Page:Popular Science Monthly Volume 88.djvu/286

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��Popular Science Monthly

��How to Sit Straight and Still be Comfortable

THE ordinary straight-back chair encourages incorrect posture. It does not conform to the natural mould of the back. The sitter must assume a slouching attitude to be comfortable.

���The cushion fits into the small of the sitter's back and encourages him to sit upright with the chest properly raised

All this is remedied by a simple de- vice invented by Dr. J. H. Kellogg of Battle Creek, Michigan. The device is a small leather or cloth bound cushion which may be attached to any chair. This cushion is so placed that it fits into the small of the sitter's back and en- ables him to sit upright, with chest properly raised and at the same time to be comfortable.

Concrete to Replace Willow Mats

EXPERIMENTS have been made by the United States Bureau of Stand- ards to develop a method for accelerat- ing the hardening of concrete in order that concrete may be substituted for the willow mats that have been used in the past along the Mississippi River. As a result of the experiment, it was found that four per cent of calcium chloride added to the mixing water increases the strength of the one-day-old concrete one hundred per cent.

��Testing a Hack- Saw's Strength

IX order to prove that a hack saw is an instrument of remarkable tensile strength, an experiment was recently con- ducted at Springfield, Mass. It was found that the thin steel would sustain without injury two hundred and eighty- two pounds, the weight of two men.

Much damage is done to hack saws by too speedy operation, the operator often forgetting that it is the action, not the speed, that does the work. A hack saw should not be run faster than forty to sixty strokes a minute, and no blade will stand a higher speed without injury.

���The thin hack-saw, although bending

badly, is supporting two hundred and

eighty-two pounds without damage to

itself

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