Imprint 

 Incandescence 



SCIENTIFIC SIDE-LIGHTS 



328 



and, if the shower be transient, these pits 

 retain their shape permanently, being dried 

 by the sun, and being then too firm to be 

 effaced by the action of the succeeding tide, 

 which deposits upon them a new layer of 

 mud. Hence we often find, in splitting open 

 a slab an inch or more thick, on the upper 

 surface of which the marks of recent rain 

 .occur, that an inferior layer, deposited dur- 

 ing some previous rise of the tide, exhibits 

 on its under side perfect casts of rain- 

 prints, which stand out in relief, the molds 

 of the same being seen on the layer ^below. 

 LYELL Principles of Geology, bk. ii, ch. 14, 

 p. 202. (A., 1854.) 



1602. IMPROVEMENT CEASES 

 WITH LACK OF COMPETITION The 



Humming-bird Has No Rival in Its Own 

 Field. It is perhaps a law of Nature that 

 when a species (or group) fits itself to a 

 place not previously occupied, and in which 

 it is subject to no opposition from beings 

 of its own class, or where it attains so great 

 a perfection as to be able easily to overcome 

 all opposition, the character eventually 

 loses its original plasticity, or tendency to 

 vary, since improvement in such a case 

 would be superfluous, and becomes, so to 

 speak, crystallized in that form which con- 

 tinues thereafter unaltered. It is, at any 

 rate, clear that while all other birds rub 

 together in the struggle for existence, the 

 humming-bird, owing to its aerial life and 

 peculiar manner of seeking its food, is abso- 

 lutely untouched by this kind of warfare, 

 and is accordingly as far removed from all 

 competition with other birds as the solitary 

 savage is removed from the struggle of life 

 affecting and modifying men in crowded 

 communities. The lower kind of competi- 

 tion affecting humming-birds, that with in- 

 sects, and, within the family, of species with 

 species, has probably only served to inten- 

 sify their unique characteristics, and, per- 

 haps, to lower their intelligence. HUDSON 

 Naturalist in La Plata, ch. 16, p. 217. (C. 

 & H., 1895.) 



1603. IMPULSE FOR HABITUAL 

 MOVEMENT SUPPLIED BY LAST PRE- 

 CEDING MOVEMENT In action grown 

 habitual, what instigates each new muscular 

 contraction to take place in its appointed 

 order is not a thought or a perception, but 

 the sensation occasioned by the muscular 

 contraction just finished. A strictly volun- 

 tary act has to be guided by idea, percep- 

 tion, and volition, throughout its whole 

 course. In an habitual action, mere sensa- 

 tion is a sufficient guide, and the upper re- 

 gions of the brain and mind are set com- 

 paratively free. JAMES Psychology, vol. i, 

 ch. 4, p. 115. (H. H. & Co., 1899.) 



1604. IMPULSE, MIGRATORY, IN 

 CAGE-BIRDS Desertion of Young by Mother- 

 birds An Instinct Stronger than Maternal 

 Affection. Nearly every bird is, indeed, 

 more or less migratory; that is, it changes 

 its quarter to a certain extent according to 



the season of the year. Even cage-birds, 

 reared from the eggs of parents who never 

 knew what freedom was, get as uneasy as a 

 Londoner in August, and if their prison- 

 doors are left open will sometimes desert 

 their helpless young in order not to be too 

 late for the winter hegira. The house- 

 martin has been known to do so repeatedly; 

 and if the autumn is colder than usual, the 

 swallow and the Carolina waxwing will 

 suddenly take their departure from Canada, 

 leaving their callow brood to die of starva- 

 tion, the instinct of self-preservation being 

 evidently stronger than that of maternal af- 

 fection. BROWN Nature-Studies, p. 14. 

 (Hum., 1888.) 



1605. IMPULSE TO ACQUISITION 

 Loss Involves Seeming Shrinkage of Our- 

 selves. An . . . instinctive impulse 

 drives us to collect property; and the collec- 

 tions thus made become, with different de- 

 grees of intimacy, parts of our empirical 

 selves. The parts of our wealth most inti- 

 mately ours are those which are saturated 

 with our labor. There are few men who 

 would not feel personally annihilated if a 

 lifelong construction of their hands or 

 brains say an entomological collection or 

 an extensive work in manuscript were sud- 

 denly swept away. The miser feels simi- 

 larly towards his gold, and altho it is true 

 that a part of our depression at the loss of 

 possessions is due to our feeling that we 

 must now go without certain goods that we 

 expected the possessions to bring in their 

 train, yet iri every case there remains, over 

 and above this, a sense of the shrinkage of 

 our personality, a partial conversion of our- 

 selves to nothingness, which is a psycho- 

 logical phenomenon by itself. We are all at 

 once assimilated to the tramps and poor 

 devils whom we so despise, and at the same 

 time remove farther than ever away from 

 the happy sons of earth who lord it over 

 land and sea and men in the full-blown 

 lustihood that wealth and power can give, 

 and before whom, stiffen ourselves as we 

 will by appealing to anti-snobbish first 

 principles, we cannot escape an emotion, 

 open or sneaking, of respect and dread. 

 JAMES Psychology, vol. i, ch. 10, p. 293. (H. 

 H. & Co., 1899.) 



1606. IMPULSES RIPEN SUCCES- 

 SIVELY The Flowering-time an Opportunity 

 To Be Seised. In children we observe a 

 ripening of impulses and interests in a cer- 

 tain determinate order. Creeping, walking, 

 climbing, imitating vocal sounds, construct- 

 ing, drawing, calculating, possess the child 

 in succession; and in some children the 

 possession, while it lasts, may be of a semi- 

 frantic and exclusive sort. Later, the inter- 

 est in any one of these things may wholly 

 fade away. Of course, the proper pedagogic 

 moment to work skill in, and to clench the 

 useful habit, is when the native impulse is 

 most acutely present. Crowd on the ath- 

 letic opportunities, the mental arithmetic, 

 the verse-learning, the drawing, the botany, 



