1885. J Analyses oj Books. 687 
The speaker, in describing his late visit to Europe, mentions 
that the supply of Iceland spar fit for making Nicol prisms is at 
an end, the mine being exhausted. Mineralogists would do well 
to search for new sources of this important crystal. He has 
made frequent use of a “ rain-band spectroscope ” for more than 
a year, but only on one occasion has it given a distinct indication 
of rain earlier than the usual atmospheric signs. 
Reviewing the evening after-glows which have been so much 
discussed for some time, Prof. Smith concludes that if dust is 
the source of the phenomenon its origin is cosmic. 
Among the Memoirs here inserted we notice in particular: — 
The Trochoided Plane, by Lawrence Hargrave. The author 
contends that the trochoided plane is the mechanical power al- 
most universally used by Nature for the transmission of force in 
living creatures. As an example he takes the back fin of a fish. 
“ Observation will show that the ends of the spines that keep the 
membrane extended are points in the curve of sines or trochoidal 
wave, and that if they are rotated on their axes in unison, or 
oscillated from side to side harmonically, a series of comple- 
mentary waves will be thrown by the membrane towards the 
tail. This adtion of the fins is best seen when fishes are con- 
fined in a bowl, and appears to be only used whenlthe speed 
does not necessitate the use of the large muscles of the body. 
... If we conceive the adtion of the back fin as thus described 
to be communicated to a series of legs on each side, as in the 
centipede, the effedt will obviously be progression along a sur- 
face ; and if we cut off all the legs but two pairs, separated by 
a distance equal to one wave-length, we have the quadrupedal 
adtion popularly assigned to the giraffe ; if the two pairs are 
only half a wave-length apart, we have the trotting pace of a 
horse ; and the various other paces become clearly dependent on 
the length of the wave used by the animal. The legs and body 
of an alligator or lizard show the connedtion between many- 
legged and four-legged progression. . . . But it is impossible to 
define any hard-and-fast line between any two classes, as the 
more instances of progression we notice the more it is forced 
upon us that they are but links in a chain the two end links of 
which are unknown, whilst any two adjoining links are hardly 
distinguishable. The swinging of the hands and arms, in walking 
and running, is evidence that bipedal is evolved from quadru- 
pedal progression, which to me seems to have developed from 
the trochoidal adtion of a fin. When the amplitude of the waves 
is in a vertical plane, each pair of legs is moved together, and 
the form of the wave is plainly seen in the back of a dog when 
going full split (sic). This method of progression reaches its 
extreme form in the hopping birds. ” 
It seems that it might be interesting to re-examine the loco- 
motion of animals from the author’s point of view. We regret, 
however, to find that the author is seeking to apply his theory to 
