Crystals 

 Cycle 



SCIENTIFIC SIDE-LIGHTS 



144 



of their polar forces. They arrange them- 

 selves in obedience to these forces, a minute 

 crystal of niter being at first produced. On 

 this crystal the molecules continue to de- 

 posit themselves from the surrounding 

 liquid. The crystal grows, and finally we 

 have large prisms of niter, each of a per- 

 fectly definite shape. Alum crystallizes 

 with the utmost ease in this fashion. The 

 resultant crystal is, however, different in 

 shape from that of niter, because the poles 

 ef the molecules are differently disposed. 

 If they be only nursed with proper care, 

 crystals of these substances may be caused 

 to grow to a great size. TYNDALL Lectures 

 on Light, lect. 3, p. 102. (A., 1898.) 



709. CURIOSITY A TRAIT OF 



SEALS Music and Church Bells Attract Them. 

 [The common seal], like other species of 

 the group, is certainly attracted by musical 

 sounds; probably only through curiosity, 

 because it is similarly attracted by any un- 

 usual movements. Mr. Bell tells us, in his 

 " British Quadrupeds," that, in the Orkney 

 Islands, if people are passing in boats, seals 

 will often come quite close up to the boat, 

 and stare at them, following for a long time 

 together; if people speak loud, they seem to 

 wonder what may be the matter! The 

 Church of Hoy, in Orkney, is situated near 

 a small sandy bay, much frequented by these 

 creatures, and it was observed that when 

 the bell rang for divine service all the seals 

 within hearing swam directly for the shore, 

 and kept looking about them, as if surprised 

 rather than frightened, and this continued 

 as long as the bells rang. MIVART Types of 

 Animal Life, ch. 10, p. 289. (L. B. & Co., 

 1893.) 



710. CURIOSITY OF MONKEYS 

 Mr. Darwin, who, in order to test the state- 

 ment of Brehm that monkeys have an in- 

 stinctive dread of snakes, and yet cannot 

 " desist from occasionally satiating their 

 curiosity in a most human fashion, by lift- 

 ing up the lid of the box in which the snakes 

 were kept," took a stuffed snake to the 

 monkey-house at the Zoological Gardens. 

 Mr. Darwin says : " The excitement thus 

 caused was one of the most curious spec- 

 tacles I ever beheld. ... I then placed 

 a live snake in a paper bag, with the mouth 

 loosely closed, in one of the larger compart- 

 ments. One of the monkeys immediately ap- 

 proached, cautiously opened the bag, peeped 

 in, and instantly dashed away. Then I wit- 

 nessed what Brehm has described, for mon- 

 key after monkey, with head raised high and 

 turned on one side, could not resist taking 

 a momentary peep into the upright bag, at 

 the dreadful object lying quietly at the bot- 

 tom." ROMANES Animal Intelligence, ch. 

 17, p. 477. (A., 1899.) 



711. CURRENT OF ELECTRICITY 

 NON-EXISTENT A Figure of Speech Elec- 

 tric Action by Atomic Motion The Row of 

 Bricks. Having established the so-called 



electric current, we will now try to show you 

 that there really is no current. The idea 

 of a current involves the idea of a fluid sub- 

 stance flowing from one point to another. 

 When you were a boy did you never set up a 

 row of bricks on their ends, just far enough 

 apart so that if you pushed one over they 

 all fell one after another? Now, imagine 

 rows of molecules or atoms, and in your 

 imagination they may be arranged like the 

 bricks, so that they are affected one by the 

 other successively with a rapidity that is 

 akin to that of light-waves, and you can con- 

 ceive how a motion may be communicated 

 from end to end of a wire hundreds of miles 

 in length in a small fraction of a second, and 

 no material substance has been carried 

 through the wire only energy. We do not 

 mean to say that the row of bricks illus- 

 trates the exact mode of molecular or atomic 

 motion that takes place in a conductor. 

 What we mean is, that in some way motion 

 is passed along from atom to atom. ELISHA 

 GRAY Nature's Miracles, vol. iii, ch. 6, p. 53. 

 (F. H. &H., 1900.) 



712. CURRENTS AS A MEANS OF 

 DISTRIBUTION OF ANIMAL ORGANISMS 



By far the greater number of invertebrate 

 animals freely swimming or floating in wa- 

 ter are incapable of offering any resistance 

 to the current, and are therefore carried 

 along in the direction which the current it- 

 self takes. All the larvae of sponges, polyps, 

 annelida, tunicata, echinodermata, and very 

 many mollusca, . . . and the medusae, 

 tho many of these are provided with special 

 swimming "organs, are perfectly incapable of 

 swimming against the feeblest stream. The 

 only invertebrate animals which are able to 

 overcome perhaps the strongest currents are 

 the cuttlefishes. 



The well-known wealth of forms in the 

 Mediterranean and in the Red Sea owes its 

 origin, certainly in great part, to the action 

 of the constant marine currents. Both these 

 seas are connected with the ocean only by 

 narrow straits through which a superficial 

 current incessantly flows in. The strength of 

 these currents may vary with the time of 

 year and the direction of the prevailing 

 winds, but their direction is invariable the 

 whole year through. Hence all the animals 

 drifting on or just below the surface, when 

 once they nave been carried in through these 

 narrow straits, cannot easily get back to the 

 open ocean, and so all the forms that never 

 sink below a certain inconsiderable depth 

 must remain in the inland sea, and only 

 those few species or individuals which reach 

 the deeper return current and do not leave it 

 can be in a position to be borne back by it to 

 the ocean. Consequently both these seas, by 

 reason of the inflowing surface currents, are 

 a sort of trap; everything can get in, but 

 nothing can get out again; thus it is in- 

 evitable and it is actually the case that a 

 vast accumulation of species as well as of 

 individuals occurs in these seas, wherever 



