Kindly keep your qneries o n separate sheets of paper when corresponding about such matters as paten ts. subscriptions, books. etc. This ",HI vreatIv facilitate answering your quesions, as in many cases they have to be referred to experts. The full name and address should be given on every sheet. No attention will be paid to unsigned q ueries. Full hints to correspondents are printed from time to time and will be mailed on request. (12576) L. W. asks: Will you please give me a clear definition of “power factor” and “KVA,” expressions used in electrotech-nics, and illustrate same by example? A. “The 'power factor' of an alternating current circuit, or apparatus, is the ratio of the electric power in watts to the apparent power in volt-amperes.” This is the definition as given In the Standardization Rules of the American Institute of Electrical Engineers. It Is official. The true power of an alternating current divided by the apparent power, which is the volt-amperes entering the apparatus, gives the power factor. The volt-amperes apparently entering the apparatus multiplied by the power factor give the true power of the apparatus, The apparent power is the KVA, the kilo-volt-amperes. You will find this fully explained In Sloane's “Handy Book,” which we can furnish you for $3.50. (12577) W. D. C. asks: Why does the honeysuckle vine grow to the left just contrary to the growth of all other trailing vege-ta tion ? All vines seek the sun or grow to the right, except the honeysuckle. Why is this? A. Many plants twine in the spiral of a right-handed screw, or “against the sun,” or “from left to right.” The common garden bean and the wisteria have this habit. Other plants like the hop and honeysuckle twine In the opposite direction, presenting the spiral of a left-handed screw, A most interesting account of these phenomena will be found in Darwin's “Movements and Habits of Climbing Plants." (12578) F. L. Y. asks: How high does a person have to go before the earth becomes invisible to the sight? A. Any object is just visible which fills; one minute of arc. The earth will subtend an angle of one minute at a distance of a little more than 27,000,000 miles, and hence would be visible as a point at that distance, but would not show any disk. (12579) D. E, says: I notice in a recent number of your paper an item in which you say that some process of restoring the appearance of a felt hat, that had become somewhat rusty, would fill a long “felt” want. I have solved this problem by wiping my hat with the same cloth I polish my shoes with. The blacking I use does not “crock” when applied to the hat, and an occasional application keeps it looking nice. (12580) R. F. McK. says: Please give me a solution of the following : If a tube 3 feet high and 6 inches in diameter is filled with water, and has a plunger in the bottom 1 inch in diameter, will the force required to push the plunger up in the tube 1 inch equal the force required to lift a column of water 1 inch in diameter and 3 feet high to the height of 1 inch? A. The pressure of water in the tube is equal in all direction at any given point. At the moment your plunger starts to rise, it is resisted by a head of 3 feet of water, that is, by the weight of a column of water 3 feet high and the area of the plunger. But as the plunger rises, the height of the column decreases. If you had a tube around the plunger, raising the plunger I inch would raise the whole body of the water in the tube 1 inch, and the plunger would operate under a constant pressure equal to 3 feet head of water ; but in the illustration you give the rise of the plunger of 1 inch will cause a very much smaller rise of the surface of the water, so that when the plunger has completed its lift of 1 inch it will have little more than 35 inches of head of water above it, and the average pressure will therefore be about 35 % inches of water. Obviously, if your plunger traveled the whole 3 feet and came to the surface of the water at the completion of the 3-foot travel, there would be no pressure against the plunger due to water head, since the plunger would emerge from the surface of the water. Similarly, the pressure on the plunger decreases with every inch of its travel upward. (12581) J. C. J. asks: If a substance could be found which is heavier than water and less compressible, would it sink in any depth of water? A. If a substance could he found which ' is slightly heavier but less compressible than water, it might sink in water till it had reached the place where it was of the same density as the water at that place and there remain. The water at the bottom of the ocean is about 1/20 denser than at the surface; hence this supposed material could not be as much as 1/20 heavier than water at the surface of the ocean. No such material II known to exist. Thinking” of Gifts- Think of Pens. -Thinking” of Pens-Think of "THERE is nothing that can show more consideration for beauty, service and quality. A useful present that is easy to buy and send. Made in sizes and styles to suit every hand and writing requirement. There are plain pens and diamond-mounted pens and all intermediates, to suit your purse and the occasion. There is the same superiority in all. Fountain Pens, to be satisfactory and permanent, must have the patented parts found only in those bearing the trade-mark Waterman's Ideal. Fine, medium, coarse, stub and oblique points. Avoid Substitutes—Illustrated Book on Request. SOLD BY THE BEST DEALERS-EVERYWHERE L. E. Waterman Company 173 BROADWAY, NEW YORK How to Double the Life of Your Light Delivery Car Take offf solid tires—put on Motz Cushion Tires. Thus' save your car from a thousand bumps and jolts each day and save yourself 75 % in upkeep cost. Your car thus equipped will give you two years' service where it would have given you but one before. For the Motz Cushion Tire is lively. It has the ra///V«ry of a properly inflated pneumatic, and the durability of the average solid tire. These combined features make it the only tire for light delivery cars. THE MOTZ CUSHION TIRE Observe in the illustration above, the three special features in Motz Cushion Tires which give them pneumatic resiliency and also do away with skidding: DOUBLE TREADS — UNDERCUT SIDES — SLANT-WISE BRIDGES These are patented features found only on Motz Cushion Tires. The Motz Cushion Tire is quick detachable. Fits any universal clincher or demountable rim. No trouble to apply. No removing wheels in replacing tires. No loss of time. If you have heavy duty trucks, you need Motz Demountable Solid tires. They possess the same quick-detachable feature as the Motz Cushion Tire. Let us send you more facts and figures showing the economy of Motz Cushion and Solid Tires. They mean a big saving to any' one who operates commercial cars. In writing, please ask for Booklet 93. THE MOTZ TIRE&RUBBER CO. Factories and Executive Office, AKRON, OHIO Branches: Chfcaso. 2023 Micblsan Ave.; Detroit. 999 Woodward Ave.; Kansas City, 409 East lStb Street I New York City. 1737 BroadWIf