157 



SCIENTIFIC SIDE-LIGHTS 



Klta 

 nial 



ing this idea of the smallness of the sea, to 

 which the misunderstood expression of " the 

 ocean stream " contributed not a little. 

 HUMBOLDT Cosmos, vol. i, pp. 288-9. (H., 



765. DELUSIONS DUE TO NATURAL 



CAUSES Cause of Mirage Reflection from a 

 Surface of Heated Air. Total reflection 

 never occurs except in the attempted passage 

 of a ray from a more refracting to a less re- 

 fracting medium ; but in this case, when the 

 obliquity is sufficient, it always occurs. The 

 mirage of the desert, and other phantasmal 

 appearances in the atmosphere, are in part 

 due to it. When, for example, the sun heats 

 an expanse of sand, the layer of air in con- 

 tact with the sand becomes lighter and less 

 refracting than the air above it; conse- 

 quently, the rays from a distant object, 

 striking very obliquely on the surface of the 

 heated stratum, are sometimes totally re- 

 flected upwards, thus producing images simi- 

 lar to those produced by water. I have seen 

 the image of a rock called Mont Tombeline 

 distinctly reflected from the heated air of 

 the strand of Normandy near Avranches; 

 and by such delusive appearances the thirsty 

 soldiers of the French army in Egypt were 

 greatly tantalized. TYNDALL Lectures on 

 Light, lect. 1, p. 19. (A., 1898.) 



766. DEMOCRACY AND ARISTOC- 

 RACY AS AFFECTING SCHOLARLY PUR- 

 SUITS Social Permanence Favors Study of 

 Pure Science. In a work published in 1850, 

 De Tocqueville says : " It must be confessed 

 that, among the civilized peoples of our age, 

 there are few in which the highest sciences 

 have made so little progress as in the United 

 States." He declares his conviction that, 

 had you been alone in the universe, you 

 would soon have discovered that you cannot 

 long make progress in practical science 

 without cultivating theoretic science at the 

 same time. But, according to De Tocque- 

 ville, you are not thus alone. He refuses to 

 separate America from its ancestral home; 

 and it is there, he contends, that you collect 

 the treasures of the intellect without ta- 

 king the trouble to create them. De Tocque- 

 ville evidently doubts the capacity of a 

 democracy to foster genius as it was fostered 

 in the ancient aristocracies. " The future," 

 he says, " will prove whether the passion for 

 profound knowledge, so rare and so fruitful, 

 can be born and developed so readily in 

 democratic societies as in aristocracies. As 

 for me," he continues, " I can hardly believe 

 it." He speaks of the unquiet feverishness 

 of democratic communities, not in times of 

 great excitement, for such times may give 

 an extraordinary impetus to ideas, but in 

 times of peace. There is then, he says, " a 

 small and uncomfortable agitation, a sort 

 of incessant attrition of man against man, 

 which troubles and distracts the mind with- 

 out imparting to it either loftiness or ani- 

 mation." TYNDALL Lectures on Light, p. 

 225. (A., 1898.) 



767. DEMONSTRATION DEFINED 



Circumstantial Evidence May Have Equal 

 Force. What we call " demonstration " 

 rests entirely upon our mental inability to 

 accept as true anything that contravenes 

 the thing affirmed; and if, in a chain of 

 demonstrative reasoning, every link has the 

 strength of a necessary truth, we accept its 

 conclusion as having the same validity as 

 the datum from which it started. Now, I 

 hold that exactly the same state of " convic- 

 tion " may be produced by a Concurrence of 

 probabilities, if these point separately and 

 independently to the same conclusion like 

 radial lines that converge from different 

 parts of the circumference of a circle, tho 

 none actually reach its center. For the re- 

 sult of that concurrence may be as irresist- 

 ibly probative as any demonstration; the 

 conclusion to which they all point being one 

 which we are compelled to accept by our in- 

 ability to conceive of any other explanation 

 of the whole aggregate of evidentiary facts, 

 tho any one of them may be otherwise ac- 

 counted for. I am not aware that this prin- 

 ciple has been discussed in any treatise on 

 logic; but it is familiar to every lawyer 

 who practises in courts of justice, and its 

 validity cannot, I think, be questioned by 

 any one who has studied the theory of what 

 is commonly called " circumstantial " evi- 

 dence. Indeed, it would be difficult to ad- 

 duce a more remarkable example of the 

 stability of an argument erected on a broad 

 basis of independent probabilities than is 

 presented in the wonderful fabric built up 

 by the genius of Darwin; the general ac- 

 ceptance of the evolution doctrine resting on 

 exactly the same kind of evidence as that on 

 which I base the argument from design. 

 CARPENTER Nature and Man, lect. 15, p. 415. 

 (A., 1889.) 



768. DENIAL OF THEOLOGY NOT 

 ABANDONMENT OF RELIGION Religious 

 Habit of Mind as a Survival. Sects or in- 

 dividuals, who have come to reject all defi- 

 nite theological conceptions and to deny the 

 existence of a living God,"have, nevertheless, 

 been able to retain feelings and sentiments 

 which may justly claim to be called relig- 

 ious. In the first place, with many men of 

 this kind, their denial of a God is not in 

 reality a complete denial. What they deny 

 is very often only some particular concep- 

 tion of the Godhead, which is involved, or 

 which they think is involved, in the popular 

 theology. They are repelled, perhaps, by the 

 familiarity with which the least elevated of 

 human passions are sometimes attributed to 

 the Divine Being. Or they may be puzzled 

 by the anomalies of Nature, and find it im- 

 possible to reconcile them intellectually with 

 any definite conception of a Being who is 

 both all-powerful and all-good. But in fal- 

 tering under this difficulty, or under other 

 difficulties of the same kind, and denying the 

 possibility of forming any clear or definite 

 conceptions of the Godhead, they do not nec- 

 essarily renounce other conceptions which, 



