32 OBJECTS, ADVANTAGES, AND 



it were very thick ; a round one, having the strength of an arch, would 

 resist better ; but any soft substance, as leather or skin, would be crushed 

 or squeezed together at once. If the air was only sucked out slowly, 

 the squeezing would be gradual, or, if it were only half sucked out, the 

 skin would only be partly squeezed together. This is the very process 

 by which Bees reach the fine dust and juices of hollow flowers, like the 

 honeysuckle, and some kinds of long fox-glove, which are too narrow 

 for them to enter. They fill up the mouth of the flower with their bodies, 

 and suck out the air, or at least a large part of it ; this makes the soft 

 sides of the flower close, and squeezes the dust and juice towards the 

 insect as well as a hand could do, if applied to the outside. 



We may remember this pressure or weight of the atmosphere as 

 shown by the barometer, the sucking-pump, and the air-pump. Its 

 weight is near 15 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 hundred weight, that is, near 15 pounds on every square 

 inch of the hand. Now, by a late most curious discovery of Sir 

 Everard Home, the distinguished anatomist, it is found that this is the 

 very process by which Flies 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 towards the back part or heel, but inside 

 the skin or flap, two very small toes so connected with the flap as to 

 draw it close down upon the glass or wall the fly walks on, and 

 to squeeze out the air completely, so that there is a vacuum made 

 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 proportion 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 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 animals 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 kinds of lizard have the same 

 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 da 

 so are the same. In the large feet of these animals, the contrivance is 

 easily observed, of the two toes or tightners, by which the skin of the 

 foot is pinned down, and the air excluded in 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 butterfly's foot ; and both operations, the 

 climbing of the sea-horse on the ice, and the creeping of the fly on the* 



