1868. | The Modern Aspects of Physical Science. 329 
species, in one or other of which it may become so changed in 
appearance, that its identification is possible only by a close com- 
parison between the many links which connect its most abnormal 
forms with those in which it is ordinarily found. 
I have often felt the want of a rationale of this kind, in 
admiring the colour-patterns of butterflies, and have endeavoured to 
trace a kind of homology between their respective constituents. 
For a long time the case seemed hopeless; but opportunities 
having been afforded me of examining a moderately large number 
of Rhopalocera from most parts of the world where they abound, 
many apparent anomalies were found to be so only because inter- 
mediate forms had not previously been known to me. Thus, for 
instance, I have ventured to speak of the red spot at the anal angle 
of the hind-wing of our British Swallow-tailed Butterfly as a form of 
the “blush.” British butterflies alone considered, this must appear 
to be simply fanciful; but any one who will examine even a limited 
number of species of the large genus Papzlio will, I think, be 
satisfied that the red spot on the hind wing of P. Machaon is a 
modification of the richer tinting of the pale ground-colour, such 
as may be seen in its more ordinary form in P. Zagreus (Doubleday), 
and in a striking intermediate form in P. Iswara (White). 
I have only touched on the elementary portion of the subject; 
more minute details must be reserved for another occasion; but I 
venture to hope that the present very imperfect account of an 
attempt to classify the colour-patterns of butterflies may not be 
uninteresting to their admirers, and may lead to further investi- 
gations by more able observers. 
IV. THE MODERN ASPECTS OF PHYSICAL SCIENCE. 
Ir we examine with thoughtful deliberation the aspects of Physical 
Science as they are now presented to our mental vision, we arrive at 
the conclusion that much uncertainty surrounds them, and we feel 
that with the advance of knowledge we shall have to modify many 
a pet hypothesis and, possibly, to abandon some favourite theories 
which have held their position by the weight of the great names 
by which they have been supported. 
We have before us ten works, each one of them excellent in its 
class,* and in their entirety fairly representing the conditions of the 
* 1, ‘The Elements of Natural Philosophy; or, an Introduction to the Study of 
the Physical Sciences.’ By Charles Brooke, M.A., M.B., F.R.S. Churchill. 
2. ‘Heat considered as a Mode of Motion. By Jobn Tyndall, F.R.S. 
Longmans. 
3. ‘Faraday as a Discoverer.’ By John Tyndall. Longmans. 
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