319 



SCIENTIFIC SIDE-LIGHTS 



{-toe. 



usion 



flying animal has ever been formed on the 

 principle of buoyancy. Birds and bats and 

 dragons have been all immensely heavier 

 than the air, and their weight is one of the 

 forces most essential to their flight. Yet 

 there is a real impediment in the way of 

 man navigating the air and that is the ex- 

 cessive weight of the only great mechanical 

 moving powers hitherto placed at his dis- 

 posal. When science shall have discovered 

 some moving power greatly lighter than 

 any we yet know, in all probability the 

 problem will be solved. But of one thing 

 we may be sure that if man is ever des- 

 tined to navigate the air it will be in ma- 

 chines formed in strict obedience to the me- 

 chanical laws which have been employed 

 by the Creator for the same purpose in 

 flying animals. ARGYLL Reign of Law, ch. 

 3," p. 101. (Burt.) 



1555. ILLUMINATION OF OCEAN BY 

 PHOSPHORESCENT ANIMALS To give an 

 example of the extent to which the illumina- 

 tion due to phosphorescent organisms may 

 reach, I may quote a passage from the wri- 

 tings of the late Sir Wyville Thomson: 



" After leaving the Cape Verde Islands 

 the sea was a perfect blaze of phosphores- 

 cence. There was no moon, and altho the 

 night was perfectly clear and the stars 

 shone brightly, the luster of the heavens 

 was fairly eclipsed by that of the sea. It 

 was easy to read the smallest print, sitting 

 at the after-port in my cabin, and the bows 

 shed on either side rapidly widening wedges 

 of radiance so vivid as to throw the sails 

 and rigging into distinct lights and shad- 

 ows." HICKSON Fauna of the Deep Sea, 

 ch. 2, p. 26. (A., 1894.) 



1556. ILLUSION AT SEA Empty Cap 

 and Coat Assume Guise of Engineer. I was 

 lying in my berth in a steamer listening to 

 the sailors holystone the deck outside, when, 

 on turning my eyes to the window, I per- 

 ceived with perfect distinctness that the 

 chief engineer of the vessel had entered my 

 stateroom, and was standing looking 

 through the window at the men at work 

 upon the guards. Surprised at his intrusion, 

 and also at his intentness and immobility, I 

 remained watching him and wondering how 

 long he would stand thus. At last I spoke ; 

 but getting no reply sat up in my berth, and 

 then saw that what I had taken for the 

 engineer was my own cap and coat hanging 

 on a peg beside the window. The illusion 

 was complete; the engineer was a peculiar- 

 looking man, and I saw him unmistakably; 

 but after the illusion had vanished I found 

 it hard voluntarily to make the cap and 

 coat look like him at all. JAMES Psychol- 

 ogy, vol. ii, ch. 19, p. 101. (H. H. & Co., 

 1899.) 



1557. ILLUSION DUE TO RELATIVE 



SENSATIONS Opposes, as Heat and Cold, 

 Combine in a Contradiction. Another stri- 

 king example is that of our sense of the 

 temperature of objects, which is known to 



be strictly relative to a previous sensation, 

 or more correctly to the momentary condi- 

 tion of the organ. Yet, tho every intel- 

 ligent person knows this, the deeply root- 

 ed habit of making sensation the measure 

 of objective quality asserts its sway, and 

 frequently leads us into illusion. The well- 

 known experiment of first plunging one 

 hand in cold water, the other in hot, and 

 then dipping them both in tepid, is a start- 

 ling example of this organized tendency. 

 For here we are strongly disposed to accept 

 the palpable contradiction that the same 

 water is at once warm and cool. SULLY 

 Illusions, ch. 4, p. 65. (A., 1897.) 



1558. ILLUSION OF ABSENCE OF 

 LIFE Earth at Few Miles' Distance Seems a. 

 Dead World. When [astronomers] declare 

 that the moon is uninhabited because they see 

 nothing moving, they are singularly deceived 

 in the value of telescopic testimony. At some 

 miles high in a balloon, with a clear sky 

 and beautiful sunshine, we distinguish with 

 the naked eye towns, woods, fields, mead- 

 ows, rivers, roads; but we see nothing 

 moving, and the impression felt directly (I 

 have often experienced it in my aerial voy- 

 ages) is of silence, solitude, and the ab- 

 sence of life. Living beings are no longer 

 visible, and if we did not know that there 

 are harvest-men in the fields, flocks in the 

 meadows, birds in the woods, fish in the 

 waters, there is nothing to make us realize 

 their existence. If, then, the earth seems 

 like a dead world when seen from only a few 

 miles' distance, what is it but illusion to 

 assert that the moon is truly a dead world, 

 because we view it at 120 miles or more? 

 for it is only exceptionally that we can use 

 the highest magnifying powers, and in gen- 

 eral we do not apply to the observation of 

 the moon powers exceeding a thousand. 

 What, then, can we see of life at such a, 

 distance? Assuredly nothing, for forests, 

 plants, cities, all would disappear. FLAM- 

 MARION Popular Astronomy, bk. ii, ch. 6, p. 

 148. (A.) 



1559. ILLUSION OF MOVEMENT 



Stationary Train Thought To Be in Motion 

 Sensation Due to Mental Inference. 

 There is an illusion of movement of the op- 

 posite sort with which every one is familiar 

 at railway stations. Habitually, when we 

 ourselves move forward, our entire field of 

 view glides backward over our retina. 

 When our movement is due to that of the 

 windowed carriage, car, or boat in which we 

 sit, all stationary objects visible through the 

 window give us a sensation of gliding in 

 the opposite direction. Hence, whenever we 

 get this sensation, of a window with all ob- 

 jects visible through it moving in one direc- 

 tion, we react upon it in our customary way, 

 and perceive a stationary field of view, over 

 which the window, and we ourselves inside 

 of it, are passing by a motion of our own. 

 Consequently when another train comes 

 alongside of ours in a station, and fills the 



