395 



SCIENTIFIC SIDE-LIGHTS 



Life 

 Light 



ceivable minuteness. The pleasures we de- 

 rive from the harmonies of color and of 

 sound, altho mere sensations, do correctly 

 represent the movement of undulations in a 

 definite order ; whilst those other sensations 

 which we know as discords represent the 

 actual clashing and disorder of interfering 

 waves. Thus it is that in breathing the 

 healthy air of physical discoveries such as 

 these, altho the limitations of our knowl- 

 edge continually haunt us, we gain never- 

 theless a triumphant sense of its certainty 

 and of its truth. ARGYLL Unity of Nature, 

 ch. 4, p. 94. (Burt.) 



1928. LIGHT A RESULT OF COR- 

 RELATION The Retina Attuned to Ethereal 

 Vibrations. Light itself, therefore, is dis- 

 covered to be merely a relative term a 

 word, in short, denoting nothing but an ex- 

 ternal correlation between the retina and 

 vibrations of a certain kind and quality. 

 Now what is the language which Professor 

 Tyndall is constrained to use in explanation 

 of facts so difficult of conception? It is the 

 language of mechanism, of mental purpose 

 and design. " It is not," he says, " the size 

 of a wave which determines its power of 

 producing light ; it is, broadly speaking, the 

 fitness of the wave to the retina. The ethe- 

 real pulses must follow each other with a 

 certain rapidity of succession before they 

 can produce light, and if their rapidity ex- 

 ceed a certain limit, they also fail to pro- 

 duce light. The retina is attuned, if I may 

 use the term, to a certain range of vibra- 

 tions, beyond which, in both directions, it 

 ceases to be of use." These are indeed won- 

 derful correlations which reveal to us fit- 

 tings and adjustments of which we had no 

 previous conception; but they give us no 

 glimmering, even, of knowledge as to the 

 physical causes which have " attuned " a 

 material organ so as to catch certain ethe- 

 real pulsations in the external world, and 

 to make these the means of conveying to 

 man's intelligence the enjoyment and the 

 power of sight. ARGYLL Reign of Law, ch. 

 5, p. 153. (Burt.) 



1929. LIGHT, ARTIFICIAL Primi- 

 tive Methods Lasted Till Recent Times 

 The Link-boys of London. The first illumi- 

 nants were probably torches made of resin- 

 ous woods, which will give a flame for a 

 considerable time. Then the resin exuding 

 from many kinds of trees would be collected 

 and applied to sticks or twigs, or to some 

 fibrous materials tied up in bundles, such as 

 are still used by many savage peoples, and 

 were used in the old baronial halls. For 

 outdoor lights torches were used almost 

 down to our times, an indication of which is 

 seen in the iron torch-extinguishers at the 

 doors of many of the older West End 

 houses [of London] ; while, before the in- 

 troduction of gas, link-boys were as com- 

 mon in the streets as match-sellers are now. 

 Then came lamps, formed of small clay cups, 

 holding some melted animal fat and a 



fibrous wick; and, somewhat later, rush- 

 lights and candles; . . . but the three 

 modes of obtaining illumination for domes- 

 tic purposes remained entirely unchanged in 

 principle, and very little improved, through- 

 out the whole period of history down to the 

 end of the eighteenth century. WALLACE 

 The Wonderful Century, ch. 4, p. 27. (D. M. 

 & Co., 1899.) 



1930. LIGHT A SIGN OF UNITY 



Its Waves Pervade All Space. Nor is gravi- 

 tation the only agency which brings home 

 to us the unity of the conditions which pre- 

 vail among the worlds. There is another: 

 light that sweet and heavenly messenger 

 which comes to us from the depths of space, 

 telling us all we know of other worlds, and 

 giving us all that we enjoy of life and 

 beauty on our own. . . . Light is a 

 wave, or an undulatory vibration, and such 

 vibrations can only be propagated in a me- 

 dium which, however thin, must be material. 

 That this substance is at all like the chemi- 

 cal substance that we call " ether," is of 

 course a metaphor. It is a good metaphor 

 only in so far as the vapor of ether repre- 

 sents to us a form of matter which is very 

 thin, invisible, and impalpable. 

 Light, therefore, reveals to us the fact that 

 we are united with the most distant worlds, 

 and with all intervening space, by some 

 ethereal atmosphere, which embraces and 

 holds them all. ARGYLL Unity of Nature, 

 ch. 1, p. 6. (Burt.) 



1931. LIGHT AS KNOWN TO AN- 

 CIENTS Lens at Nineveh Combination of 

 Lenses Modern Telescope and Microscope. 

 About light the ancients knew more [than 

 about sound]. Their polished metal mir- 

 rors, flat and curved, had taught them the 

 first principles of reflection. Nor were they 

 ignorant of refraction; they already knew 

 the familiar experiment of putting a ring 

 in a basin and pouring in water till it be- 

 comes visible. A rock-crystal lens has been 

 dug up at Nineveh, and the Greeks and 

 Romans were well acquainted with glass 

 lenses. One is surprised that neither the 

 Arab astronomers, who knew a good deal of 

 optics, nor Roger Bacon, who in the thir- 

 teenth century gave an intelligent account of 

 their science, ever seem to have combined 

 two lenses into a telescope. It was not till 

 the seventeenth century that a telescope is 

 plainly mentioned in Holland, and Galileo, 

 hearing of it, made the famous instrument 

 with which he saw Jupiter's moons, and 

 revolutionized men's ideas of the universe. 

 The microscope and telescope may be called 

 inverted forms of one another, and their in- 

 ventions came nearly together. By these 

 two instruments the range of man's vision 

 has been so vastly extended beyond his un- 

 aided eyesight that animalcules under a 

 ten-thousandth of an inch long can now be 

 watched through all the stages of their life, 

 while stars whose distance from the earth is 

 hundreds of thousands of billions of miles 



