460 



SCiENtlFIC NE^ArS. 



[May 18, 1888. 



to the framework of the turret, the teeth of which 

 remain in contact during the vertical movement. 



To cause the turret to descend, the inventor makes use 

 of a system of levers / / /, and they are arranged in such 

 a manner that the speed either of ascent or descent in- 

 creases from the starting point to the middle of its course, 

 and then decreases progressively to the point of arrival. 



The water in which the plunger is immersed cannot 

 well be frozen, but if necessary it is easy to form a mix- 

 ture which will not freeze at the lowest temperature to 

 which it will be exposed. 



The armament is composed of two pieces mounted, on 

 carriages fitted with hydraulic brakes and means of re- 

 turning automatically in position. Each cannon with 

 its supports is counterpoised by a plunger arranged 

 similarly to that of the turret. A single person can 

 manoeuvre the piece. 



*-^t^>^i^-f 



SOIL AND SOIL MAKERS. 



WHAT is soil ? To most people merely the upper 

 layer which, in general,is found covering the dry 

 land, and which differs very considerably, both in its tex- 

 ture and its composition, according to the nature of thfe 

 underlying strata, the climate, and the supply of moisture. 

 But let us in imagination take an excursion ticket to some 

 heavenly body, cooled down sufficiently to permit of the 

 existence of life, but on which no life has, as yet, come 

 into existence. Let us take our walks abroad and examine 

 the ground beneath our feet. We shall see, and can see, 

 there no soil such as we commonly meet with in this 

 world, whether in its cultivated or its desert parts. We 

 shall certainly find a layer ofmineral matter, more or less 

 finely broken up by the alternate action of sun and frost, 

 by the contact of the carbonic acid in the air and that of 

 atmospheric moisture. But it will be less thoroughly 

 disintegrated and mixed together than the soils which we 

 meet with. It will contain no residues of organic matter, 

 the result of animal and vegetable life. As a consequence 

 its power of absorbing gases and vapours from the air, and 

 of retaining water, will be very much less than that of a 

 true soil, containing from 2 to perhaps 8 to 10 per cent, 

 of organic remains. 



Hence, we learn, incidentally, that life can only be 

 introduced into a world very gradually, beginning with 

 very humble forms. Plants and trees, generally speaking, 

 cannot grow without soil ; animals, without exception, 

 are nourished, directly or indirectly, from plants, so that, 

 as regards the organic world, we seem to be pent up in a 

 vicious circle : soil cannot be formed without organic life, 

 and organic life presupposes soil. There is, however, a 

 way of escape. The spores of certain lichens can vege- 

 tate upon a bare rock. They condense from the air gases 

 which form the bulk of their tissues. Among their pro- 

 ducts thus obtained is oxalic acid, which gradually de 

 composes the rock, extracting from it those earths and 

 alkalies which plants require as part of their structures. 

 As centuries roll on, and generation after generation of 

 these lowly organisms perishes, each bequeaths to its 

 successors the lime, the potash, the compounds of carbon 

 and hydrogen which it has gleaned from the rocks and 

 the atmosphere ; and thus gradually, very gradually, soil 

 is formed. Higher members of the plant world and 

 animals now by degrees put in an appearance, and the 

 process of soil-making goes on at an accelerated rate. It 

 will be remembered that with the origin of animal and 

 vegetable species we have here nothing to do. Whether 

 they are evolved in succession or directly successively 



created, the result is the same. We are here merely 

 studying the part they take in the formation of soils. 



Among the soil-makers an important, though invisible, 

 part is played by those minute plants known collectively 

 as microphytes. Without their aid the remains of plants 

 and animals, unless devoured by some refuse-eating 

 species, would simply encumber the ground, instead of 

 being utilised for the nourishment of plants, and thus, 

 indirectly, for the food of animals. These same micro- 

 scopic beings also seize upon the nitrogen of dead organic 

 matter, and convert it into ammonia or, according to cir- 

 cumstances, into nitric acid. Such nitric acid, like the 

 oxalic acid elaborated by certain plants, assists in decom- 

 posing phosphatic minerals, rendering their phosphoric 

 acid availalale as plant-food. Indeed, we are only 

 beginning to comprehend the chemical changes which these 

 ultra-microscopic beings effect both in soils and waters. 



But in the great process of soil-making other and more 

 powerful agents are also required. It is necessary to 

 bring the lower portions of the soil up to the surface, and 

 expose them, in a fine state of division, to the action of 

 the atmosphere, of rain and dew, of sunshine and frost. 

 It is no less necessary to carry down dead animals, leaves, 

 stalks, and, in short, refuse generally, into the lower 

 parts of the soil, so that the gases and vapours which they 

 give oft" may be absorbed, whilst the residual solid par- 

 ticles are well mixed up with the mineral or non-organic 

 portion of the soil. 



This double task is executed by a number of animals 

 belonging to very different classes. Foremost stand, 

 perhaps, the earth-worms — if not from the predominating 

 extent and value of their labours, yet from the admirable 

 manner in which their economy has been studied by 

 Charles Darwin. They draw down into their holes all 

 small fragments of decomposing matter, vegetable and 

 probably animal, which they find about. Not only so, 

 they literally eat the soil, voiding it afterwards in a state 

 of very fine subdivision. At the same time their holes 

 admit air and moisture into the soil, and thus aid power- 

 fully in bringing it into fine condition for the growth of 

 plants. But we feel the less disposed to enlarge on their 

 manner of working, and on its results, since we trust that 

 most of our readers will have met with Darwin's work. 

 Many species of insects take a share in the same task. 

 The so-called carrion and dung-beetles {Geolnipes, Aplio- 

 dius, Necrophorus, etc.) dig shafts into the earth, neces- 

 sarily bringing up a quantity of soil to the surface, and 

 convey down small dead animals, excrementitious 

 matter, etc., thus at once fertilising the lower regions of 

 the soil, and preventing nuisance. 



The so-called "white ants" (Termes), so numerous in 

 most tropical and sub-tropical countries, are also diligent 

 soil-makers. With clay and sand, which they fetch up 

 from below the surface, they construct not merely their 

 cities, but covert-ways leading to quarters where they 

 plunder. As these structures gradually crumble away 

 and are scattered in the form of fine dust, hundreds of 

 thousands of tons of clay are thus yearly comminuted, 

 mixed up with other matters, and converted into arable 

 soil in a far more perfect manner than it could be done 

 by plough, harrow, or spade. Very similar work, and 

 over a wider area, from north to south is effected by the 

 true ants. Professor Shaler finds that in certain sandy 

 soils the overturnings effected by these little creatures 

 become of geological importance. He observes that in 

 certain sandy soils the glacial terraces and plains are 

 covered to the depth of a foot or more with fine sand 



