your friend,
YANKEE.
In answer to the foregoing, we would remind our correspondent, that in his former communication, he proposed a limited weight of apparatus, and in our answer, it was far from our intention to allow an additional weight on account of the requisite extent of surface. With regard to the philosophy of the flight of the eagle, it must be borne in mind that atmospheric resistance is as the square of the velocitydownwardand the only way in which the phenomenon of the flight of the eagle can be reconciled with the laws of mechanical science as established by experiment, is by supposing the velocity of the wing downward to be equal to 70 feet per second, whereby a resistance would be encountered equal to 12 pounds per square foot of surface to the wings. It is a fact, however, that kites, and hawks are often seen to continue suspended in the air several minutes without any apparent motion of the wings; but by what law or theory the feat is accomplished, natural philosophy has ventured no other conjecture than that the bird is endowed with the faculty of suspending occasionally its ordinary subjection to the laws of gravity. If any observing theorist will give any more rational conjecture on the subject, we should be glad to have him examine it.
It is proposed and urged by the papers in several States, to have a thanksgiving day throughout the Union, on the 26th of November.
"As dull as a hoe," is a very common phrase, and implies that hoes are necessarily or ordinarily dull. But it is advisible for farmers to keep their hoes sharp, as they regard a saving of labor.
conical windlass
Various methods have been heretofore described, for raising heavy bodies, or producing for other purposes, a great force,--usually miscalled power--by the application of a comparatively small force: but no method is known, more unlimited in its effect, or more simple in construction; than the conical windlass. It consists of a simple horizontal windlass, with a crank at one end, as shown in the engraving. The windlass is made in a conical form, being a little larger at one end, than at the other; and if the friction of its bearings be relieved by the ordinary friction rollers, it will so far multiply the force applied, as to break a double inch-rope, by the power of one man at the crank. An endless rope, or one of which the two ends are spliced together, is passed five or six times round the small end of the windlass, and down under a single pulley below: then, as the windlass is turned by the crank, the rope is constantly given off from one part, while the circumference is greater. Now it is plain, that if the windlass is one-fifth of an inch larger in circumference, at the point at which the rope is taken up, than at the place where it is given off to the pulley, that whatever may be appended thereto, will be raised one tenth of an inch by each revolution Then, if we suppose the crank lever to be fifteen inches, the handle will travel about 100 inches, in each revolution, which gives a power, or increase of force, of 1000 to one. Therefore, if 100 pounds of power be applied to the crank handle, it will be sufficient--minus friction--to raise a weight of 100,000 lbs. The only inconvenience in this apparatus, and which prevents its coming into more general use, is, that it is too limited in the extent of its motion, in consequence of the travelling of the rope from one end of the windlass to the other. Thus, if the windlass be but twenty-five inches long, and the rope one inch in diameter, it will admit only twenty revolutions, without renewing. Yet, in many cases, in which an article in required to be raised, or moved but a few inches, the conical windlass will be found preferable to any other method.
Our correspondent S. B. cannot comprehend that the strength of iron for a cylindrical boiler should be in direct proportion to the diameter thereof, in order to sustain an equal pressure per square inch; wherefore, we must reason with him on the long scale. The cohesive strength of good iron is 64,000 lbs. per square inch; and of course, a strip of boiler-iron plate 1/8th inch thick will sustain 8000 lbs. If a boiler made of thin iron is 14 inches in diameter, or 44 inches in circumference, each inch of its length will contain 44 square inches, and either half thereof will contain 22 inches, and as the pressure on this portion is sustained by at least two inches of width of plate,--one inch on each side,--it follows that it will sustain a pressure of at least 700 lbs. per square inch, in the direction of circumference. If the diameter is double, the number of square inches will be double, and will require double the thickness to sustain equal pressure. With regard to the pressure endwise, the area of a cylinder head 14 inches in diameter is 154 inches, and the strength of the 44 inches of circumference would be sufficient to sustain 352,000 lbs., which, divided by the area, is 2,275 lbs. per square inch. If the diameter is 56 inches, the circumference being 172, would sustain a pressure endwise of 555 lbs. per inch. Thus it will be seen that if the cylinder were even 20 feet in diameter, the iron would better sustain the pressure on the head that on the periphery. With regard to the requisite strength of the cylinder's head, if they are made in a semi-spherical convex form, they will require no more thickness of plate than the cylinder: but if they consist of plane disks, the thickness thereof should bear the same proportion to that of the periphery that the area in square inches does to three times the circumference. But in general, no other rule is observed for the thickness of the heads, than to make them extravagantly heavy, without much regard to theoretic calculation.
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A gentleman who resided some time on one of the West India Islands informs us that while he was once travelling along the bed of a deep ravine overhung with thick vines, he was actually startled by the immense numbers of humming birds which hovered over and about him. They hovered about him as if actuated by curiosity alone. They were of various kinds and colors, some of them being nearly as large as sparrows, while others were but little larger than a bee. Some were of a dingy green, or a light brown, while others seemed gaudily arrayed in plumage as brilliant and variegated as the rainbow. They would approach within arms length of his face, and pausing in their flight, with their little wings, in rapid motion, would stare at him as if they wondered what possible business he could have in those remote wilds; but they exhibited no symptoms of terror, not having been taught by experience to fear the cruelty of man.
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Transcriber's Note: Obvious typos have been corrected without comment, except in articles where they are intended to be displayed.
The title to an illustrated article has been interpolated as "The Regulator", where no title previously was, based upon an assumption from the partially obliterated caption to the accompanying illustration.