Correspondence: Tesla Answers Mr. Manierre On Moon's Rotation

Sunday, February 23, 1919
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The New York Tribune February 23, 1919 Correspondence Tesla anewere Mr. Manierre and further explains the axial rotation of the moon IR: In your artlcls of February 2 Mr. Charles E. Msnlerre, commentlng upon my artlclo ln "The Electrlcnl Expcrlrnenter” for' February, whlch ap- peared ln The Trlbune of January 26, sug- gests that I glve a dellnltlon of axlal rota- tlon. I lntanded to he expllclt on thla polnt, as may be judged from the followlng quo- tatlon: “The unfalllng test of the spln- nlng ol a moss ls, however, the exlstence of energy of motlen. The moon ls not possessed of auch vlb vlvu." By thla I meant that "axial ra'tutlon" ls not slmply ‘rc-tatlon upon an axle” as nonehalantly do- llned ln dletlonarles, but ls u circular mo- tlon ln the true physical sense-that la, one ln whlch half the product ol the mass wlth the square of velocity ls a dellnlts and posftlva quantity. The mean ls a nearly apherlcal body, oi a radlus of about 1,081.5 mlles, from whleh I calculate lts volume to be approxlmatoly l,800,2l6fB00 euhla mllss. Blnce lta mean denslty ls 8.27, one eublo feet olmaterlsl composing lt welghs close to 208 pounds. Aceordlngly, the total wslght ol the aatel- llte ls about 70,0dll,000,000,000,000,000 and lta mass 2,488.lS00,000,U00,000,000 turrestrlal short tons. Assuming that the moon does physleally rotate upon lts axls, lt performs one revolutlon ln 27 days 'I hours 45 mln utes and 11 seconds, or 2,360,501 seconds If ln conformlty with mathematical prln clplss, we lmaglne the entlre mass concon ’trated at a dlatance from the centre equal to two-llfths of the radlus, then the calcu lated rotational veloclty ls 8.04 feet per second at whleh the globe would contalu energypsulllclant to run I 000,000 000 horse dewer for a perlod of 1,323 years. Now, I sly that there ls not enough of that energy ln the moon to run a dsllcate watch In astronomleal trsatlsas usually the ar gumelt§,ls advanced that lf the lunar globe dld not turn upon lta axle lt would expose 11,d'N,000,000,000,000,000 short foot ton. er all parts te ter-reitrlal view. As only a llttle over one-hal! ls vlslble lt must ro- tate.” But thls Inference ls erroneous, for lt only admlts of one alternatlve. There are an lnflnlte number ol axes besides lts own on each of whleh the moon might turn and stlll exhlhlt the aarus pocullarlty; I have etated ln my article that tha moon rotates about an axls, passlng through the centre of the earth, whlob ls not ltrlctly trud but does not vltlate the conclunlons I have drawn. It ls well known, of course, that? the‘two bedles revolve around \s corn- monn centre ol g-ravlty which ls at a_dls- tancn ol a llttle over 2,890 mlles from the esrth’s centre. Another mlstake ln hooks on astronomy ls mada ln conslderln: thls motlon edulvalent to that of a welgiht whlrled on a stnlng or In at sllng. In e flrst place, there is an essentlsl difference between these two de- vlcea though lnvolvlng the same mechanical prlnolpla. Il' n metal ball attached `to a string ls whirled around and the latter breaks an axfsl rotatlon ol the mlulle re- sults whlch ls dednltsly related ln magni- tude and dlrectlon to the motlon preeedlng.. By wey ol llluatratlonz If the-hall ,ls whlrle'd on the strlng eloelrwlse, ten times a secoudnthen when lt illee of( lt wlll rotau en lta axle twpnty tlrnes a recond, llkswlse ln the dlreotlon of a clock. Quite dlthrsat are the condltlens when the ball ls thrown from a sllng. In thls _ease a much more rsplfrotetlon le imparted to lt ln the opposlte sense. -There ls no #rue analogy to these la the motlaa ot the moon; It the grsvltetlenal strlsg. as lt were, would snap. the satellite would go-of! ln na tangent without the sllghtest swervlng or rotatlon, for there ls no momentum about the axls and, consequently, no tendency whatever to splnnlng motlon. Mr. Manlerra ls mistaken ln hls aurmlae as to what would happen ll the earth were suddenly ellmluated. Let ua suppose that thls would occur at the lustant when the moon ls lnopposltlan. Then lt would con- tlnue on lta elllptlcal path around the sua, presenting to lt steadlly the face whlcl: was always exposed to the earth. If, on the other hand, the latter would dlsappear at the moment ol eonjunctlon. the moon would gradyally swlug around through 180 de- gree! end, after a number of osclllatlons, revolve agaln with the same (he to the sun. ln elther ease there would he no perledls ehsnges, but.eternal day and night, respeeg. lvely, on the sldea turned toward, and away from the lomlllln-:Nl-'ROLL TIILL