208 THE POPULAR SCIENCE MONTHLY, 



wanderers upon the ocean so far from their native habitat, and I find 

 that they nearly all exhibit to a greater or less extent the same curi- 

 ous characteristics. Here the observant mariner with a smattering of 

 science may find something to cogitate upon. 



Light, heat, sound, etc., are said to be effects produced upon the 

 living organism through the medium of appropriately developed or- 

 gans by as many different modes of motion, whereby the animal is 

 brought into conscious connection with surrounding objects, the effect 

 diminishing in a progressive ratio as the distance of the object in- 

 creases. Of these special organs there are said to be five in number 

 which are essential to the well-being of all perfectly developed animals. 

 But may there not be other analogous modes of motion, producing 

 analogous effects upon the living organism, whereby the animal is 

 brought into conscious connection with surrounding objects, and by 

 or through which it has a sense of the locality or direction of such 

 objects as are essential to its well-being to seek or avoid? Admit- 

 ting this, suppose a flock of birds have started on one of their migratory 

 excursions, guided mainly by this sense of direction, in pursuit of some 

 distant object. Then let us suppose that in their flight they pass 

 obliquely, but unwittingly, into another higher stratum or current of 

 air moving with great velocity in some other direction, but toward the 

 ocean. The flock would necessarily become very much scattered, and 

 in the confusion a portion of them would be carried unconsciously 

 out to sea, beyond the range of their sense of direction — having lost 

 which, they fly at random and at ease, exerting just sufficient effort to 

 sustain themselves in the air ; while another portion of the flock, keep- 

 ing within the limit of their sense of direction, will exhaust all their 

 strength vainly endeavoring to reach their object against a violent 

 wind. 



So intimately associated with this sense of direction is their instinct 

 of self-preservation in avoiding the presence of man, that while the 

 one is in abeyance, the other, in the absence of anything to arouse it, 

 remains dormant. This, I believe, is the true meaning of the preter- 

 natural tameness exhibited by the birds on the Galapagos Islands men- 

 tioned by Darwin. 



From the peculiar properties of air in its relation to heat, the at- 

 mosphere has a tendency to form itself into heterogeneous strata, more 

 or less inclined to the horizon ; each stratum having a horizontal motion 

 independent of the others — a fact the significance of which, I think, 

 is frequently lost sight of by meteorologists, more especially by cyclo- 

 nologists. That some of the higher strata of the atmosphere have an 

 independent horizontal motion, the velocity of which is often income 

 parably greater than anything we experience in the lower stratum, is 

 evident not only from the appearance in mid-ocean of birds, but of 

 insects hundreds of miles from land, and apparently as lively as if 

 they were in their own native haunts. I have seen grasshoppers at 



