Now, the apparent diameters of the sun and earth, at their mean distance, are 1922″, 8, and 17″, 1552, and the mass of the earth is the 354,936th part of that of the sun, taken as the unit. It follows, therefore, that the earth is nearly four times as dense as the sun; but the sun is so large that his attractive force would cause bodies to fall through about 335 feet in 1″; consequently, if inhabited by human beings, they would be unable to move, since their weight would be thirty times as great as it is here." A man of moderate size would weigh about two tons at the surface of the sun; whereas, at the surface of the asteroids, (the clusters between Mars and Jupiter,) he would be so light that he could not stand steadily, since he would only weigh a few pounds. The densities, that of water being 1, as far as can be satisfactorily explained, are as follow:--Sun, 1-2/15; Mercury, 9-1/6; Venus, 5-11/15; Moon, 4-1/2; Mars, 3-2/7; Ceres, 2; Pallas, 2; Jupiter, 1-1/24; Saturn, 13/32; Herschel, 99/100. Similar observations apply to the influence of the atmosphere, in whatever point of view we consider it, that is, whether we regard its weight, its electrical condition, its illumination, its temperature, its dryness, or humidity. 1. _Its Weight._--The weight of the atmosphere (an elastic, compressible, and expansible fluid,) is calculated to be from fourteen to fifteen pounds avoirdupois on every square inch, (pure water, taking bulk for bulk, being about 828 times as heavy.) Now, reckoning the surface of a middle-sized man to be fourteen feet, he sustains the pressure of eleven tons. Many of our readers have seen the philosophical experiment of placing two hollow metallic hemispheres rim to rim, the rims being nicely adjusted and smeared with lard; this being done, the air, by means of a stop-cock on the lower hemisphere, screwed into a powerful air-pump apparatus, is drawn out or exhausted--the stop-cock is turned--the globe is unscrewed from the air-pump, and placed in the hands of those who may consent to try their strength in pulling the two hemispheres asunder. Enormous is the force required; if the diameter of the circle be fourteen inches, the least force that will separate them will be equivalent to half a ton. Such, then, being the pressure of the atmosphere, as is clearly proved by simple experiments, it may at first create some surprise that the human body is capable of sustaining it without being crushed; that the tiny insect, with its delicate wings--and in some these amount to several square inches of surface--is not reduced to atoms. But the wonder will cease, when we reflect that this pressure, or a pressure little short of it, is essential to the existence, not of man only, but of all terrestrial organic beings.