The Expansion and Contraction of the Ropes Keep the Disk Up and to One Side of the Center
The shaft A is supported on the edges, in the bearings B and C, of a tank, D. A disk, E, having a central hole larger in diameter than the shaft, is located at the middle of the latter. The disk is supported by 12 or more cotton ropes, F. The tank is filled to the level G with water. The lower ropes, being immersed in the water, shrink and lift the disk slightly above the center in the position of an eccentric, as shown by the dotted lines in the sketch. The center of gravity of the disk in this position, being higher and slightly to one side of the shaft, the disk has a tendency to turn around. The motion drives the next rope into the water where it becomes soaked and shrinkage takes place again, lifting the disk to a higher position, while the rope coming out of the water dries out. The ropes emerging from the water but not yet thoroughly dry cause the upper part of the disk to be in an eccentric position laterally with reference to the center of the shaft, thus causing the center of gravity to be not only above but also slightly to one side.—Contributed by Charles Roberts, Brooklyn, N. Y.
A Paper-Bag Holder
A holder, to accommodate the different-sized bags used in a store, can be easily made of a board, 6 in. wide and 30 in. long. One edge of the board is cut with notches similar to the teeth of a ripsaw and their back-sloping edges are drilled to admit a nail point. A sufficient quantity of bags is placed in a pile and a nail is driven through the edge near their upper ends, and the projecting point of the nail is stuck into one of the holes. Proceed in the same manner with bags of other sizes. To remove a bag, take hold of the lower end of the outermost one and tear it from the nail. Be sure to drive the nails through the bags close to the top.—Contributed by Abner B. Shaw, N. Dartmouth, Mass.
Covering for Chalk Trays
The chalk trays fitted at the lower edge of blackboards soon collect considerable chalk dust and the chalk sticks dropped into it are, therefore, disagreeable to handle. A simple way of keeping the sticks clean is to cover the trays with wire mesh which is shaped like a tray but not so deep as the chalk tray. Thus the chalk dust will fall through this screen and be out of the way of the sticks.
A Curtain Hanger
A close-coiled spring, about 1/4 in. in diameter, makes a much better hanger for a short curtain than a small rod. The spring should be about 1 in. shorter than the width of the window and fastened with screwhooks. The spring is preferable not only because it is less apt to tear the fabric, as it will give some if the curtain is pulled, but also for the reason that it is much easier to put it through the hem than the rod.—Contributed by Walter Ramm, New York City.