ex- 

 isting creatures. To see animals thirty feet in height and 

 huge in proportion, to whom our elephant would be -a 

 mere pigmy, stalking about erect on their hind legs, would 

 certainly be an astonishing spectacle. Yet such a view 

 was very probably presented by that bizarre world of the 

 past which time has swept away. 



These Deinosaurian reptiles, with their peculiarities of 

 structure, their hollow bones, and their thiee-toed feet, 

 presented certain strong affinities to the great land birds 

 of modern times. So close, indeed, that some have con- 

 jectured that these large wingless birds, such as the 

 Ostrich, are direct descendants of the Deinosaurs. In 

 this claim there are no powers of flight to be explained, 

 yet the possession of feathers by the ostrich seems a fatal 

 obstacle to the hypothesis. Feathers are a highly spec- 

 ialized form of dermal covering. They are specially 

 adapted to purposes of flight, and we can imagine for 

 them no other use which the less specialized hairs or 

 scales would not have subserved. We are therefore dis- 

 posed to conclude that any animals possessed of feathers 

 must have gained them through powers of flight in them- 

 selves or their ancestors ; and that the resemblances in 

 organization above mentioned arose from similarity in 

 modes of progression, and not from hereditary connection. 



How, then, was the lurther step in the process taken ? 



The primitive hairy covering being gained, how did hairs 

 develop into feathers, how were the imperfect bipeds 

 among land animals succeeded by the perfect bipeds 

 among flying animals, and how did motion upon the 

 earth develop into motion through the air? It certainly 

 did not arise as a result of leaping habits. We cannot 

 imagine the spring of a kangaroo as so advantageously 

 aided by an accidental conformation of the fore limbs, as 

 to produce a natural selection of this conformation. If 

 these leaping animals habitually sought to assist their 

 flight by a motion of the fore limbs, then any membra- 

 neous expansion or special thickness of hairy covering 

 would be advantageous. But none of those now existing 

 have such a habit, and without it their leap could never 

 become a flight. 



( To be continued!) 



THE NEW COMPRESSED AIR LOCOMOTIVE. 



On the 13th ultimo a trial of a new engine built 

 by the Baldwin Works, Philadelphia, took place on 

 the Second Avenue Railroad, the result of the trial 

 being on the whole satisfactory. Compressed air as a 

 motive power for railway engines has been repeatedly 

 tried already in this country and in Europe. At 

 Paris and Nantes the Mekarski Air Engine has at 

 different times been used with more or less success, at 

 Glasgow. Mr. Scott Moncrieff has labored perseveringly 

 to demonstrate the superiority of compressed air over 

 steam for locomotive purposes, while in June last year 

 Col. Beaumont produced (in London) an engine which 

 was thought at the time to have eclipsed its predecessors 

 in point of efficiency and small working cost. The 

 " success," however, of these engines has been so very 

 undecided, and the advantages they presented in point of 

 cleanliness, and absence of smoke and noise, have been 

 so counterbalanced by the cost of compressing and stor- 

 ing the air, that as yet we have heard of no line of rail- 

 road or tramway being successfully worked by compress- 

 ed air. 



Comparing the data obtainable from these engines with 

 the result of the late trial, we find a decided superiority 

 in the efficiency of the American engine which possesses 

 several new and important features, and is the result of 

 long experience and study of the subject by the inventor 

 and patentee, Mr. Thos. Hardie, the Pneumatic Company's 

 Chief Engineer. 



A short description of the engine and its trial may not 

 be uninteresting to our readers. In length and weight 

 it is as nearly as possible the same as an average Elevated 

 Railroad engine, the pait usually reserved for the boiler 

 being in this case occupied by the receivers for contain- 

 ing the air, four in number and of unequal lengths, hav- 

 ing an aggregate capacity of 460 cubic feet, in which air 

 is stored at a pressure of 600 lbs. per square inch. In- 

 side the cab is a small boiler (the consumption of coal in 

 which is nominal) through which air from the receivers 

 is passed before being allowed to enter the cylinders. 

 An automatic throttle valve on the supply pipe of this 

 boiler regulates the pressure at which the cold air enters 

 the boiling water. The air being thus heated expands 

 and the pressure is of course considerably augmented, 

 and in this hot, moist condition it passes into the cylin- 

 ders, having a far larger percentage of efficiency than if it 

 were allowed to do so in a cold, dry condition. There is 

 thus by this means a great saving in the quantity of air 

 consumed. The system of drawing air from the reser- 

 voir at a low pressure and expanding it by heat until it 

 attains a working pressure of from 100 to 130 lbs. per 

 square inch is, we believe, entirely novel, and in this 

 respect the engine differs altogether from Col. Beaumont's 

 machine, in which air was admitted to the cylinders at 

 its initial reservoir pressure— 1000 lbs., and then quickly 

 cut off. 



In a former engine built by the Pneumatic Company 



