15 



SCIENTIFIC SIDE-LIGHTS 



Adaptations 

 Adjustment 



teeth fitting into each other, so that the 

 whole shall form one continuous sur- 

 face or web. This is a correlation of 

 growth between one particular kind of 

 feather and one particular member of 

 the body, which, in all Birds capable 

 of flight, is constant, and amounts to 

 a universal law. Now let us contrast 

 this with another correlation of growth 

 which is equally constant. On the side of 

 the head of all birds there is a patch of 

 feathers of peculiar structure, with fine and 

 slender shafts, and with the lateral fila- 

 ments not hooked together as in the other 

 case, but, on the contrary, always separated 

 from each other the whole series forming 

 a fine and open network spread over the sur- 

 face which they cover and protect. These 

 feathers cover the orifice of the ear, and are 

 called the auriculars. They are correlated 

 with the curious passages, the finely hung 

 clapper-bones, and all the elaborate mechan- 

 ism of that organ. Such are the internal 

 correlations. But they are intelligible only 

 when considered in the light shed by other 

 correlations which are external. The wing- 

 feathers, with close continuous webs, are 

 correlated to the laws by which the passage 

 of air may be prevented ; the auricular feath- 

 ers, with open unconnected webs, are corre- 

 lated to the laws by which the passage of 

 sound may be rendered easy. The one set of 

 feathers is adapted to the active function 

 of evoking and resisting atmospheric pres- 

 sure by striking strong, yet light and elastic 

 blows, upon the air ; the other set of feath- 

 ers is adapted to the passive function of 

 allowing the free access of the waves of 

 sound into the passages of the ear. These 

 are but a few examples out of millions. 

 Throughout the whole range of nature the 

 system of internal correlation is entirely 

 subordinate to the system of external corre- 

 lation. ARGYLL Reign of Law, ch. 5, p. 151. 

 (Burt.) 



75. ADJUSTMENT OF ORGANS FOR 

 MUSICAL EFFECT A Natural Violin The 

 Mole-cricket. If one walks in the meadows 

 along a little brook on a fine June evening, 

 he will often hear a long-sustained note, 

 even, subdued, and pleasant, which vibrates 

 powerfully without swelling or diminishing, 

 somewhat like that of the nightingale in 

 Haydn's " Toy Symphony." A cautious ap- 

 proach will enable us to sec a mole-cricket 

 sitting, apparently motionless, in front of 

 its hole in the ground. More careful ex- 

 amination proves that the short wing-covers 

 are in a state of continual vibration, pro- 

 ducing friction as they move ; and this it is 

 which causes the sound. The microscope 

 shows that minute and delicate teeth are 

 placed at regular intervals along a vein on 

 one of the wing-covers; when these are 

 struck at a certain rate by a vein on the 

 other wing, they emit a whirring note of a 

 definite pitch. One vein acts as the bow, the 

 other as the string of a violin ; the mole- 

 cricket is a violinist, and can therefore hold 



on its note as long as it will. WEISSMAN 

 Heredity, vol. ii, p. 34. (Cl. P., 1892.) 



76. ADJUSTMENT OF SOUL TO THE 

 NON-EXISTENT A Breach of Continuity- 

 Would Violate All Analogy of Nature. 

 Now if the relation thus established in the 

 morning twilight of man's existence between 

 the human soul and a world invisible and 

 immaterial is a relation of which only the 

 subjective term is real and the objective 

 term is non-existent, then, I say, it is some- 

 thing utterly without precedent in the 

 whole history of creation. All the analogies 

 of evolution, so far as we have yet been able 

 to decipher it, are overwhelmingly against 

 any such supposition. To suppose that dur- 

 ing countless ages, from the sea-weed up to 

 man, the progress of life was achieved 

 through adjustments to external realities, 

 but that then the method was all at once 

 changed and throughout a vast province of 

 evolution the end was secured through ad- 

 justments to external non-realities, is to do 

 'sheer violence to logic and to common 

 sense. FISKE Through Nature to God, pt. 

 iii, ch. 10, p. 189. (H. M. & Co., 1900.) 



77. ADJUSTMENT OF VISION TO 

 DISTANCE Adaptation Automatic and Un- 

 conscious. Mark, now, the superiority of 

 the eye. In its normal condition this won- 

 derful organ possesses a power to which no 

 optical instrument of human construction 

 can show the remotest parallelism that of 

 adjusting itself to differences of focal dis- 

 tance. Thus, if I close one eye, and hold up 

 my finger between my other eye and the 

 clock at the far end of the room, I cannot 

 see both of them distinctly at the same 

 time, because, as they are at different dis- 

 tances from my eye, their pictures on my 

 retina cannot both be distinct. But, with- 

 out moving either my head or my eye, I can 

 so " focus " my eye on either as to see it 

 distinctly, the other becoming hazy. This 

 we all constantly do without the least 

 knowledge of the mechanism by which it is 

 effected: and all that the most careful and 

 refined investigation has revealed to the 

 physiologist is that the focal adjustment is 

 made by a change in the curvature of the 

 crystalline lens; its curvature being in- 

 creased when the rays that fall upon it are 

 more divergent, because proceeding from a 

 nearer object; and being diminished when 

 the rays, proceeding from a more distant 

 object, are less divergent so as in each case 

 to bring them to a focus on the retina. This 

 change of curvature is produced, it is be- 

 lieved, by the action of the ciliary muscle 

 which surrounds the lens; but how that ac- 

 tion is called forth we do not know. Indeed, 

 we are quite unconscious that we are put- 

 ting it into contraction. I simply deter- 

 mine, "I will look at the clock," or, "I 

 will look at my finger," and my eye adjusts 

 itself accordingly. If, on the other hand, I 

 were to look with a telescope, first at a 

 watch -face a few feet off, and then at a 



