p&c.thunderhead-第12部分

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　〃Is　that　it？〃　Nora　stared　at　the　screen　in　disappointment。　This　was　the　last　thing　she'd　expected：　confusing　monochromatic　patterns　like　no　landscape　she　had　ever　seen。　
　〃It's　just　the　beginning。　The　Imager　takes　infrared　emissions　and　radiometry　into　account；　but　that　would　take　too　long　to　explain。　It　also　looks　at　the　earth　in　three　different　radar　bands　and　two　polarizations。　Each　color　represents　a　different　band　of　radar；　or　a　different　polarization。　I'm　going　to　paint　each　color　on　to　the　screen；　layering　one　on　top　of　the　other。　This'll　take　a　few　minutes。〃　
　〃And　then　we'll　be　able　to　see　the　road？〃　
　Holroyd　gave　her　an　amused　look。　〃If　only　it　were　that　simple。　We're　going　to　have　to　beat　the　shit　out　of　the　data　before　we　can　see　the　road。〃　He　pointed。　〃This　red　is　L…Band　radar。　It　has　a　wavelength　of　twenty…five　centimeters　and　can　penetrate　five　meters　of　dry　sand。　Next；　I'll　add　C…Band。〃　
　A　blue　color　scrolled　down。　
　〃This　C…Band　has　a　six…centimeter　wavelength；　and　it　can　penetrate　at　most　two　meters。　So　what　you　see　here　is　a　little　shallower。〃　More　key　taps。　〃And　here　goes　X…Band。　That's　three　centimeters。　Basically；　it　gives　you　the　surface　itself。〃　
　A　neon　green　color　rolled　down　the　screen。　
　〃I　don't　see　how　you　can　even　begin　to　figure　all　this　out；〃　said　Nora；　gazing　at　the　distorted　swaths　of　colors。　
　〃Now　I'm　going　to　paint　in　the　polarizations。　The　outgoing　radar　beam　is　polarized　either　horizontally　or　vertically。　Sometimes　you　send　down　a　beam　horizontally　polarized；　and　it　bounces　back　vertically　polarized。　That　usually　happens　when　the　beam　encounters　a　lot　of　vertical　tree　trunks。〃　
　Nora　watched　as　another　color　was　added　to　the　screen。　It　was　taking　longer　for　the　program　to　paint　the　image　on　the　screen；　obviously；　the　putational　problem　was　being　more　plex。　
　〃Looks　like　a　de　Kooning；〃　said　Nora。　
　〃A　what？〃　
　Nora　waved　her　hand。　〃Never　mind。〃　
　Holroyd　turned　back　to　the　screen。　〃What　we've　got　is　a　posite　image　of　the　ground；　from　the　surface　to　about　fifteen　feet　deep。　Now　it's　a　matter　of　canceling　out　some　of　the　wavelengths　and　multiplying　others。　This　is　where　the　real　artistry　es　in。〃　Nora　could　hear　a　touch　of　pride　in　his　voice。　
　He　began　typing　again；　more　quickly　this　time。　Nora　watched　as　a　new　window　opened　on　the　screen；　lines　of　puter　code　racing　as　routines　were　added　and　deleted。　The　remote　desert　vastness　was　suddenly　covered　by　a　thin　web　of　tracks。　
　〃My　God！〃　Nora　cried。　〃There　they　are！　I　had　no　idea　the　Anasazi…〃　
　〃Hold　on　a　minute；〃　interrupted　Holroyd。　〃Those　are　modern　trails。〃　
　〃But　this　area　isn't　supposed　to　have　any　roads。〃　
　Holroyd　shook　his　head。　〃Some　of　these　are　probably　wild　horse　trails；　deer　trails；　coyote　trails；　mountain　lion　trails；　maybe　even　four…wheel…drive　tracks。　There　was　some　prospecting　for　uranium　in　this　area　in　the　fifties。　Most　of　these　tracks　you　wouldn't　be　able　to　see　on　the　ground。〃　
　Nora　slumped　back　in　her　chair。　〃With　all　those　trails；　how　can　we　ever　find　the　Anasazi　one？〃　
　Holroyd　grinned。　〃Be　patient。　The　older　the　road；　the　deeper　it　tends　to　lie。　Very　old　roads　also　tend　to　spread　through　erosion　and　wind。　The　pebbles　ancient　travelers　turned　up　have　been　smoothed　over　time；　while　new　roads　are　covered　with　sharper　pebbles。　The　sharper　pebbles　backscatter　more　strongly　than　the　smooth　ones。〃　
　He　continued　to　type。　〃No　one　knows　why；　but　sometimes　dramatic　things　happen　if　you　multiply　the　values　of　two　wavelengths　together；　or　divide　them　by　each　other；　or　cube　one　and　take　the　square　root　of　another　and　subtract　the　cosine　of　your　mother's　age。〃　
　〃Doesn't　sound　very　scientific；〃　said　Nora。　
　Holroyd　grinned。　〃No；　but　it's　my　favorite　part。　When　data's　buried　as　deeply　as　this；　it　takes　real　intuition　and　creativity　to　tease　it　out。〃　
　He　worked　with　steady　determination。　Every　few　minutes　the　image　changed：　sometimes　dramatically；　sometimes　subtly。　Once　Nora　asked　a　question；　but　Holroyd　merely　shook　his　head；　brow　furrowed。　At　times；　all　the　roads　vanished；　Holroyd　would　curse；　type　a　flurry　of　mands；　and　the　roads　returned。　
　Time　crawled　by；　and　Holroyd　grew　increasingly　frustrated。　The　sweat　stood　out　on　his　brow；　and　his　hands　flew　across　the　keys；　hitting　them　with　greater　force。　Nora's　back　began　to　ache；　and　she　found　herself　shifting　constantly　in　the　cheap　chair；　trying　to　find　a　fortable　position。　
　At　last；　Holroyd　sat　back　with　a　muttered　curse。　〃I've　tried　all　the　methods；　all　the　tricks。　The　data　just　won't　put　out。〃　
　〃What　do　you　mean？〃　
　〃Either　I　get　a　million　roads　and　trails；　or　I　get　nothing。〃　He　got　up　and　went　to　the　refrigerator。　〃Beer？〃　
　〃Sure。〃　Nora　glanced　at　the　clock。　It　was　seven；　but　the　apartment　was　still　insufferably　hot。　
　Holroyd　sat　down　again；　passing　her　the　beer　and　propping　a　leg　up　on　the　puter　table。　A　knobby　ankle　protruded　from　below　the　cuff；　pale　and　hairless。　〃Is　there　anything　unusual　about　the　Anasazi　roads？　Something　that　might　differentiate　them　from　all　these　animal　trails　and　modern　stuff？〃　
　Nora　thought　for　a　moment；　then　shook　her　head。　
　〃What　were　the　roads　used　for？〃　
　〃Actually；　they　weren't　really　roads　at　all。〃　
　Holroyd　pulled　his　leg　from　the　table　and　sat　up。　〃What　do　you　mean？〃　
　〃They're　still　a　deep　archaeological　mystery。　The　Anasazi　didn't　know　about　the　wheel　and　they　didn't　have　any　beasts　of　burden。　They　had　no　use　for　a　road。　So　why　they　would　take　such　trouble　to　build　them　has　always　puzzled　archaeologists。〃　
　〃Go　on；〃　Holroyd　urged。　
　〃Whenever　archaeologists　don't　understand　something；　they　cop　out　by　saying　it　served　a　religious　purpose。　That's　what　they　say　about　the　roads。　They　think　they　might　have　been　spirit　pathways；　rather　than　roads　for　living　beings　to　travel　on。　Roads　to　guide　the　spirits　of　the　dead　back　to　the　underworld。〃　
　〃What　do　these　roads　look　like？〃　Holroyd　took　a　swig　of　beer。　
　〃Not　much　of　anything；〃　Nora　said。　〃In　fact；　they're　almost　impossible　to　see　from　the　ground。〃　
　Holroyd　looked　at　her　expectantly。　〃How　were　they　built？〃　
　〃The　roads　were　exactly　thirty　feet　wide；　surfaced　with　adobe。　On　the　Great　North　Road　it　appears　that　pots　were　deliberately　broken　on　the　road　surface　to　consecrate　it。　The　roads　were　dotted　with　shrines　called　herraduras；　but　we　have　no　idea…〃　
　〃Wait　a　minute；〃　Holroyd　interrupted。　〃You　said　they　were　surfaced　with　adobe。　What　exactly　is　adobe？〃　
　〃Mud；　basically。〃　
　〃Imported？〃　
　〃No；　usually　just　the　local　dirt　mixed　with　water；　puddled　and　plastered。〃　
　〃Too　bad。〃　The　excitement　left　Holroyd's　voice　as　quickly　as　it　came。　
　〃There's　not　much　else。　When　the　Great　North　Road　was　finally　abandoned　around　1250；　it　seems　to　have　been　ritually　closed。　The　Anasazi　piled　brush　on　the　road　and　set　it　on　fire。　They　also　burned　all　the　shrines　along　the　road。　And　they　burned　several　large　structures　too；　one　of　which　I　excavated　a　few　years　ago；　called　Burned　Jacal。　Seems　it　was　some　kind　of　lighthouse　or　signaling　structure。　God　knows　what　they　used　it　for。〃　
　Holroyd　sat　forward。　〃They　burned　brush　on　the　road？〃　
　〃The　Great　North　Road；　anyway。　Nobody　has　done　much　research　on　the　other　roads。〃　
　〃How　much　brush？〃　
　〃A　lot；〃　said　Nora。　〃We　found　large　swaths　of　charcoal。〃　
　Holroyd　slammed　down　the　beer；　swivelled　in　his　chair；　and　began　hitting　keys　once　again。　〃Charcoal…carbon…has　a　very　specific　radar　signature。　Even　tiny　amounts　of　it　absorb　radar。　It　has　an　almost　nonexistent　backscatter。〃　
　The　image　on　the　screen　began　to　shift。　〃So　what　we're　going　to　look　for；〃　he　murmured；　〃is　just　the　opposite　of　what　I've　been　searching　for　all　this　time。　Instead　of　looking　for　a　particular　reflection；　we're　going　to　look　for　a　shadow。　A　linear　hole　in　the　data。〃　He　punched　a　final　key。　
　Nora　watched　as　the　image　on　the　screen　disappeared。　And　then…as　a　new　image　scrolled　down　the　screen　with　maddening　slowness…she　saw　a　long；　faint；　sinuous　black　line　etch　itself　across　the　landscape：　broken　in　countless　spots；　yet　unmistakable。　
　〃There　it　is；〃　said　Holroyd　quietly；　sitting　back　and　looking　at　her；　his　face　shining　with　triumph。　
　〃That's　my　road　to　Quivira？〃　Nora　asked；　her　voic