i42 THU CANAI^iAN NATURALIST. [Vol. vL 



density, degree of illumination, and nearness, but also of tactic 

 arrangement, as of a flock of birds or the edge of a cloud of 

 tobacco smoke ! What prodigious difficulties are to be explained? 

 you may judge from two or three sentences which I shall read 

 from Herschel's Astronomy, and from the fact that even Schia- 

 parelli seems still to believe in the repulsion : '' There is, beyond 

 question, some profound secret and mystery of nature concerned 

 in the phenomena of their tails. Perhaps it is not too much to 

 hope that future observation, borrowing every aid from rational 

 speculation, grounded on the progress of physical science generally 

 (especially those branches of it which relate to the ethereal or 

 imponderable elements), may enable us ere long to penetrate this 

 mystery, and to declare whether it is really r.Mtter in the ordinary 

 acceptation of the term which is projected from their heads with 

 such extraordinary velocity, and if not impelled^ at least directed, 

 in its course, by reference to the Sun, as its point of avoidance." 

 "In no respect is the question as to the materiality of the tail 

 more forcibly pressed on us for consideration than in that of the 

 enormous sweep which it makes round the Sun in periJielio in the 

 manner of a straight and rigid rod, in defiance of the law of 

 gravitation, nay, even, of the received laws of motion." " The 

 projection of this ray. ... to so enormous a length, in a single 

 day, conveys an impression of the intensity of the forces acting 

 to produce such a velocity of material transfer through space, 

 such as no other natural phenomenon is capable of exciting. It 

 is clear that if we have to deal her e^ with matter, such as we 

 conceive it, viz., p>ossessing inertia — at all, it must be under the 

 dominion of forces incomparably more energetic than gravitation, 

 and quite of a diffi3rent nature." 



Think now of the admirable simplicity with which Tait's 

 beautiful ''sea-bird analogy," as it has been called, can explain 

 all these phenomena. 



6. BIOLOGICAL RESEARCH. 



The essence of science, as is well illustrated by astronomy and 

 cosmical physics, consists in inferring antecedent conditions, and 

 anticipating future evolutions, from phenomena which have actu- 

 ally come under observation. In biology the difficulties of suc- 

 cessfully acting up to this ideal are prodigious. The earnest 

 naturalists of the present day are, however, not appalled or para- 

 lyzed by them, and are struggling boldly and laboriously to pags 



