the ground, and e AN INQUIRY INTO THE STRENGTH OF MAN 263 SES air, by a large ground plained, the effort of the muscles of in the cording to what we have before ex the belly, and. end to hooks, of two little cords, at each his legs being able to raise a weight of 150lbs. only to the height of two at the end erande of small or three inches, be could not raise on each side of the head of this young gfellow and all his strength depended on the muscles of the shoulders and loins, for he stooped at first, whilst the hooks were fastened to the girt, and afterwards he lifted the animal off ground, leaning his hands upon his knees. He again raised, in the same manner, other burdens, which seemed heavier than this animal, and said he found less difficulty in it, because the ass struggled when it was off the ground.qu574 104 261 909 How examine the effort of a man to folgrew to carry & Burden o on his is shoulders: say the weight of this burden may be 150lbs., and that he can walk with this load easily enough on a horizontal plane, provided he does not Quake great strides but he cannot go, up a hill" ladder with the game weight, for the action of walk Ing with a burden on the shoulders, be considered as the circular notion of the centre of gravity of the body an and of the weight joined Together on the foot which advances, as the centre e of the arch of motion, the effort of the muscles of the other Jeg serving only to push the centre 3頂 forwards, and if the arch described DV this ntre is small, the effort of wake the hinder leg must not be great to ake it be described, seeing the Whole burden of the body, and of the Weight, is not is not to be raised by more than the versed sine of half the arch, which is not considerable in this case, with regard to the arch which is the path in which the whole burden advances. Thus we see, that a bman Well loaded can walk the more easily, as he makes less strides, see sing the sine will be so much the less, and that he could not advance by making large strides; that of the hinder leg 'could not it to five inches, which is the height of the usual steps; nor go up a hill, without making such short steps as to rise but two or three inches at each. It therefore now remains for me only to consider the effort of a man to draw or push horizontally. To render this explication/more clear and intelligible, I consider his strength applied to the handled of a roller, the axis of which is horizontal, and over which a cord is turned which sustains a weight; having supposed the distance from the centre of the roller to the elbow of the handle equal to the semidiameter of the roller, that the force may be compared, being applied, without any augmentation, on the side of the machine; I have also had no regard to the friction of the axis of the roller, nor to the difficulty which the cord may have to bend seist 1 H First, it is evident, that if the elbow of the handle is placed horizontally, and that is about the height of the knees, the effort of the man who raises it in drawing may, at the same time, lift the weight of 150lbs. which shall be fastened to other extremity of the cord, taking all possible advantages, seeing it is the same as to raise the weight, as I have already explained. But if it is to depress the handle, his effort can be no more than 140lbs., which is the weight of his whole body, that the can apply by bearing upon it, unless he is loaded, for then he could make a much greater effort, a 20 bur Secondly, if the elbow of the handle is placed vertically, and is at the height of the shoulders, it is certain that a man can make no effort to turn it, by drawing it or pushing it with his hands, if the two feet are t raise the straight, which, and the body burden of the body and of the weight, AN INQUIRY INTO THE STRENGTH OF MAN, effort to push or draw, which is known by mechanics; for I consider the breadth of the feet only as a single point, P. But if the handle is higher or lower than the height of the shoulders, then the line which goes from the shoulders to the hands, which is AM, and that which goes from the shoulders to the end of the feet, which here is AP, will make an obtuse or an acute angle, and the man may have some force to draw or push the handle, and this force depends wholly on the weight of the body, as is easy to know and demonstrate, and this weight, or this force, must be considered as reunited in his centre of gravity, which is near the navel, within the body; I say, that regard must be had only to the weight of the body to determine the equilibrium, for the effort of the muscles of the leg and thighs serves only to preserve this equilibrium in walking. Fig 2. Let the handle, Dobe at the height of the shoulders, A, and let the centre of gravity of the body be at C, the body being much inclined towards the handle, but let the end of the feet beat P.We must consider, first, this point, P, as the fulerum of a lever, or straight rod, PCH, which passing through the centre of gravity, C, of the whole body, meets the line of the farms, MA, at the point, H; secondly, that this point, C, of the slever being loaded with the weight of all the body, 140lbs., with its natural direc tion, its extremity, H, is sustained with the horizontal direction, MAH; whence it is easy to conclude, by me. chanies, what effort the weight cof the body at C, with its natural dis rection, can make on the handle, ac cording to the horizontal direction, DH. For, first, let /PH be of 240 parts, and PC of 80; since the effort of all the body at the point, Os ds 140lbs., it will be but 80lbs at the Point H; as if, at the point H, there were a weight of 80lbs. suspended with its natural direction, which must be, on the supposition that we have made, perpendicular to MA Wherefore, if ve draws from the point of support, P, the line PF perpendicular to MAF, the weight of 80lbs. at H, with its natural direc tiot, will be to the effort of the same according to the horizontal di rection, MAH, on the handle, in the ratio of PF to HF, which very much diminishes the effort of the 80lbs. in a moderate inclination of the body, ACB. And if we suppose, for instance, that the line PCH makes with MAF the angle PHF, of 70 de grees, the line of the body, ACB, will then be inclined to the horizon, or with MF, an angle of more than 60 degrees, which is at most the ins clination in which the body can be able to walk; and the sine of 70 de erom Isinulle grees, which is PF, will be to the sine of its complement, which is HF, very nearly as three to one; and, con sequently the effort of the 80lbs. at H, according to the natural direc tion, will be to that which they make according to the horizontal direc tion, only one third of 80lbs., which 18 little less than 27lbs. Those who have not made the experiment of the strength of a man, to push horizontally with the arms, or to draw a horizontal cord in walk ing, the body being inclined for wards, whether the cord be fastened towards the shoulders or about the middle of othe body (for the effort will be no greater in the same in elination of the body, since the sinesing animals, but as it does not en of inclination and their complements are always in the same ratio), cannot persuade themselves that the whole strength of a man is reduced to draw only 27lbs. with a horizontal direction.si Noti but a man, being bent, can sustain as much greater weight than 27lbs. seeing, if the line PH made with HF an angle of 45 de grees, it is certain that the weight ofs the body would sustain 70lbs; but as he would be bent according to a line, as AB, which would be much more inclined to the horizon than 45 degrees, it is certain that, far from being able to walk, he would hardly be able to sustain it. The same demonstration serves also to show, that a man will have much more strength to draw in walking backwards than forwards; for, in this situation of the body, the line PCH, fig. 3, which passes from the end of the feet, P, through the centre of gravity, C, and whereon depends the augmentation of the force, will be always more inclined to the horizon than the line of the body, ACB quite contrary to what it is in the preceding position. But this manner of drawing could not be put in practice, unless it was only to draw a cord, the man continuing al ways in the same plane; and one should not fail of putting one's self in this posture in such a case, for nature and experience have taught us to take always all possible advan tage in common operations. It is for the same reason,s also, that our mariners, and, in general, all who rowl on the sea, always pull their oars from before backwards, for they have much more force than if they pushed them forwards, as the gon doliers of Venice do, for which I see no other reason than that of seeing before them; which is much more necessary for their than great force, ON THE IMPROVEMENT OF LIGHT- and of a con 15h 9labimHOUSES; BY SIR JOSEPH SENHOUSE. 2013 SIR,-Although great improvements have, of late years, been made through out the British dominions upon Light Houses, yet I think it is possible to make farther progress in so useful and necessary a building. "} In the first place, I would propose that every light-house should have a different colour, as red, yellow, blue, &c., by which means they would be immediately identified at night, as soon as perceived, which cannot so certainly be done if they are all alike in that respect. In the next place, I would recom mend that they should be so constructed as not only to ascertain the situation of headlands, harbours, &c., but also to determine the distance the observer may be from them, in the following manner, viz. эт at Amaya be at B being 100, 150, or 200 feet distant, easy Jam, Sirious sibeen The unisd Yours well-wisherpoq llama 1 10 2099907g JoŠENHOUSE.OJ Hensingham Hall, near Whitehaven, u June 8th, 1825.b To 12iom v6 1062719968_3d yam siedqzomis eGut199 and ; ebilevai d to ysilitu 27903 59 EAPING CORN. Song olevad 20 hso091190 The French claim the merit of a new discovery of great importance to agriculture in the advantages which, according to them, result from the practice of reaping corn before it is perfectly ripe. This theory, which has just been promulgated by M. Cadet de Vaux, originates with M. de Salles, of the Agricultural Society of Beziers. The exolion silt ve batquoo Asten he following are the particulars Corn reaped eight days before the usual time is, in the first place, secured from the dangers which threaten it at that time this is only accidental; but a positive advantage is, that the grain is fuller, larger, finer, and that It is never attacked by the we weevil. The truth of these statements has been proved by the most conclusive comparative experiments suponds a piece of corn, one-half of which was reaped before the usual time, and the other half at the degree of matu rity fixed by the ordinary practice. The first portion gave a corn more for half a hectare of land. Afterwards, an equal quantity of flour from the wheat of each portion Twas made into bread; that of the corn reaped green gaye seven pounds of bread more than the other in six decalitres. Lastly, the weevil attacked the corn which was cut ripe, the other was exempt fro from it. The DAMP-DETECTOR-IMPROVED AMERICAN STEAM-BOAT, ETC. 267 proper time for reaping is that when 1 هذا از le signs DAMP-DETECTOR. An ingenious little instrument under this name, which denotes its use, has been invented by Mr. Essex. It consists of a small ivory box, about an inch in diameter, in which is a needle turning on a pivot, like the small pocket compasses. Being set to zero, it either proceeds or recedes as the surrounding atmosphere is moist or dry. Thus the state of the atmosphere may b be ascertained by invalids; but, perhaps, the greatest utility of the instrument can be experienced by travellers, since, by placing it for a few minutes only Between bed-clothes or wearingapparel, the motion of the index certainly detects the existence of damp, if there be any present. ༣ བྷཱཛྫཱ ཚཱ ཉྩ ༧ པ ཨ -lumong used taminal do, an -igio zus sb 39bc) I -LONDON MECHANICS' INSTITUTION, SIR,Allow me to request that you will correct an error which appears in igour Magazine of the 16th inst. Speak hing of the new Theatre of the London Mechanics' Institution, you say (page 232) The construction of the buildsing does 46 0 one of the Vice-Presi 9 York; and believing that you are From the Philadelphia Freeman's Journal of April 20. THE TRENTON STEAM-BOAT.The Trenton is constructed upon an entire new model. Her boilers rest upon the guards projecting over the water from each side of the boat. This leaves the deck entirely unobstructed, and forms what may be The called a promenade deck. space usually occupied by the boilers is converted into convenient and elegant dressing-rooms. Should any accident happen to the boilers, the water would be thrown directly into Mr. MWfat credit to its designer, the river, and not in the least en- he 19 moiting dose to isodwodt mod T 9MPROVED AMERICAN STEAM-BOAT. 2 was looking over an xis 9 newspaper a short time since, I was much pleased with the following description of a new Steam-Boat, recently built at or near New danger the passengers. And what is likewise important, the unpleasant and annoying degree of heat in the dining cabins is no longer felt. She was built at Hoboken, and it may be fearlessly asserted, the improvements in the arrangement and disposition of her machinery are far greater than any that have been yet made since the first introduction of these boats into our waters. She might not unaptly be called the Water Travelling Balloon MR. BADNALL'S PATENT THROWING SIR, I observe in your Number of the 2d inst. some observations by |