Polarization 

 Poverty 



SCIENTIFIC SIDE-LIGHTS 



536 



2643. POLARIZATION OF LIGHT 



Tourmalin Quenches All but One Set of 

 Vibrations Two Crossed Plates Produce 

 Darkness. We may begin the study of the 

 polarization of light, with ease and profit, 

 by means of a crystal of tourmalin. But 

 we must start with a clear conception of an 

 ordinary beam of light. It has been al- 

 ready explained that the vibrations of 

 the individual ether-particles are executed 

 across the line of propagation. In the case 

 of ordinary light we are to figure the ether- 

 particles as vibrating in all directions, or 

 azimuths, as it is sometimes expressed, 

 across this line. Now, in the case of a plate 

 of tourmalin cut parallel to the axis of the 

 crystal, a beam of light incident upon the 

 plate is divided into two, the one vibrating 

 parallel to the axis of the crystal, the other 

 at right angles to the axis. The grouping 

 of the molecules and of the ether associated 

 with the molecules reduces all the vibra- 

 tions incident upon the crystal to these two 

 directions. One of these beams, namely, 

 that whose vibrations are perpendicular to 

 the axis, is quenched with exceeding rapid- 

 ity by the tourmalin. To such vibrations 

 many specimens of the crystal are highly 

 opaque, so that, after having passed through 

 a very small thickness of the tourmalin, 

 the light emerges with all its vibrations 

 reduced to a single plane. In this condition 

 it is what we call plane polarised light. 

 A moment's reflection will show that, if 

 what is here stated be correct, on placing 

 a second plate of tourmalin with its axis 

 parallel to the first, the light will pass 

 through both; but that, if the axes be 

 crossed, the light that passes through the 

 one plate will be quenched by the other, 

 a total interception of the light being the 

 consequence. TYNDALL Lectures on Light, 

 lect. 3, p. 115. (A., 1898.) 



2644. POLITICS AN EDUCATION 



Increasing Knowledge of Social Laws Pro- 

 vision against Pauperism. The very at- 

 tempt of the working classes to govern 

 through combination their own affairs, and 

 to determine their own condition, is an edu- 

 cation in itself. On the extended scale on 

 which that attempt is being made it must 

 accustom them to consider great general 

 causes, and to estimate the manner and 

 the degree in which these can be effected 

 by the methods of adjustment. Last, not 

 least, it must lead them to study and to 

 recognize the moral duties which are indeed 

 the most fundamental of all natural laws. 

 For it ought to be remembered that the first 

 and most important object of combinations 

 is one against which there can be no oppo- 

 sition founded on the doctrines of economic 

 science. That object is to secure for the 

 working classes those provisions against 

 misfortune, sickness, accident, and age which 

 are amongst the first duties of all organized 

 societies of men. How far through such 

 agency the causes of pauperism may be suc- 



cessfully attacked is a question on which 

 we are only entering. In like manner, the 

 conditions and limitations under which com- 

 bination may succeed in blending the func- 

 tions and in uniting the profits of capital 

 and of labor this also is a question to be 

 determined by natural laws, not yet fully 

 explored or understood. ARGYLL Reign of 

 Law, ch. 7, p. 226. (Burt.) 



2645. POLLUTION AT THE SOURCE 



Foul Springs and Wells Spread Disease. 

 Gathering-grounds are frequently the lo- 

 cality of the pollution. The recent Maid- 

 stone epidemic is an example. Here some 

 of the springs supplying the town with wa- 

 ter were contaminated by se\eral typhoid 

 patients. Frequently on the gathering- 

 ground one may find a number of houses 

 the waste and refuse of which will furnish 

 ample surface pollution, which in its turn 

 may readily pass into a collecting reservoir 

 or a well. Only recently the writer inves- 

 tigated the cause of typhoid in a large coun- 

 try house, and traced it to pollution of the 

 private well by surface washings from the 

 stable quarters. Leakage of house-drains 

 into wells is not an infrequent source of 

 contamination. NEWMAN Bacteria, ch. 2, p. 

 82. (G. P. P., 1899.) 



2646. POLYGAMY NOT PRIMEVAL- 



General Equality of the Sexes. We have 

 seen that the cruel treatment of the female 

 sex is almost universal among savages, and 

 that it is entirely unknown among the lower 

 animals. It is in the highest degree im- 

 probable and unnatural to suppose that this 

 habit can have been primeval. But the 

 same considerations carry us a great deal 

 farther. They raise a presumption in favor 

 of the later origin of other habits and cus- 

 toms which are not confined to the savage 

 state, but have prevailed and do now prevail 

 among nations comparatively civilized [such 

 as polygamy and marriage by capture.] 

 There can have been no polygamy when 

 as yet there was only a single pair, or when 

 there were several single pairs widely sepa- 

 rated from each other. The presumption, if 

 not the certainty, therefore, is that primeval 

 man must have been monogamous. It is a 

 presumption supported by the general equal- 

 ity of the sexes in respect to the num- 

 bers born, with only just such an excess of 

 the male sex as tends to maintain that 

 equality against the greater risks to life 

 arising out of manly pursuits and duties. 

 Thus the facts of Nature point to polygamy 

 as in all probability a departure from the 

 habits of primeval times. ARGYLL Unity 

 of Nature, ch. 10, p. 229. (Burt.) 



2647. POTTER'S WHEEL KNOWN 

 FROM EARLY ANTIQUITY All power at 

 first was hand power; the machinery of 

 the world was moved only by human mus- 

 cles. . . . Winds and water currents 

 gradually have been domesticated for human 

 uses in savagery. The study of these is 



