2 74 



SCIENTIFIC NE^A^S. 



[Mar. 23, iS 



trates the downward pressure of water. The flask can 

 never be filled any deeper. Any excess of water 

 introduced escapes until that level is reached. The flask 

 may now be emptied, and a cork fitted with two small tube 

 of any size and shape is inserted from above into the neck. 

 Water is now poured into these. The object of having two 

 tubes is to permit air to escape from the space between 

 the cork and plate. A single tube, if of sufficient diameter, 

 will answer. As soon as the marked level is reached 

 the plate is again forced off its seat and water escapes. 

 The tubes can only be filled to the same level as the large 

 vase. Finally, the tubes are removed, the flask is half- 

 filled, and a solid cylinder, such as an empty bottle, is 

 immersed in the water so as to raise its level. Nothing 

 happens until the mark is reached, when again the plate 

 is forced off' its seat and water escapes. 



Thus the law is proved that the pressure exerted by a 

 column of water on a given area varies with the height 

 of the columnof fluid producing it, and not with its volume 

 or shape. — Scientific America?!. 



■•~>>^l^i^-* 



THE STRUGGLE FOR LIFE IN THE 

 SEA AND IN FRESH WATERS. 



CHANGE in the animal life of the sea is more exten- 

 sive and rapid than in fresh waters. A very little 

 reflection will convince those who have some acquaint- 

 ance with the history of life on the earth that this is ac- 

 tually so. We have only to go back as far as the chalk 

 period to find the animal life of the sea entirely different 

 from its present population, and in still earlier times the 

 changes were so frequent and so complete as to give 

 colour to the ancient doctrine, now abandoned, that all 

 the life of the earth had been swept away at intervals by 

 universal outbreaks of destructive energy. That doc- 

 trine is at once refuted by the many cases of freshwater 

 animals which have survived with little change several 

 of the supposed world-wide catastrophes. In freshwater 

 deposits older than the chalk (Wealden and Purbeck) we 

 find some of our familiar pond-snails and pond-mussels, 

 while in the inconceivably remote time of the Coal 

 Measures, and even earlier, our pond-mussel had a near 

 representative. 



This absence of rapid change in the life of freshwaters 

 depends upon comparative exemption from competition. 

 Races which have proved too feeble, too old-fashioned, 

 one might say, to resist the tide of experiment and inno- 

 vation in the broad seas, manage to struggle on in the 

 contracted and scattered freshwater basins of the world. 

 Thus it comes about that such antique forms as the 

 Ganoid fishes survive in fresh waters, and there only. 

 In their palmy days they could hold their own in the 

 waters of the sea. Now they survive only in fresh 

 waters, and there by virtue of isolation. 



There is, as it were, a difference of pressure between 

 the full tide of life in the open sea, and the sluggish per- 

 sistence of animals confined to land-locked waters. This 

 is illustrated by the many cases of marine animals which 

 have become fluviatile. The perch is a familiar case 

 among fishes, and Dr. Giinther speaks decidedly as to the 

 frequent occurrence of such transitions. Within human 

 recollection a brackish vv^ater bivalve {Dreissena) and a 

 marine or brackish water polyp (Cordylophora) have 

 made themselves at home in our freshwater canals. 



The explanation of all the facts cited is to be fojand in 



the relative extent and continuity of the two spheres. It 

 is the difference between a wide continent and a lonely 

 island. In the ocean, as on the continent, competition 

 and innovation are rife ; in the island or river-basin un- 

 changed persistence is favoured by the fewness of com- 

 peting forms and the rare appearance of new and 

 destructive races. The wide sea or continent is, to 

 borrow an illustration from human experience, the busy 

 world of commerce, and invention, and restless thought, 

 while the land-locked pool or oceanic island resembles a 

 remote country village, where two hundred years have 

 brought no conspicuous change in dwellings or food or 

 dress. What the introduction of a railway is to the vil- 

 lage, the breaking down of natural barriers may be to 

 the population of the island and (more rarely) even to 

 that of the river-basin. The hardy product of the wide 

 and busy area encroaches upon the long-secluded popu- 

 lation, and compels rapid changes, even if it does not 

 bring sudden destruction. 



The same difference in the physical conditions is ac- 

 countable for the singular fact that metamorphosis, or 

 development with transformation, is so common in the 

 animals of the sea, and so rare in those of the narrower 

 lakes and rivers. Where the struggle for existence is 

 keen, and the water is filled with strong and cunning 

 creatures eager to prey upon weaker rivals, vast num- 

 bers of eggs are produced to compensate for the vast 

 destruction. They are turned out very early, and, as it 

 were, " sent before their time, into this breathing world, 

 scarce half made up." Accordingly, they differ con- 

 spicuously from their parents, or from the adult state of 

 the few which gain full size. In the calmer waters of 

 the lake and river few eggs are produced, and these are 

 larger, better cared for, and take longer to develop ; so 

 that the form which issues often completely resembles 

 the parent, except in size. The fluviatile frog, which will 

 occur to some readers as an exception, is only appar- 

 ently so. The tadpole actually represents the adult 

 normal condition of its class, and the change to the leap- 

 ing, land-traversing frog, belongs not to embryonic 

 development, but to the same kind of aduU transforma- 

 tion as the assumption of horns by the stag, or a beard 

 by man. 



We can thus rationally connect differences in liability 

 to change, in invading power, and in the presence or 

 absence of transformation. All will be found to depend 

 upon the extent of the area inhabited, and the freedom 

 of communication within it. It may be considered fair 

 proof of the validity of the explanation that it applies, not 

 only to the sea and the small freshwater basin, but 

 equally well to the case (so unlike at first sight) of the 

 continent and oceanic island, where the sole point of 

 analogy is that contrast of size which we have found to 

 be so influential. 



Restoring Linens. — The washerwomen of Holland and 

 Belgium, so proverbially clean, who get up their linen so 

 beautifully white, use refined borax as a washing powder, 

 instead of soda, in the proportion of a large handful of borax 

 powder to about ten gallons of boiling water. They save in 

 soap neariy one-half. All the large washing establishments 

 adopt the same mode. For laces, cambrics, etc., an extra 

 quantity of the powder is used, and for crinolines (required 

 to be very stiff) a strong solution is necessary. Borax being 

 a neutral salt, does not in the slightest degree injure the 

 texture of the linen ; its effect is to soften the hardest water. 

 The laundries of Holland are said to turn out beautiful 

 work. 



