754 



THE POPULAR SCIENCE MONTHLY. 



chief interest of Dr. Pettigrew's book for 

 thoughtful readers will consist in the skill- 

 ful way he strikes through those diversities 

 of movement and medium which are in- 

 volved in the three forms of progression, 

 and brings out the principles that are com- 

 mon to all. " We are apt," he says, " to 

 consider walking as distinct from swim- 

 ming, and walking and swimming as dis- 

 tinct from flying, than which there can be 

 no greater mistake. Walking, swimming, 

 and flying are, in reality, only modifications 

 of each other. Walking merges into swim- 

 ming, and swimming into flying, by insen- 

 sible gradations. The modifications which 

 result in walking, swimming, and flying, are 

 necessitated by the fact that the earth af- 

 fords a greater amount of support than the 

 water, and the water than the air. That 

 walking, swimming, and flying, represent in- 

 tegral parts of the same problem, is proved 

 by the fact that most quadrupeds swim as 

 well as walk, and some even fly, while many 

 marine animals walk as well as swim, and 

 birds and insects walk, swim, and fly, indis- 

 criminately." 



The problem thus becomes interesting 

 from the unity of its fundamental laws, but 

 for the author it has more than a specula- 

 tive interest ; it has a scientific importance 

 as furnishing conditions for solving the 

 problems of artificial progression. 



Upon this point he remarks : " The his- 

 tory of artificial progression is essentially 

 that of natural progression. The same 

 laws regulate and determine both. The 

 wheel of the locomotive and the screw of 

 the steamship apparently greatly differ from 

 the limb of the quadruped, the fin of the 

 fish, and the wing of the bird ; but, as I 

 shall show in the sequel, the curves which 

 go to form the wheel and the screw are 

 found in the traveling surfaces of all ani- 

 mals, whether they be limbs (furnished with 

 feet), or fins, or wings. 



" It is a remarkable circumstance that the 

 undulation or wave made by the wing of 

 an insect, bat, or bird, when those animals 

 are hovering before an object, and when 

 they are flying, corresponds in a marked 

 manner with the track described by the 

 stationary and progressive waves in fluids, 

 and likewise with the waves of sound. 



" Of all animal movements, flight is in- 



disputably the finest. It may be regarded 

 as the poetry of motion. The fact that a 

 creature as heavy, bulk for bulk, as are many 

 solid substances can, by the unaided move- 

 ments of its wings, urge itself through the air 

 with a speed little short of that of a cannon- 

 ball, fills the mind with wonder. Flight (if 

 I may be allowed the expression) is a more 

 unstable movement than that of walking 

 and swimming, the instability increasing as 

 the medium to be traversed becomes less 

 dense. It, however, does not essentially 

 differ from the other two, and I shall be 

 able to show, in the following pages, that 

 the materials and forces employed in flight 

 are literally the same as those employed in 

 walking and swimming." 



These passages, foreshadow the charac- 

 ter of Dr. Pettigrew's book. He works 

 out the principles of animal locomotion as 

 a further step in the progress of artificial 

 locomotion, by which the theoretical issues 

 in the practical. After an elaborate analy- 

 sis of the anatomical and dynamical condi- 

 tions of flight, he goes into the question of 

 its imitation by art, and points out the con- 

 ditions on which he thinks the problem may 

 be ultimately solved. Here, of course, he 

 launches into an untried field, abounding 

 with difficulty, and open to a diversity of 

 opinions. Already a brisk controversy has 

 sprung up in the London journals over his 

 theory of flight, and the question of prece- 

 dence in its elucidation between the French 

 and the English ; but, whatever may be its 

 merits, the interest of Dr. Pettigrew's con- 

 tributions to the question in the present 

 volume will remain unaffected. We should 

 not omit to state that the volume is profuse- 

 ly and beautifully illustrated with original 

 cuts and plates. 



Prang's Natural History Series op Col- 

 ored Chromos. For Schools and Fami- 

 lies. Classified by N. A. Calkins ; 14 

 large Plates ; 192 Cards. Price of full 

 set, $10. J. W. Schermerhorn & Co., 

 Agents, 14 Bond Street, New York. 



Mr. Prang, having achieved fortune and 

 fame in the cultivation of the chromo-litho- 

 graphic art in the department of fancy pict- 

 ures, has at length turned his attention to 

 education, and applied it to the illustration 

 of objects of natural history. A large num- 



