SCIENTIFIC SIDE-LIGHTS 



80 



ordinary flow of the water. The external ob- 

 jects which, by their mere presence, act 

 upon the organs of the senses; and which, 

 by this means, determine the corporal ma- 

 chine to move in many different ways, ac- 

 cording as the parts of the brain are ar- 

 ranged, are like the strangers who, entering 

 into some of the grottoes of these water- 

 works, unconsciously cause the movements 

 which take place in their presence. For 

 they cannot enter without treading upon 

 certain planks so arranged that, for ex- 

 ample, if they approach a bathing Diana, 

 they cause her to hide among the reeds; 

 and if they attempt to follow her, they see 

 approaching a Neptune, who threatens them 

 with his trident; or if they try some other 

 way, they cause some monster, who vomits 

 water into their faces, to dart out; or like 

 contrivances, according to the fancy of the 

 engineers who have made them. And lastly, 

 when the rational soul is lodged in this ma- 

 chine, it will have its principal seat in the 

 brain, and will take the place of the en- 

 gineer, who ought to be in that part of the 

 works with which all the pipes are con- 

 nected, when he wishes to increase or to 

 slacken, or in some way to alter, their 

 movements. HUXLEY Lay Sermons, serm. 

 14, p. 322. (G. P. P., 1899.) 



391. 



Inscrutable Mys- 



tery of Life Personality. All investiga- 

 tion goes to show that in a mechanical 

 sense the body of an animal is only a very 

 ingenious and effective machine, by means 

 of which the living inhabitant which con- 

 trols it can utilize the energy derived from 

 the food taken into the stomach. The body, 

 regarded as a mechanism, is only a food- 

 engine in which the stomach and the lungs 

 stand for the furnace and boiler of a steam- 

 engine, the nervous system for the valve- 

 gear, and the muscles for the cylinder. How 

 the personality within, which wills and 

 acts, is put into relation with this valve- 

 gear, so as to determine the movements of 

 the body it resides in, is the inscrutable 

 mystery of life; the facts in the case, how- 

 ever, being no less facts because inexpli- 

 cable. YOUNG The Sun, int., p. 3. (A., 

 1898.) 



392. BODY, THE HUMAN, MECHAN- 

 ICAL FUNCTIONS OF Involuntary Closing 

 of the Eye. Consider what happens when a 

 blow is aimed at the eye. Instantly, and 

 without our knowledge or will, and even 

 against the will, the eyelids close. What is 

 it that happens? A picture of the rapidly 

 advancing fist is made upon the retina at 

 the back of the eye. The retina changes 

 this picture into an affection of a number of 

 the fibers of the optic nerve; the fibers of 

 the optic nerve affect certain parts of the 

 brain; the brain, in consequence, affects 

 those particular fibers of the seventh nerve 

 which go to the orbicular muscle of the eye- 

 lids ; the change in these nerve-fibers causes 



the muscular fibers to change their dimen- 

 sions, so as to become shorter and broader; 

 and the result is the closing of the slit be- 

 tween the two lids round which these fibers 

 are disposed. Here is a pure mechanism, 

 giving rise to a purposive action, and strict- 

 ly comparable to that by which Descartes 

 supposes his water- work Diana [see BODY OF 

 MAN, 390] to be moved. But we may go fur- 

 ther, and inquire whether our volition, in 

 what we term voluntary action, ever plays 

 any other part than that of Descartes's en- 

 gineer, sitting in his office, and turning this 

 tap or the other, as he wishes to set one or 

 another machine in motion, but exercising 

 no direct influence upon the movements of 

 the whole. HUXLEY Lay Sermons, serm. 14, 

 p. 335. (G. P. P., 1899.) 



393. BOMBARDMENT BY MOLECULES 



Expansion and Contraction Explained. 

 According to this theory, which is known as 

 the Kinetic Theory of gases, we are to fig- 

 ure the molecules of a gas as flying in 

 straight lines through space, impinging like 

 little projectiles upon each other, and strik- 

 ing against the boundaries of the space they 

 occupy. I place a bladder, half filled with 

 air, under the receiver of the air-pump, and 

 remove the air from the receiver. The blad- 

 der swells. According to our present the- 

 ory, this expansion of the bladder is pro- 

 duced by the shooting of atomic projectiles 

 against its interior surface. When air is 

 admitted into the receiver, the bladder 

 shrivels to its former size; and here we 

 must figure the discharge of the atoms 

 against the outer surface of the bladder, 

 driving the envelope inwards, causing, at 

 the same time, the atoms within to concen- 

 trate their fire, until finally the force from 

 within equals that from without, and the 

 envelope remains quiescent. All the impres- 

 sions, then, which we derive from heated air 

 or vapor are, according to this hypothesis, 

 due to the impact of gaseous molecules. 

 Thus the impression one receives on enter- 

 ing the hot-room of a Turkish bath is 

 caused by the atomic patter there main- 

 tained against the surface of the body. 

 TYNDALL Heat a Mode of Motion, lect. 5, p. 

 118. (A., 1900.) 



394. BONDAGE OF FACT Science Miist 

 Master Details. The bondage under which 

 all true science lies to fact the necessity of 

 groping among the detail of little and com- 

 mon things this is a hard lesson for the 

 human intellect to learn conscious as that 

 intellect is of its own great powers of its 

 own high aims of its own large capacities 

 of intuitive understanding. But it is a 

 lesson which must be learned. There are no 

 short cuts in Nature. Her results are al- 

 ways attained by method. Her purposes 

 are always worked out by law. So must 

 ours be. For our bodies and our spirits are 

 both parts of the great order of Nature ; and 

 our wills can attain no end, and can ac- 



