s present m the chasms and basins, but it accounted for only a small percentage of the total The charged zones had no influence on the l)ehavior of neutralized dust or sand moving over them hi fact the first few tenths of a millimeter of the dust oceans was neutralized by ultraviolet exposure Pdchtrd is generally given credit for discerning the mechanism responsible for the sound emitted by drum sand 7 The record is a bit fuzzy here, but the academic discussion of who should receive credit is of little ARRAKIS ATMOSPHERE 26 ARRAKIS ATMOSPHERE import and as Ghralic states, 'It is the advancement of our knowledge that counts '' The use of the terminology "drum sand" was unique to Arrakis, but sound-emitting sands have been found on many Neta type planets, particularly those of the C and SO to 60 sub-classifications Local nomenclature depends upon die nature of the sound emitted, natives almost invariably naming the sands after the tonal quality closest to that of an indigenous musical instrument Most musical sands produce a single tonal sound which decays exponentially with time after being stepped upon or otherwise impacted A second step produces a similar sound with similar monotomc decrease in intensity Drum sand, however, emits a series of low-frequency beats from a single step These beats do die oat exponentially, but the pulsating (drumming) character is quite distinctive It was knows long before Hohshas's time that four conditions are necessary for a sand to sing First, the sand grains must be of approximately equal size Second, the grains must be bonded together This bonding is most commonly produced by the chemical deposition of water-soluble salts on the gram surfaces Third, the packing density must be uniform Finally, the underlying bedrock must be essentially parallel to the sand surface Any impact produces vibrations, but when the above conditions are met this impulse can create resonance and a tone is produced The sand layer vibrates as a unit If the ratios of mean grain spacing to grain diameter and mean grain spacing to bed thickness fall within prescribed limits, the tone will be audible to human ears These several conditions are not normally met and thus singing sands are not particularly common But if these conditions are met men we have an excellent analog of a musical instrument, albeit without the marvelous tonal and expressive capabilities of true musical instruments (including the human voice) Pachtra recognized that under certain conditions the ratios noted above could have values that resulted in a pattern of constructive and destructive interference in the sound waves This would cause a pulsating sound from a single impact or step Pachtra was not only a masterful applied mathematician but also an excellent experimentalist He spent several years on Arrakis performing on site investigations in spite of the obvious dangers This combination of field experimental and theoretical research has endear