Back to the Moon with Nuclear Rockets

LettersCusa's TorquetumTo the Editor:It was a delight to see the astronomicalinstrument of Nicholas of Cusa, thetorquetum, c. 1444, the oldest in Europe,in its earlier version, as designedby Eratosthenes and used by the navigatorMaui on a voyage to circumnavigatethe Earth in 232 B.C. (Maui's Tanawa: ATorquetum of 232 B.C.," by Dr. SentielRommel, Spring 1999, p. 75.)Cusa designed his torquetum with thehelp of Regiomontanus, and it was corisideredto be too heavy and clumsy foruse. Eratosthenes' design is moreportable, and has a sundial time-pieceon the ring, which is in the plane of theecliptic.The best feature of this instrument isthat it can mechanically transfer coordinanceamong three coordinate systems:the direction of a star or planet incelestial latitude or longitude in refer-Cusa's torquetum, c. 1444, courtesy ofSt. Nikolaus Hospital, Cusanus Stift,founded 1458 (D-54470 Bernkastel-Kues, Germany).Let us agree that a risk does not existuntil it is well established with solid experimentalevidence. There is no nvidenceto show a risk from low dose orlow dose rate whole body radiation fordoses less than of 0.2 Cy (20 rads) ac uteor a much higher dose if spread overmonths or years. It is a rare dose that exceedsthese values.Pradel, unfortunately, accepts an assumptionas a fact. The InternationalCommission for Radiological Protec ion(ICRP) in 1977 made the simplifying assumptionthat radiation may be care nogenicdown to zero dose. This is the linenceto the plane of the ecliptic; rij htascensionand declination in the pi meof the equator; and, finally, the localcoordinates of horizon and height (hatis, azimuth N, S, E, W, and altitude ofan object).The torquetum is also said to be v; Liuablebecause it allows you to exarr inethe shift in the precession of :heequinoxes (50.25 seconds of arc Deryear, or 1 degree every 70 year;). Iwould like to know more about t lis.Also, the torquetum's companion insrumentis the astrolabe. Will 21st Cen uryalso publish something on the astrol ibesaid to be used by Maui?Eli Santi igoRidgefield Park, sl.J.The Editor RepliesYes, we intend to continue coverageof the ancient astronomy in future issues.Thanks for theSpring Issue!To the Editor:Just a few lines to say that the Spi ing1999 issue is outstanding. The "Discovery"articles and "Electric Embryo" wereexciting to read and bring into perse nalawareness. I've never found a dull is: ue,but this is the first that compels mn tosend along acknowledgement ,:ndthanks.Stanley VlantesMilford, Cc nn.A Response to Pradel onSimplifying Radiation Riskear, no-threshold (LNT) model of radiationrisk. In 1974, solid data contradictedthis model. Frigerio (1974) andEvans (1 974) present data that contradictthe LNT model. ( disagree withPradel's statement that "Epidemiologicalstudies will never be able to prove thatthese cancers [at low doses] do, or donot exist. . . ."Pradel does make some points in hisarticle, but I doubt if many readers willrecognize their simplicity. Equating asmall exposure from uranium processingto the increased dose from cosmicrays a few meters above our normal livinglevel, or breathing outdoor airrather than indoor air, with its higherradon level, is not an obvious simplification.I object to Pradel's analogy on twogrounds. First, it implicitly suggests thatsuch trifling doses really do have risks,and second, because the cosmic raysand radon level vary considerably withtime and place.Because a large fraction of your readersfly in jet planes, it would be useful topoint out that their dose from cosmicrays increases about a factor of 30 in goingfrom sea level to cruising altitude atabout 40,000 ft. My geiger counter typicallyhas a count rate of about 10 countsper min (cpm) at the airport, and about300 cpm at the cruising altitude. This isusually quite impressive to persons sittingnext to me, and also to the flight attendants.There is no evidence that anincrease of this amount has any negativehealth effects.Using an increase of radon level as arisk factor is contradicted by Cohen'sdata (1995) on radon level vs. lung cancerdeath rate. I doubt if any person, scientificallytrained or not, would look atCohen's data and decide that reducingyour radon level decreases your risk.His data indicate that U.S. counties withradon levels above 5 pCi/l have 40 percentlower lung cancer death rate thanthe counties with radon levels below0.5 pCi/l. This suggests that radon progenyin the lungs in some way reducesthe risk of a smoker dying from lungcancer.I suggest that the way to simplify radiationto the public is:(1) Do not mention risk for doses lessthan 0.2 Gy (20 rads), because there isno evidence that a risk exists.Continued on page 86LETTERS21stCENTlRY Summer 1999