238 Notices of Books. (April, — 
difficult problems in animal mechanics, and to discuss some of 
his views concerning the possibility of flying. A somewhat 
long introduction treats of the various motions possible to dif- 
ferent creatures. It is herein shown that walking, swimming, 
and flying are only modifications of each other. ‘Walking ~ 
merges into swimming, and swimming into flying, by insensible — 
gradations,” and the various differences in the actions are due to 
the fact that the media of support differ in density, earth for 
walking, water for swimming, air for flying. The relation of 
these actions is well shown by the fact that birds and inse¢ts can 
perform them all, while a large number of creatures can both 
walk and swim. ‘‘The subject of flight has never until quite 
recently been investigated systematically or rationally, and as a 
result, very little is known of the laws which regulate it. If 
these laws were understood, and we were in possession of trust- 
worthy data for our guidance in devising artificial pinions, the 
formidable Gordian knot of flight there is reason to believe 
could be readily untied.” Thus early in the book (page 4) does 
our author introduce an evidently pet idea that artificial flight is 
a possibility. The introduction is continued with various dis- 
cussions of the operations performed during walking, swimming, 
and flying; thus we are told that the extremities of animals act 
as pendulums during walking, and describe curves like a figure 
of 8, as also do the bodies of fish in swimming, and the wings 
of birds in flying. Dr. Pettigrew, indeed, claims the discovery 
of the figure-of-8 theory. In the succeeding part of the work 
this theory is applied to, and illustrated by, the progression of * 
various birds, beasts, and fishes. Some beautiful original 
drawings are given to illustrate these motions; we may notice 
particularly those which illustrate the movements ofthe wings 
of the wasp and fly (pp. 139—141). 
Passing on to the subject of aéronautics, our author shows the 
extreme difficulty of the problem of artificial flight to consist, 
among other things, in ‘‘(3rd) the great rapidity with which 
wings, especially insect wings, are made to vibrate, and the 
difficulty experienced in analysing their movements; (4th) the 
great weight of all flying things when compared with a corre- 
sponding volume of air; and (5th) the discovery of the balloon, 
which has retarded the science of aérostation, by misleading 
men’s minds, and causing them to look for a solution of the 
problem by the aid of a machine lighter than the air and which 
has no analogue in nature.” The flightists may now be divided 
into two classes :—1st, those who advocate the use of balloons; 
andly, those who consider that weight greater than the air is 
essential. This second class has two divisions :—‘‘ (a) those 
who advocate the employment of rigid inclined planes driven 
forward in a straight line, or revolving planes (aérial screws) ; 
and (b) such as trust for elevation and propulsion to the vertical 
flapping of wings.” Dr. Pettigrew’s work, although it may not 
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