Construction of the Barrel.
To those who are conversant with the principle of tl.e construction of barrels for organs, chimes. i e tit it r automatical engines, that which is necessary fo a • . pet dr:.w-looni, will not appear very difficult , bar. f r t c user of mechanics who may wish to tnn:t rsta I the , eipk. of this machine, it may perhal s be p r • r a little more into detail. The b. rrei may be 0 loss., built of thick and well se;.st lied plank r i t rs or wedged, or otherwise fir tixt t which may be either of that:cable or c.e-t no; : tit Lie is certainly pre feral le in est ry re sit a t. \\ n toe cover is firmly joined by glue an,d (4)1111it st. 4.. C it is to be very truly at.d straig. 11t tin!. . 4 Vi mete it can be done, this operath i NS be heat r performed in the bush es or centres it: ss ...let, it is :,ft Twards to revolve titan mew here. WI e t. u.is nas been done, it is only necessary to ascertain, t..c places for the projecting pins; and these will be much firmer and less liable to accident, if screwed, than if driven into the cover or circumference of the barrel. In order to ascertain with precision the proper diameter of the barrel, regard must previously be paid, 1st, To the extent or number of changes required in the pattern to be formed. This will be easily found by referring to the design, as in mounting the common car pet draw-loom ; for if the pattern is the same, just as many sets of forks or pins will be required for the power loom as there are bobs or handles for the common loom.
2dly, The range which is required to open the sheet each time to a sufficient depth ; and this may be found by attending to the principles upon which the agency of the barrel upon the mails of the harness depends. Let us suppose, for example, that the depth of shed formed by the harness requires that the mails should be lifted three inches. Then as this is to be effected by the devia tion of the tail part from the straight line, and that as one extremity of the harness only is moveable without enter ing into all the nicety of trigonometrical calculation, it may be assumed that the lashes will descend to raise the mails in the ratio of 2 to 1, or nearly so. If then the bar
rel must move six inches at every shift, a very large dia meter indeed would be required for a very moderate range of pattern ; and yet this, where it is practicable, will be by far the easiest and cheapest method. Taking, therefore, the shift of the barrel at six inches each, a barrel six feet in diameter would only work a pattern of about forty changes. But in more extensive patterns, the barrel must be extended to a size, which would be totally impracticable. 'Means must therefore be used to counteract this inconveniency, and fortunately these are simple and obvious. It is obvious, that in the way in which the lashes are fixed in the common carpet-loom, they are well calculated for their purpose ; for a child will find little inconvenience in pulling a handle six in ches down, but would find his strength totally inadequate to raise a great number of weights suspended to the har ness, were the mechanical power against him. Upon this obvious principle it is plain, that a few small blocks placed above the barrel, to invert the power and increase the range of the mails in rising, will at once do away the inconvenience, and consequently it will be easy to re duce the size of the barrel, and increase the range of the weights in whatever ratio may be found practically con venient. Where the agency of water or steam is employ the loss of power can be an object of no considera tion ; and no judicious mechanist can be at a moment's loss to construct them with any number of sheaves suited to his purpose. It is simply the apparatus employed to shorten the range of the weight which moves a common roasting jack. A few levers also might be very easily so disposed as to produce exactly the very same effect. For a cheap and simple practical substitute, large glass beads, with a proper number of smooth holes, and the cord rubbed with black lead, would do very well.