Page:Popular Science Monthly Volume 89.djvu/660

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��Pupular Science Montlilij

��COUNTING DEVICE .REMOVABLE CAP CLAMP

���A mechan- ism in the handle counts the jumps

Letting the Jumping Rope Record the Jumps

Al.l. the vocal gymnastics . have been taken out of the youthful pastime of jump- ing rope. No longer will numbers be called as the prod- igy next door jumps up to five hundred or more, and the chances are that "Pepper, sail, mustard, cider, vinegar," will be forgotten. Two inventors ot New Brunswick, New Jersey, Edward H. Stokes anci Ray- mond E. Grymes, have inven- ted a jumi^ing-rope wJiich will automatically rejiister the num- ber of times it is turncil. In other words, children can jump themselves to death without uttering a sound.

In a handle at one end of the jumping-rope is a counting mechanism which registers each turn of the rope. The handle is hollow so that the rope enters it and connects with the counter at the front end. A removable cap makes it possible to adjust the coun- ter. A sight opening is provided in the side of the handle to enable the jumper to note the nuniber (if I urns.

��i dangerous ns is exciting

��Why You Hear Well on a Clear, Frosty Night

S( lENCE says that the loudness of xiunds varies inversely as the square ot the distance. This is merely another way of saying that if you walk three times as far away from the source of the sound as you were liefore, its loudness will be not one-third what it was, but one-ninth what it was, for nine is the fquare of three.

On the other hand, the density of the medium which conveys sound is very im- portant. On a frosty night the air is dense. One consequence of this is that an automobile runs better, because the engine gets larger supplies of oxygen. Another result is that sounds are heard luore loudly. Howexer, the report of a gun high up in the mountains is like the sound of an exploded firecracker. In the Colorado Rockies giant boulders are carried along b\' snow slides. On a warm night the slides make little noise, but on a clear, frosty night the noi-^^e is deafening.

��Increasing the Thrills in Ice- Skating

SKlI.Fbb skating on ice is tlilVicult enough with ordi- iiar\- skates but with stilt-skates, such as those illustrated, it is in a class with dangerous sports. The ice is hard enough w hen hit frt)m the usual height. How must it feel when stilt-skates skid out from under yoii?

There arc only three people in the United States who have attained proficiency in the art of skating on stilts. C. P. Mul- d- are just as safe as ordinar>- ice-skates, and the>' give just as nuich jileasure and comfort. There is no dciuing the fact that they afford |)leasure; but as for com- fort — that is for professionals.

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