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第7部分（第4页）

〃Sir；　you　are　in　very　good　health　for　your　age　and　lifestyle。〃

〃And　what　about　going　down　there？〃　Norman　asked；　half　hoping　he　wouldnt　be　able　to　go。

〃Down　there？　Ive　talked　with　Captain　Barnes。　Shouldnt　be　any　problem　at　all；　sir。　If　youll　just　e　this　way　to　the　briefing；　sir　。。。〃

The　others　were　sitting　around　in　the　briefing　room；　with　Styrofoam　cups　of　coffee。　Norman　felt　glad　to　see　them。　He　dropped　into　a　chair　next　to　Harry。　〃Jesus；　did　you　have　the　damn　physical？〃

〃Yeah；〃　he　said。　〃Had　it　yesterday。〃

〃They　stuck　me　in　the　leg　with　this　long　needle；〃　Norman　said。

〃Really？　They　didnt　do　that　to　me。〃

〃And　how　about　breathing　with　that　clip　on　your　nose？〃

〃I　didnt　do　that；　either；〃　Harry　said。　〃Sounds　like　you　got　some　special　treatment；　Norman。〃

Norman　was　thinking　the　same　thing；　and　he　didnt　like　the　implications。　He　felt　suddenly　tired。

〃All　right；　men；　weve　got　a　lot　to　cover　and　just　three　hours　to　do　it；〃　a　brisk　man　said；　turning　off　the　lights　as　he　came　into　the　room。　Norman　hadnt　even　gotten　a　good　look　at　him。　Now　it　was　just　a　voice　in　the　dark。　〃As　you　know；　Daltons　law　governs　partial　pressures　of　mixed　gases；　or；　as　represented　here　in　algebraic　form　。。。〃

The　first　of　the　graphs　flashed　up。

PPa　=　Ptot　x　％　Vola

＇＇44＇＇　〃Now　lets　review　how　calculation　of　the　partial　pressure　might　be　done　in　atmospheres　absolute；　which　is　the　most　mon　procedure　we　employ…〃

The　words　were　meaningless　to　Norman。　He　tried　to　pay　attention；　but　as　the　graphs　continued　and　the　voice　droned　on；　his　eyes　grew　heavier　and　he　fell　asleep。

〃…be　taken　down　in　the　submarine　and　once　in　the　habitat　module　you　will　be　pressurized　to　thirty…three　atmospheres。　At　that　time　you　will　be　switched　over　to　mixed　gases；　since　it　is　not　possible　to　breathe　Earth　atmosphere　beyond　eighteen　atmospheres…〃

Norman　stopped　listening。　These　technical　details　only　filled　him　with　dread。　He　went　back　to　sleep；　awakening　only　intermittently。

〃…since　oxygen　toxicity　only　occurs　when　the　PO2　exceeds　point　7　ATA　for　prolonged　periods…

〃…nitrogen　narcosis；　in　which　nitrogen　behaves　like　an　anesthetic；　will　occur　in　mixed…gas　atmospheres　if　partial　pressures　exceeds　1。5　ATA　in　the　DDS…

〃…demand　open　circuit　is　generally　preferable；　but　you　will　be　using　semiclosed　circuit　with　inspired　fluctuations　of　608　to　760　millimeters…〃

He　went　back　to　sleep。

When　it　was　over；　they　walked　back　to　their　rooms。　〃Did　I　miss　anything？〃　Norman　said。

〃Not　really。〃　Harry　shrugged。　〃Just　a　lot　of　physics。〃

In　his　tiny　gray　room；　Norman　got　into　bed。　The　glowing　wall　clock　said　2300。　It　took　him　a　while　to　figure　out　that　that　was　11：00　p。m。　In　nine　more　hours；　he　thought；　I　will　begin　the　descent。

Then　he　slept。

THE　DEEP

DESCENT

In　the　morning　light；　the　submarine　Charon　V　bobbed　on　the　surface；　riding　on　a　pontoon　platform。　Bright　yellow；　it　looked　like　a　childs　bathtub　toy　sitting　on　a　deck　of　oildrums。

A　rubber　Zodiac　launch　took　Norman　over；　and　he　climbed　onto　the　platform；　shook　hands　with　the　pilot；　who　could　not　have　been　more　than　eighteen；　younger　than　his　son；　Tim。

〃Re