OBJECTS, PLEASURES, AND ADVANTAGES OF SCIENCE. six 



sucking-pump. Its weight is near fifteen pounds on every square inch, so that if we could entirely squeeze 

 out the air between our two hands, they would cling together with a force equal to the pressure of double 

 this weight, because the air would press upon both hands ; and if we could contrive to suck or squeeze out 

 the air between one hand and the wall, the hand would stick fast to the wall, being pressed on it with the 

 weight of above two hundredweight, that is, near fifteen pounds on every square inch of the hand. Now, bv 

 a most curious discovery made by Sir Everard Home, the distinguished anatomist, it is found that this is 

 the very process by which File* and other insects of a similar description are enabled to walk up 

 perpendicular surfaces, however smooth, as the sides of walls, and panes of glass in windows, and to walk as 

 easily along the ceiling of a room with their bodies downwards and their feet over head. Their feet, when 

 examined by a microscope, are found to have flat skins or flaps, like the feet of web-footed animals, as ducks 

 and geese ; and they have, by means of strong folds, the power of drawing the flap close down upon the 

 glass or wall the fly walks on, and thus squeezing out the air completely, so as to make a vacuum between 

 the foot and the glass or wall. The consequence of this is, that the air presses the foot on the wall with 

 a very considerable force compared to the weight of the fly ; for if its feet are to its body in the same propor- 

 tion as ours are to our bodies, since we could support by a single hand on the ceiling of the room (provided 

 it made a vacuum) more than our whole weight, namely, a weight of above fifteen stone, the fly can easily 

 move on four feet in the same manner by help of the vacuum made under its feet. 



It has likewise been found that some of the larger Sea-animah are, by the same construction, only upon 

 a greater scale, enabled to climb the perpendicular and smooth surfaces of the ice hills among which they 

 live. Some kiuds of Lizard have a like power of climbing, and of creeping with their bodies downwards 

 along the ceiling of a room ; and the means by which they are enabled to do so are the same. In the 

 large feet of those animal?, the contrivance is easily observed, of the toes and muscles, by which the skin 

 of the foot is pinned down, and the air excluded hi the act of walking or climbing; but it is the very same, 

 only upon a larger scale, with the mechanism of a fly's or a butterflv's foot; and both operations, the 

 climbing of the sea-horse on the ice, and the creeping of the fly on the window or the ceiling, are per- 

 formed eiactly by the same power, the weight of the atmosphere, which causes the quicksilver to stand in 

 the weather-glass, the wind to whistle through a key-hole, and the piston to descend in an old steam-engine. 



Although philosophers are not agreed as to the peculiar action which light exerts upon vegetation, and 

 there is even some doubt respecting the decomposition of air and water during that process, one thing 

 is undeniable, the necessity of light to the growth and health of plants: without it they have neither 

 colour, taste, nor smell ; and accordingly they are for the most part so formed as to receive it at all times 

 when it shines ou them. Their cups, and the little assemblages of their leaves before they sprout, are 

 found to be more or less affected by the light, BO as to open and receive it. In several kiqds of plants 

 this ia more evident than in others ; their flowers close entirely at night, and open in the day. Some 

 constantly turn round towards the light, following the sun, as it were, while he makes or seems to 

 make his revolution, BO that they receive the greatest quantity possible of his rays. Thus clover in a 

 field follows the apparent course of the sun. But all leaves of plants turn, to the sun, place them how you 

 will, light being essential to their thriving. 



The lightness of inflammable gas is well known. When bladders of any size are filled with it, they 

 ri.-e upwards, and float in the air. Now, taking advantage of this fact, Mr. Knight suggested that the fine 

 dust by means of which plants are impregnated one fro n another, is composed of very small globules, filled 

 with this gas in a word, of small air-balloons. These globules thus float from the male plant through the 

 air, and, striking against the females, are detained by a glue prepared ou purpose to stop them, which no 

 sooner moistens the globules than they explode, and their substance remains, the gas flying off which enabled 

 them to float. A provision of a very simple kind is also, in some cases, made to prevent the male and female 

 blossoms of the same plant from breeding together, this being found to hurt the breed of vegetables, just aa 

 breeding, in and in, spoils the race of animals. It is contrived that the dust shall be shed by the male 

 bloMom before the female of the same plant is ready to be affected by it ; BO that the impregnation must 

 be performed by the dust of some other plant, and in this way the breed be crossed. The light gas with 

 which the globules are filled is most essential to the operation, as it conveys them to great distances. A 

 plantation of yew-trees has been known, in this way, to impregnate another several hundred yards off. 



The contrivance by which some creeper plants are enabled to climb walls and fix themselves, deserves 

 attention. The Virginia creeper has a small tendril, ending in a claw, each toe of which has a knob, thickly 

 set with extremely small bristles ; they grow into the invisible pores of the wall, and swelling, stick there as 

 long as the plant grows, and prevent the branch from falling ; but when the plant dies, they become thin 

 gain, and drop out, so that the branch falls down. 



The Vanilla plant of the West Indies climbs round trees likewise by means of tendrils; but when it 

 has fixed itself, the tendrils drop off, and leaves are formed. 



It is found by chemical experiments, that the juice which is in the stomachs of animals (called the 

 yattric juice, from a Greek word signifying the belly) has very peculiar properties. Though it is for the most 

 part a tasteless, clear, and seemingly a very simple liquor, it nevertheless possesses extraordinary powers of 



