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the facts of science, and the important truths of religion. We are only yet beginning to cast off the yoke of that ignorance, under the guise of wisdom, under which the men of other times bowed with such abject submission. Religious prejudices, in particular, derived from education and submission to mere authority, are frequently so strong that no species of reasoning, however convincing to an unbiased mind, is sufficient to subdue them. When certain dogmas or opinions, however futile, have got a firm hold on the mental faculties, all the arguments that can be derived from reason and philosophy, and even from the most cogent announcements of Divine revelation, are found altogether insufficient to displace them. And, as the fostering of erroneous opinions, in relation to religion, may endanger our best interests, both in relation to the life that now is and the life to come, it is of the utmost importance to all, and especially to young persons, that they examine, with care and without prejudice, every doctrine and opinion they embrace, without regard to human authority; founding all their views and sentiments on the dictates of enlightened reason, and the plain declarations of the word of God.

From what has been now stated, we may easily compute the weight sustained by the body of a middle-sized man, in consequence of the pressure of the atmosphere. Suppose the average stature of the human body to be about five feet nine inches; suppose the breadth in

front to be about one foot, and the breadth on each side half a foot; by allowing a little deduction for the narrowness of the head and feet, we may reckon about five feet in front, and five for the back part, and two and a half square feet for each side of the body, or fifteen square feet in all. It has already been stated that the atmospheric pressure on one square foot is 2,160 pounds. Multiply this sum by fifteen, the number of square feet on the surface of the human body, and the product will be 32,400 pounds, or somewhat more than fourteen tons, or the weight of more than fourteen ordinary cart-loads of heavy goods. This is the pressure sustained by every middle-sized mana pressure which would be insupportable, and even crush us to pieces, were it not that it is equal in every part; pressing with the same force upwards, downwards, and on every side; and is, at the same time, counterbalanced by the spring of the air within us, which is diffused through the whole body, and re-acts with an equal force against the outward pressure. This pressure, however, is somewhat different at different times. When the air is lightest, the pressure is 31,150 pounds, and, when heaviest, about 33,660 pounds, making a difference of about 2,500 pounds, the weight with which we are compressed more at one time than at another. This great difference in the atmospheric pressure is found greatly to affect the animal functions and the state of health. A person labouring under an asthmatical com

plaint will find his disorder increased when the air is light, as it has then less elasticity, and is not so capable of expanding the lungs. The air is generally lightest in hazy and rainy weather, when the clouds descend, and the mists cover the mountain tops. Every one then feels the effect, by a certain degree of lassitude and depression of spirits, occasioned by the surrounding gloom, and by being deprived of an atmospheric pressure amounting to more than 2,000 pounds. The fibres of the body are relaxed, the contractile force of the muscles diminished, and a languid circulation of the fluids ensues, which sometimes produce obstructions, fevers, and headaches; and, in most persons, a sort of indolence and gloomy inactivity. Whereas, when the air is heavy, and the clouds ascend to the higher regions, and appear like fine fleeces on the blue vault of heaven, the nerves and fibres of the animal system are braced by the additional pressure of the atmosphere, the blood-vessels exert their full power, the solids are compressed, the fluids circulate with increased vigour, we feel light and alert, and the elevation of the animal spirits is increased by the splendour and activity of the surrounding scene.

Weight of the whole atmosphere.-From the facts now stated, we may form an estimate of the weight of the whole body of the atmosphere which surrounds the surface of the earth. The surface of the globe contains, in round numbers, 200,000,000 of square miles; every

square mile contains 27,878,400 square feet; and these two numbers multiplied together, produce 5,575,680,000,000,000; or, five thousand five hundred and seventy-five billions, six hundred and eighty thousand millions, equal to the number of square feet on the surface of the earth; which, multiplied by 2,160 pounds, (equal to the pressure on every square foot,) produces the sum of 12,043,468,800,000,000,000; that is, twelve trillions, forty-three thousand four hundred and sixty-eight billions, and eight hundred thousand millions; which is equal to the number of pounds which constitute the weight of the whole atmosphere, or 5,000,000,000,000,000; that is, about five thousand billions of tons. A more definite idea of this weight may be obtained by supposing a ball of lead, extending from London to Oxford, stretching sixty miles perpendicularly above us, and in every direction; or, in other words, a ball of lead one hundred and ninety miles in circumference, and about sixty miles in diameter. Suppose this ball placed on one end of an immense balance, and the whole atmosphere on the other, they would nearly counterpoise each other. So that this invisible fluid, which we are apt to consider as almost a nonentity, when considered as a whole, contains a weight which it is difficult for numbers to express.

It need only be observed further on this point, that the air decreases in density in proportion as we ascend to the higher regions of

the atmosphere. At the height of seven miles, the air is four times rarer than at the surface of the earth; at the height of fourteen miles, it is sixteen times rarer; at the height of twentyeight miles, it is two hundred and fifty-six times rarer; at the height of ninety-six miles, it is 268,435,456 times rarer; and, at the height of five hundred miles, it has been computed, that a cubic inch of such air as we breathe at the surface of the earth, would be so much rarefied, that it would fill a hollow sphere equal in diameter to the orbit of the planet Saturn, which is 1,800,000,000 of miles in diameter. This is a necessary consequence of the elasticity of the air, and of its want of compression in the higher regions; and that this is in reality the case, is proved by experiment as well as by calculation. When we take a barometer to the top of a mountain only half a mile in perpendicular elevation, the mercury falls from thirty to twenty-seven inches; and the fall of the mercury is in proportion the higher we ascend. Those travellers who have climbed to the tops of lofty mountains know, by experience, that the air is much thinner in those regions than in the plains below. Their breathing becomes difficult and painful, their hands and feet swell, and they are sometimes seized with a vomiting of blood. They also find, that the atmosphere becomes clearer as they ascend, and is unable to support the clouds. We are informed by Don Ulloa that, while he stood on the top of the Andes, in

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