Page:Popular Science Monthly Volume 89.djvu/774

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��Popular Science Monthly

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��Show-Window Advertising Device

Operated by Gas Bubbles H K device

��acidulated water of the tank, gas coming oil froni the plate and rising so as to till the small bell.

��illustrated is based on the move- ment of a body caused by electro- lytic action. In a glass tank of liquid is placed a celluloid or other disk which floats upright. On its top is a small bell-shaped body of any material. A metal plate is mounted at the middle of the disk and a wire leads down from it and projects below the disk. The end of the wire dips into bottom of the tank,

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��The disk rises to the top of the tank where the gas escapes, causing the disk to sink

��mercury and thus

��at the makes

��electric contact so that an electrolytic action is set up.

The metal plate is attacked by the

��The gas contained in the bell increases the buoyancy of the float and causes it to rise to the top of the tank, where the gas escapes out of a fine tube at the top of the bell. The gas could not escape at the bot- tom due to capil- lary action, but at the toj) of the tank the end of the tube comes against blot- ting paper and the gas escapes because the capillary effect at the end of the tube is destroyed. When the gas escapes the float descends again to the bottom of the tank, and the action is repeated. An advertisement can be put on the disk, or letters can be used.

��Money Prizes for Motorcyclists

Send In Your Kinks

��IF you are a motorcyclist, if >U have devised simple wa>s of mak- ing repairs, if you have improved >(nir machine in any wa\-, this will interest you.

The Popular Science Moxthly offers a first prize of $25, a second jirize of $15 and a third prize of $10 for articles in which motorcyclists will describe and illustrate the methods which they ha\'e successfully cm- ])io\c'd for overcoming trouble, for making (|ui(k repairs by the roadside or more ditlicult repairs in the shop, or for making attachments broaden- ing the use of the motorcyle.

The three prizes will be awarded by the editors of the Poi'l'L.VK SciliNCE MoMULV in the order of merit. W iiat is more, even though your article ma>' not win a prize, the edi- tors may buy it at the usual rates, just licr.insc it is so good.

��There are no limitations to this prize offer. We don't care for fine ]ihrasing, init for mechanical ideas. Rough pencil drawings or jihotographs will do for illustrations.

ObserN'e these conditions:

(i) .Xrtick's must be written on one side of the .sheet only.

(2) Write your name and address in the

upper right-hand corner of the first sheet.

(3) Enclose postage for ihc return of llu-

manuscript.

(4) Don't send in arlicles on ideas which

have already been published.

(5) Uon't send paper ideas — tilings thai

you haven't aclualK' done \ourself.

(6) .Xcidress the envelopes containing

arlicles to

"Motorcycle Contest Editor"

I'lintAK Siii:\(ic MoNrnrv

239 Fourth Ave., New York City

The contt'st will close on ni'comhrr

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