APRII.. 0 E R 25'M. ELECTRICAL 1 ünP. EXPERIMENTER SCIENCE AND INVENTION VATCHING PLANTS, GROW SEE PAGE 1246 April, 1920 ELECTRICAL EXPERIMENTER 1225 "Your spare time is your ELECTRICITY capital :" as experts know it VOU do not have tó take time off from work and spend several 1 hundred dollars in tuition in order to master the practical side of electricity. The whole subject is now covered in a low- priced set of books, flexibly -bound and handy pocket -sized. st a few minutes of your spare time spent with the Croft Library of Practical Elec- ,tricity -each day will give you a know- ledge which could otherwise be gained only in years of practice. Earn a big salary The salaries of electrical workers are high and constantly going up. And the demand for properly trained men is more insistent than ever before in the history of electricity. 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You pay only $20 for a Terrell Croft, procured his knowledge with his sleeves rolled up. com- He was trouble shooter, draftsman, plete electrical education. Return the books at our ex- wireman, central station pense operator -then electrical engineer for the Westinghouse Com- if not entirely pleased. pany, He is a practical man and knòws the exact wants of his fellows workers. He tells of the short cuts to bigger pay, of the why and how of everything in electrical practice today. of 8 Volumes A letter that means something to YOU - McGRAW -HILL BOOK COMPANY, Flexibly bound Inc., 239 W. 39th St., New York, N.Y. Pocket Size Gentlemen: -In an attempt to ex- EXAMINATION COUPON 3000 pages press myself about CROFT'S NEW LIBRARY OF PRACTICAL ELEC- t 2100 TRIriTY, I have nevar seen, and do - - - - -- not L^lieve there was ever printed in t illustrations tbhna glish language, a more compre- t McGraw -Hill Book Co., Inc. Everything hr e set of books. It is a library 239 W. 39th St., New York is just as valuable to the novice you must know .s to the expert, because it is all prac- Gentlemen: -Please send me the Library of Practical Electricity (ship- tice. ping charges prepaid), for 10 days' free examination. If satisfactory about Respectfully, I will send $2 in ten days and $3 per month until $20 has been paid. If not wanted, I will write you for return shipping instructions. electricity at GUY H. PEIFER, the finger's end Chief, Doplan Silk Corporation, Name Hazelton, Pa. Home Address McGraw -Hill Book Co., Inc. City and State 239 West 39th Street New York 1 Where Employed Occupation (Ex.4.20) You benefit by mentioning the "Electrical Experimenter" when writing to advertisers. Electrical Experimenter 233 FULTON STREET, NEW YORK 233 Fulton Street, New York. Publisht ay Experimenter Publishing Company, Inc. (H. Gernsback, President; S. Gernsback, Treasurer; R. W. DeMott, Sec'y), EDITORI The Earqh90 IIIIIIIIIIIIIIIIIIIIIIÌIIÌI, 91111111111 IIIN IlrllerIlcar Mullen.? ANY things that we take for granted some- that there is no such tide in the interior of the earth. times turn out to be very much different If there were, the crust of the earth, due to the tidal than we first thought them to be. Take effects of the moon and the sun, would constantly rise for instance the earth's interior. Our and fall, for one thing, and we would have extensive physics instructors and scientists taught us daily earthquakes. But, you will say, the earth's crust for years that the earth was once a huge is so solid that there may well exist a tide inside of molten sphere, just beginning to cool down. The in- the earth that we cannot perceive. This is hardly even terior and center is supposed to be entirely fluid -a probable, however, because in that case the gigantic huge molten mass where all the known elements "in- tidal; effects created -a million times greater than any cluding rocks" are in a liquid state, at a tremendously ocean tide-would burst thru the earth's crust in short high temperature running up into thousands of degrees order. Do not forget that if the orange peel analogy Fahrenheit. Our physics instructors by way of im- holds good, there will be a liquid mass some 7,000 tell us that the hard crust miles deep! Contrast that with the average depth of pressing us were wont to figure out of the earth is just about as thick in proportion to the ocean of less than one mile and then is to an orange. the gigantic tides. a liquid interior would produce! the rest of the earth as the peel He And in order that we could not doubt their words But our modern scientist does not stop there. our instructors give us "proofs" to back up their con- goes and counts the very few active volcanoes and finds that as ventholes for a molten globe 7,000 miles tentions. few First, we are pointed out that the volcanoes -the in diameter, they appear preposterous. These earth's interior -prove that holes could no more serve as vents for this big globe ventholes of the liquid straw. the earth is fluid inside. Witness the many volcanic than you could vent an armory with a soda eruptions belching forth molten rock, lava and brim- On top of this our astronomers come along and stone. And to further disarm our suspicions we are prove mathematically, without a shade of doubt, that shown that as we descend into the earth's interior, the the earth is at least as rigid as steel. temperature rises one degree Fahrenheit for every 40 But how explain the volcanoes and our deep hot feet. It matters not where we bore a hole or shafts? Our scientists prefer to think-and they can to 50 interior is not molten. interior ; the rise of tem- prove it, too, that the earth's sink a shaft into the earth's local molten perature as we descend is pretty uniform the world The volcanoes are merely ventholes for over, even in high latitudes. These are both facts, well pockets. The earth's heat is produced by radium, or authenticated and are not doubted by any sane person. rather radioactivity. And while the earth's interior is But recently scientists began wondering if these facts hot -very hot -it is not fluid. interior was in a molten While boring the famous Simplon tunnel, many hun- really proved that the earth's unbearable state. And the more they wondered the more they dred feet above sea level, the heat became i For one thing they said: If the earth's in- and artificial cooling became necessary. Recent tests learned. the rock could terior is really in a molten state, liquid in other words, showed that the radium contents of why does not this molten mass rise and fall with the easily produce this great heat. 'ward. it would do were it liquid or The solution of the earth's heat, then, doubtless is tides which undoubtedly H. GERNSBACK. even plastic. Accurate measurements, however, show radium. p un , Ilpnnqll IIII U! ul un, u I,I,I,I,I IIIIII Illi\.IIIIIIh d iluI I IIÌiïll llllllllll I1III+ Ihugl =I: Vol. VII. Whole No. 84 Contents for April, 1920 No. 12 WATCHING PLANTS GROW Front Cover WEIGHING THE EARTH 1260 From a painting by Harold Brown By Louis E. Derr, Prof. of Physics, Mass. Inst. of Technology ELECTRIC POWER FROM THE SUN 1241 ELECTRIFYING CANAL BOATS AND BARGES 1262 BATTLE TRACER. 1242 By Robert G. Skerrett HEAT OF BODY DETECTED. 600 FEET AWAY 1244 TALKING OVER A SUNBEAM 1263 ONE MAN SUBWAY TRAIN 1245 By Prof. A. O. Rankine. Written especially for the ELECTRICAL WATCHING PLANTS GROW 1246 EXPERIMENTER. By a remarkably sensitive instrument devised by Sir Jagadis Bose, "AUTOMOBILE NEWS" 1265 of India POPULAR ASTRONOMY - OBSERVING THE HEAVENLY HELLO MARS! 1243 BODIES 1266 By H. Winfield Secor, Assoc. Member Amer. Inst. Electrical En- By Isabel M. Lewis, M. A., of the U. S. Naval Observatory gineers. "RABBIT CONTEST" AWARDS 1269 ELECTRICITY FOILS GERMAN SEALS 1251 Concluded from the March number By Fred C. Kelly PRACTICAL CHEMICAL EXPERIMENTS 1270 THE PHYSIOPHONE 1252 By Prof. Floyd L. Darrow By H. Gernsback HOME-MADE 110 -VOLT, 60 CYCLE INDUCTION MOTOR 1272 ELECTRO- MEDICAL FRAUDS 1254 By H. H. Parker By Joseph H. Kraus 1274 1256 THE "FINER WORKINGS STATIC ELECTRICITY THE EDUCATED HARPOON . aper. By Frederick von Lichtenow By Charles S. Wolfe Seco ELECTRIC BACHELOR MAID 1257 STORAGE BATTERY REPAI G Purdy By Henry Klaus By Edna MOTORS AND TELEGRAPH, CABLE AND RADIO DISPATCHES 1258 ELECTRICAL MACHINIST -NO.