,transcrib]'s notes3 ,! text ( ?is book has be5 pres]v$ 9 its orig9al =m ap>t f correction ( two typographic errors3 emb>rasm5t emb>rassm5t1 ,cassegranian ,cassegra9ian4 ,inconsi/5t hyph5ation has n be5 alt]$4 ,a l5g?y prelim9>y section conc]n+ ! ,smi?sonian ,in/itution prec$es ! actual subject matt]4 ,,smi?sonian ,,contributions ,,to ,,k4 ,,vol4 ,,xiv4 ,illu/ration ,,e ,,man ,,is ,a ,,valuable ,,memb] ,,( ,,society1 ,,:o1 ,,by ,,8 ,,obs]vations1 ,,rese>*es1 ,,& ,,exp]im5ts1 ,,procures ,,k ,,= ,,m54--,,smi?son4 ,,city ,,( ,,wa%+ton3 ,,publi%$ ,,by ,,! ,,smi?sonian ,,in/itution4 ,,mdccclxv4 ,,adv]tisem5t4 ,?is volume =ms ! f\rte5? ( a s]ies1 compos$ ( orig9al memoirs on diff]5t bran*es ( k1 publi%$ at ! exp5se1 & "u ! direction1 ( ! ,smi?sonian ,in/itution4 ,! publication ( ?is s]ies =ms "p ( a g5]al plan adopt$ = c>ry+ into effect ! b5evol5t int5tions ( ,,james ,,smi?son1 ,esq41 ( ,engl&4 ,?is g5tleman left 8 prop]ty 9 tru/ to ! ,unit$ ,/ates ( ,am]ica1 to f\nd1 at ,wa%+ton1 an in/itution :i* %\ld be> 8 own "n1 & h = its objects ! 8increase & diffusion ( k among m540 ,?is tru/ 0 accept$ by ! ,gov]nm5t ( ! ,unit$ ,/ates1 & an ,act ( ,congress 0 pass$ ,augu/ #aj1 #ahdf1 con/itut+ ! ,presid5t & ! o!r pr9cipal executive (fic]s ( ! g5]al gov]nm5t1 ! ,*ief ,ju/ice ( ! ,supreme ,c\rt1 ! ,mayor ( ,wa%+ton1 & su* o!r p]sons z !y might elect honor>y memb]s1 an e/abli%m5t "u ! "n ( ! 8,,smi?sonian ,,in/itution ,,= ,,! ,,increase ,,& ,,diffusion ,,( ,,k ,,among ,,m540 ,! memb]s & honor>y memb]s ( ?is e/abli%m5t are to hold /at$ & special meet+s = ! sup]vision ( ! affairs ( ! ,in/itution1 & = ! advice & in/ruction ( a ,bo>d ( ,reg5ts1 to :om ! f9ancial & o!r affairs are intru/$4 ,! ,bo>d ( ,reg5ts consi/s ( ?ree memb]s ex (ficio ( ! e/abli%m5t1 namely1 ! ,vice-,presid5t ( ! ,unit$ ,/ates1 ! ,*ief ,ju/ice ( ! ,supreme ,c\rt1 & ! ,mayor ( ,wa%+ton1 toge!r ) twelve o!r memb]s1 ?ree ( :om are appo9t$ by ! ,s5ate f its own body1 ?ree by ! ,h\se ( ,repres5tatives f its memb]s1 & six p]sons appo9t$ by a jo9t resolution ( bo? h\ses4 ,to ?is ,bo>d is giv5 ! p[] ( elect+ a ,secret>y & o!r (fic]s1 = conduct+ ! active op]ations ( ! ,in/itution4 ,to c>ry into effect ! purposes ( ! te/ator1 ! plan ( organization %\ld evid5tly embrace two objects3 "o1 ! increase ( k by ! addition ( new tru?s to ! exi/+ /ock2 ! o!r1 ! diffusion ( k1 ?us increas$1 among m54 ,no re/riction is made 9 favor ( any k9d ( k2 &1 h5ce1 ea* bran* is entitl$ to1 & %\ld receive1 a %>e ( att5tion4 ,! ,act ( ,congress1 e/abli%+ ! ,in/itution1 directs1 z a "p ( ! plan ( organization1 ! =mation ( a ,libr>y1 a ,museum1 & a ,gall]y ( ,art1 toge!r ) provisions = physical rese>* & popul> lectures1 :ile x leaves to ! ,reg5ts ! p[] ( adopt+ su* o!r p>ts ( an organization z !y may deem be/ suit$ to promote ! objects ( ! beque/4 ,aft] mu* delib]ation1 ! ,reg5ts resolv$ to divide ! annual income into two p>ts--"o "p to be devot$ to ! increase & diffusion ( k by means ( orig9al rese>* & publications--! o!r "p ( ! income to be appli$ 9 accordance ) ! requirem5ts ( ! ,act ( ,congress1 to ! gradual =mation ( a ,libr>y1 a ,museum1 & a ,gall]y ( ,art4 ,! foll[+ are ! details ( ! p>ts ( ! g5]al plan ( organization provisionally adopt$ at ! meet+ ( ! ,reg5ts1 ,dec4 #h1 #ahdg4 ,,details ,,( ,,! ,,fir/ ,,"p ,,( ,,! ,,plan4 ,i4 ,,to ,,increase ,,k4--,x is propos$ to /imulate rese>*1 by (f]+ rew>ds = orig9al memoirs on all subjects ( inve/igation4 #a4 ,! memoirs ?us obta9$1 to be publi%$ 9 a s]ies ( volumes1 9 a qu>to =m1 & entitl$ 8,smi?sonian ,contributions to ,k40 #b4 ,no memoir1 on subjects ( physical sci5ce1 to be accept$ = publication1 :i* does n furni% a positive addition to human k1 re/+ on orig9al rese>*2 & all unv]ifi$ speculations to be reject$4 #c4 ,ea* memoir pres5t$ to ! ,in/itution1 to be submitt$ = exam9ation to a commission ( p]sons ( reputation = le>n+ 9 ! bran* to :i* ! memoir p]ta9s2 & to be accept$ = publication only 9 case ! report ( ?is commission is favorable4 #d4 ,! commission to be *os5 by ! (fic]s ( ! ,in/itution1 & ! "n ( ! au?or1 z f> z practicable1 conceal$1 unless a favorable decision be made4 #e4 ,! volumes ( ! memoirs to be ex*ang$ = ! ,transactions ( lit]>y & sci5tific societies1 & copies to be giv5 to all ! colleges1 & pr9cipal libr>ies1 9 ?is c\ntry4 ,"o "p ( ! rema9+ copies may be (f]$ = sale2 & ! o!r c>efully pres]v$1 to =m complete sets ( ! "w1 to supply ! dem& f new in/itutions4 #f4 ,an ab/ract1 or popul> acc\nt1 ( ! cont5ts ( ^! memoirs to be giv5 to ! public1 ?r\gh ! annual report ( ! ,reg5ts to ,congress4 ,,ii4 ,,to ,,increase ,,k4--,x is also propos$ to appropriate a portion ( ! income1 annually1 to special objects ( rese>*1 "u ! direction ( suitable p]sons4 #a4 ,! objects1 & ! am\nt appropriat$1 to be recomm5d$ by c\nsellors ( ! ,in/itution4 #b4 ,appropriations 9 diff]5t ye>s to diff]5t objects2 s t1 9 c\rse ( "t1 ea* bran* ( k may receive a %>e4 #c4 ,! results obta9$ f ^! appropriations to be publi%$1 ) ! memoirs be=e m5tion$1 9 ! volumes ( ! ,smi?sonian ,contributions to ,k4 #d4 ,examples ( objects = :i* appropriations may be made3-- 7#a47 ,sy/em ( ext5d$ meteorological obs]vations = solv+ ! problem ( ,am]ican /orms4 7#b47 ,explorations 9 descriptive natural hi/ory1 & geological1 ma!matical1 & topographical surveys1 to collect mat]ial = ! =mation ( a ,physical ,atlas ( ! ,unit$ ,/ates4 7#c47 ,solution ( exp]im5tal problems1 su* z a new det]m9ation ( ! weight ( ! e>?1 ( ! velocity ( electricity1 & ( light2 *emical analyses ( soils & plants2 collection & publication ( articles ( sci5ce1 accumulat$ 9 ! (fices ( ,gov]nm5t4 7#d47 ,in/itution ( /ati/ical inquiries ) ref]5ce to physical1 moral1 & political subjects4 7#e47 ,hi/orical rese>*es1 & accurate surveys ( places celebrat$ 9 ,am]ican hi/ory4 7#f47 ,e?nological rese>*es1 p>ticul>ly ) ref]5ce to ! diff]5t races ( m5 9 ,nor? ,am]ica2 also explorations1 & accurate surveys1 ( ! m\nds & o!r rema9s ( ! anci5t p ( our c\ntry4 ,i4 ,,to ,,diffuse ,,k4--,x is propos$ to publi% a s]ies ( reports1 giv+ an acc\nt ( ! new discov]ies 9 sci5ce1 & ( ! *anges made f ye> to ye> 9 all bran*es ( k n /rictly pr(essional4 #a4 ,"s ( ^! reports may be publi%$ annually1 o!rs at long] int]vals1 z ! income ( ! ,in/itution or ! *anges 9 ! bran*es ( k may indicate4 #b4 ,! reports are to be prep>$ by collaborators1 em95t 9 ! diff]5t bran*es ( k4 #c4 ,ea* collaborator to be furni%$ ) ! j\rnals & publications1 dome/ic & =eign1 necess>y to ! compilation ( 8 report2 to be paid a c]ta9 sum = 8 labors1 & to be nam$ on ! title-page ( ! report4 #d4 ,! reports to be publi%$ 9 sep>ate p>ts1 s t p]sons int]e/$ 9 a p>ticul> bran*1 c procure ! p>ts relat+ to x1 )\t pur*as+ ! :ole4 #e4 ,^! reports may be pres5t$ to ,congress1 = p>tial di/ribution1 ! rema9+ copies to be giv5 to lit]>y & sci5tific in/itutions1 & sold to individuals = a mod]ate price4 ,! foll[+ are "s ( ! subjects :i* may be embrac$ 9 ! reports3-- ,i4 ,,physical ,,class4 #a4 ,physics1 includ+ a/ronomy1 natural philosophy1 *emi/ry1 & meteorology4 #b4 ,natural hi/ory1 includ+ botany1 zoology1 geology1 c4 #c4 ,agriculture4 #d4 ,application ( sci5ce to arts4 ,,ii4 ,,moral ,,& ,,political ,,class4 #e4 ,e?nology1 includ+ p>ticul> hi/ory1 comp>ative philology1 antiquities1 c4 #f4 ,/ati/ics & political economy4 #g4 ,m5tal & moral philosophy4 #h4 ,a survey ( ! political ev5ts ( ! _w2 p5al re=m1 c4 ,,iii4 ,,lit]ature ,,& ,,! ,,f9e ,,arts4 #i4 ,mod]n lit]ature4 #aj4 ,! f9e arts1 & _! application to ! useful arts4 #aa4 ,bibliography4 #ab4 ,obitu>y notices ( di/+ui%$ individuals4 ,,ii4 ,,to ,,diffuse ,,k4--,x is propos$ to publi% occasionally sep>ate treatises on subjects ( g5]al int]e/4 #a4 ,^! treatises may occasionally consi/ ( valuable memoirs translat$ f =eign languages1 or ( articles prep>$ "u ! direction ( ! ,in/itution1 or procur$ by (f]+ premiums = ! be/ exposition ( a giv5 subject4 #b4 ,! treatises to be submitt$ to a commission ( compet5t judges1 previ\s to _! publication4 ,,details ,,( ,,! ,,second ,,"p ,,( ,,! ,,plan ,,( ,,organization4 ,?is "p contemplates ! =mation ( a ,libr>y1 a ,museum1 & a ,gall]y ( ,art4 #a4 ,to c>ry out ! plan be=e describ$1 a libr>y w be requir$1 consi/+1 #a/1 ( a complete collection ( ! transactions & proce$+s ( all ! le>n$ societies ( ! _w2 #b;d1 ( ! m important curr5t p]iodical publications1 & o!r works necess>y 9 prep>+ ! p]iodical reports4 #b4 ,! ,in/itution %\ld make special collections1 p>ticul>ly ( objects to v]ify its own publications4 ,also a collection ( in/rum5ts ( rese>* 9 all bran*es ( exp]im5tal sci5ce4 #c4 ,) ref]5ce to ! collection ( books1 o!r ?an ^? m5tion$ above1 catalogues ( all ! diff]5t libr>ies 9 ! ,unit$ ,/ates %\ld be procur$1 9 ord] t ! valuable books fir/ pur*as$ may be su* z are n to be f\nd else:]e 9 ! ,unit$ ,/ates4 #d4 ,also catalogues ( memoirs1 & ( books 9 =eign libr>ies1 & o!r mat]ials1 %\ld be collect$1 = r5d]+ ! ,in/itution a c5tre ( bibliographical k1 :5ce ! /ud5t may be direct$ to any "w :i* he may require4 #e4 ,x is believ$ t ! collections 9 natural hi/ory w increase by donation1 z rapidly z ! income ( ! ,in/itution c make provision = _! reception2 &1 !re=e1 x w seldom be necess>y to pur*ase any article ( ?is k9d4 #f4 ,attempts %\ld be made to procure = ! gall]y ( art1 ca/s ( ! mo/ celebrat$ articles ( anci5t & mod]n sculpture4 #g4 ,! arts may be enc\rag$ by provid+ a room1 free ( exp5se1 = ! exhibition ( ! objects ( ! ,art-,union1 & o!r simil> societies4 #h4 ,a small appropriation %\ld annually be made = models ( antiquity1 su* z ^? ( ! rema9s ( anci5t temples1 c4 #i4 ,! ,secret>y & 8 assi/ants1 dur+ ! session ( ,congress1 w be requir$ to illu/rate new discov]ies 9 sci5ce1 & to exhibit new objects ( art2 di/+ui%$ individuals %\ld also be invit$ to give lectures on subjects ( g5]al int]e/4 99 99 99 99 99 ,9 accordance ) ! rules adopt$ 9 ! programme ( organization1 ea* memoir 9 ?is volume has be5 favorably report$ on by a ,commission appo9t$ = its exam9ation4 ,x is h[ev] impossible1 9 mo/ cases1 to v]ify ! /atem5ts ( an au?or2 &1 !re=e1 nei!r ! ,commission nor ! ,in/itution c be responsible = m ?an ! g5]al "* ( a memoir4 99 99 99 99 99 ,! foll[+ rules h be5 adopt$ = ! di/ribution ( ! qu>to volumes ( ! ,smi?sonian ,contributions3-- #a4 ,!y are to be pres5t$ to all le>n$ societies :i* publi% ,transactions1 & give copies ( ^!1 9 ex*ange1 to ! ,in/itution4 #b4 ,also1 to all =eign libr>ies ( ! fir/ class1 provid$ !y give 9 ex*ange _! catalogues or o!r publications1 or an equival5t f _! duplicate volumes4 #c4 ,to all ! colleges 9 actual op]ation 9 ?is c\ntry1 provid$ !y furni%1 9 return1 meteorological obs]vations1 catalogues ( _! libr>ies & ( _! /ud5ts1 & all o!r publications issu$ by !m relative to _! organization & hi/ory4 #d4 ,to all ,/ates & ,t]ritories1 provid$ !re be giv51 9 return1 copies ( all docum5ts publi%$ "u _! au?ority4 #e4 ,to all incorporat$ public libr>ies 9 ?is c\nty1 n includ$ 9 any ( ! =ego+ classes1 n[ conta9+ m ?an #aj1jjj volumes2 & to small] libr>ies1 :]e a :ole ,/ate or l>ge di/rict w\ld be o!rwise unsuppli$4 ,,(fic]s ,,( ,,! ,,smi?sonian ,,in/itution4 ,,! ,,presid5t ,,( ,,! ,,unit$ ,,/ates1 ,ex-(ficio ,,presid+ ,,(fic] ,,( ,,! ,,in/itution4 ,,! ,,vice-,,presid5t ,,( ,,! ,,unit$ ,,/ates1 ,ex (ficio ,,second ,,presid+ ,,(fic]4 ,,salmon ,p4 ,,*ase1 ,,*ancellor ,,( ,,! ,,in/itution4 ,,joseph ,,h5ry1 ,,secret>y ,,( ,,! ,,in/itution4 ,,sp5c] ,f4 ,,baird1 ,,assi/ant ,,secret>y4 ,w4 ,w4 ,,seaton1 ,,treasur]4 ,,alex&] ,d4 ,,ba*e1 ,,ri*>d ,,walla*1 ,,executive ,,committee4 ,,ri*>d ,,delafield1 ,,reg5ts4 ---- ---- ,vice-,presid5t ( ! ,unit$ ,/ates4 ,,salmon ,p4 ,,*ase1 ,*ief ,ju/ice ( ! ,unit$ ,/ates4 ,,ri*>d ,,walla*1 ,mayor ( ! ,city ( ,wa%+ton4 ,,lyman ,,trumbull1 ,memb] ( ! ,s5ate ( ! ,unit$ ,/ates4 ,,william ,p4 ,,fess5d51 ,,g>rett ,,davis1 ,,samuel ,s4 ,,cox1 ,memb] ( ! ,h\se ( ,repres5tatives ,u4 ,s4 ,,james ,w4 ,,patt]son1 ,,h5ry ,w4 ,,davis1 ,,william ,b4 ,,a/or1 ,citiz5 ( ,new ,york4 ,,!odore ,d4 ,,woolsey1 ( ,connecticut4 ,,l\is ,,agassiz1 ( ,massa*usetts4 7,vacancy47 ---- ---- ,,alex&] ,d4 ,,ba*e1 ( ,wa%+ton4 ,,ri*>d ,,delafield1 ( ,wa%+ton4 ,,memb]s ,,ex-,,(ficio ,,( ,,! ,,in/itution4 ,,&rew ,,johnson1 ,presid5t ( ! ,unit$ ,/ates4 ---- ---- ,vice-,presid5t ( ! ,unit$ ,/ates4 ,,william ,h4 ,,sew>d1 ,secret>y ( ,/ate4 ,,hugh ,,mccullo*1 ,secret>y ( ! ,treasury4 ,,edw9 ,m4 ,,/anton1 ,secret>y ( ,w>4 ,,gideon ,,welles1 ,secret>y ( ! ,navy4 ,,william ,,d5nison1 ,po/ma/]-,g5]al4 ,,james ,,spe$1 ,attorney-,g5]al4 ,,salmon ,p4 ,,*ase1 ,*ief ,ju/ice ( ! ,unit$ ,/ates4 ,,david ,p4 ,,holl[ay1 ,commission] ( ,pat5ts4 ,,ri*>d ,,walla*1 ,mayor ( ! ,city ( ,wa%+ton4 ,,honor>y ,,memb]4 ,,james ,,h>lan4 ,! ,secret>y ( ! ,int]ior4 ,,table ,,( ,,cont5ts4#a #a ,ea* memoir is sep>ately pag$ & index$4 ,,page ,,article ,i4 ,,introduction4 ,pp4 #af4 ,adv]tisem5t iii ,li/ ( ,(fic]s ( ! ,smi?sonian ,in/itution ix ,,article ,,ii4 ,,discussion ,,( ,,! ,,magnetic ,,& ,,meteorological ,,obs]vations ,,made ,,at ,,! ,,gir>d ,,college ,,obs]vatory1 ,,philadelphia1 ,,9 #ahdj1 #ahda1 #ahdb1 #ahdc1 #ahdd1 ,,& #ahde4 ,?ird ,section1 compris+ ,p>ts ,,vii1 ,,viii1 ,,& ,,ix4 ,,v]tical ,,=ce4 ,,inve/igation ,,( ,,! ,,elev5 7,,or ,,t57 ,,ye> ,,p]iod ,,& ,,( ,,! ,,di/urbances ,,( ,,! ,,v]tical ,,compon5t ,,( ,,! ,,magnetic ,,=ce1 ,,& ,,app5dix ,,on ,,! ,,magnetic ,,effect ,,( ,,! ,,aurora ,,borealis2 ,,) ,,an ,,inve/igation ,,( ,,! ,,sol> ,,diurnal ,,v>iation1 ,,& ,,( ,,! ,,annual ,,inequality ,,( ,,! ,,v]tical ,,=ce2 ,,& ,,( ,,! ,,lun> ,,effect ,,or ,,! ,,v]tical ,,=ce1 ,,! ,,incl9ation1 ,,& ,,total ,,=ce4 ,by ,a4 ,d4 ,,ba*e1 ,,ll4 ,d41 ,f4 ,r4 ,s41 ,mem4 ,corr4 ,acad4 ,sc4 ,p>is2 ,pre/4 ,nat4 ,acad4 ,sci5ces2 ,sup]9t5d5t ,u4 ,s4 ,coa/ ,survey4 ,pp4 #gb4 7,publi%$ ,may1 #ahfd47 ,,article ,,iii4 ,,discussion ,,( ,,! ,,magnetic ,,& ,,meteorological ,,obs]vations ,,made ,,at ,,! ,,gir>d ,,college ,,obs]vatory1 ,,philadelphia1 ,,9 #ahdj1 #ahda1 #ahdb1 #ahdc1 #ahdd1 ,,& #ahde4 ,f\r? ,section1 compris+ ,p>ts ,x1 ,,xi1 ,,& ,,xii4 ,,dip ,,& ,,total ,,=ce4 ,,analysis ,,( ,,! ,,di/urbances ,,( ,,! ,,dip ,,& ,,total ,,=ce2 ,,discussion ,,( ,,! ,,sol> ,,diurnal ,,v>iation ,,& ,,annual ,,inequality ,,( ,,! ,,dip ,,& ,,total ,,=ce2 ,,& ,,discussion ,,( ,,! ,,absolute ,,dip1 ,,) ,,! ,,f9al ,,values ,,= ,,decl9ation1 ,,dip ,,& ,,=ce ,,betwe5 #ahda ,,& #ahde4 ,by ,a4 ,d4 ,,ba*e1 ,,ll4 ,d41 ,f4 ,r4 ,s41 ,mem4 ,corr4 ,acad4 ,sc4 ,p>is2 ,pre/4 ,nat4 ,acad4 ,sci5ces2 ,sup]9t5d5t ,u4 ,s4 ,coa/ ,survey4 ,pp4 #dd4 7,publi%$ ,janu>y1 #ahfe47 ,,article ,,iv4 ,,on ,,! ,,con/ruction ,,( ,a ,,silv]$ ,,glass ,,telescope1 ,,fifte5 ,,& ,a ,,half ,,in*es ,,9 ,,ap]ture1 ,,& ,,its ,,use ,,9 ,,cele/ial ,,photography4 ,by ,,h5ry ,,drap]1 ,m4 ,d41 ,pr(essor ( ,natural ,sci5ce 9 ! ,univ]sity ( ,new ,york4 ,pp4 #fj4 7,publi%$ ,july1 #ahfd47 #a4 ,gr9d+ & ,poli%+ ! ,mirrors #b #b4 ,! ,telescope ,m\nt+ #bg #c4 ,! ,clock ,movem5t #ch #d4 ,! ,obs]vatory #da #e4 ,! ,photographic ,laboratory #df #f4 ,! ,photographic ,enl>g] #ea ,,article ,v4 ,,pal,,ontology ,,( ,,! ,,upp] ,,miss\ri3 ,a ,,report ,,^u ,,collections ,,made ,,pr9cipally ,,by ,,! ,,exp$itions ,,"u ,,comm& ,,( ,,lieut4 ,g4 ,k4 ,,w>r51 ,u4 ,s4 ,top4 ,engrs41 ,,9 #ahee ,,& #ahef4 ,,inv]tebrates4 ,by ,f4 ,b4 ,,meek ,,& ,f4 ,v4 ,,hayd51 ,m4 ,d4 ,"p ,i4 ,pp4 #aeh1 & five ,plates4 7,publi%$ ,april1 #ahfe47 ,introductory ,rem>ks vii ,i4 ,silurian ,age4 ,potsdam ,p]iod #a ,,ii4 ,c>bonif]\s ,age4 ,c>bonif]\s ,p]iod #aa ,,iii4 ,c>bonif]\s ,age4 ,p]mian ,p]iod #dh ,,iv4 ,reptilian ,age4 ,jurassic ,p]iod #ff ,index #aba ,explanations ( ,plates4 ,,article ,,vi4 ,,cretace\s ,,reptiles ,,( ,,! ,,unit$ ,,/ates4 ,by ,,joseph ,,leidy1 ,m4 ,d41 ,pr(essor ( ,anatomy 9 ! ,univ]sity ( ,p5nsylvania1 ,curator ( ! ,academy ( ,natural ,sci5ces ( ,philadelphia4 ,pp4 #adj & tw5ty plates4 7,publi%$ ,may1 #ahfe47 ,introduction #a ,sauria #e ,*elonia #ajd ,a ,synopsis1 9 :i* an attempt is made to def9e m closely ! ,g5]a & ,species ( ,reptiles ^: rema9s are describ$ 9 ! prec$+ pages #aae ,index #aba ,ref]5ces to ! ,plates #abc ,,smi?sonian ,,contributions ,,to ,,k4 ----#ahj---- ,,on ,,! ,,con/ruction ,,( ,a ,,silv]$ ,,glass ,,telescope1 ,,fifte5 ,,& ,a ,,half ,,in*es ,,9 ,,ap]ture1 ,,& ,,its ,,use ,,9 ,,cele/ial ,,photography4 ,,by ,,h5ry ,,drap]1 ,m4 ,d41 ,,pr(essor ,,( ,,natural ,,sci5ce ,,9 ,,! ,,univ]sity ,,( ,,new ,,york4 ,,accept$ ,,= ,,publication1 ,,janu>y1 #ahfd4 ,,commission ,,to ,,:i* ,,?is ,,pap] ,,has ,,be5 ,,ref]r$4 ,pr(4 ,,wolcott ,,gibbs4 ,com4 ,j4 ,m4 ,,gilliss1 ,u4 ,s4 ,n4 ,,joseph ,,h5ry1 ,secret>y ,s4 ,i4 ,,coll9s1 ,,pr9t]1 ,,philadelphia4 ,,cont5ts4 ,,hi/orical ,,sket* ,,( ,,! ,,telescope4 ,,memoir ,,divid$ ,,into ,,six ,,sections3-- #a4 ,,gr9d+ ,,& ,,poli%+ ,,! ,,mirrors #b #a4 ,exp]im5ts on a metal speculum4 ,corrosion by aqua regia2 voltaic gr9d+ #b #b4 ,silv]+ glass4 ,f\cault's & ,cimeg's processes2 details ( silv]+ a mirror2 ?ickness & durability ( silv] films2 _! use 9 dagu]reotyp+ #b #c4 ,gr9d+ & poli%+ glass4 ,division ( subject #f a4 ,peculi>ities ( glass2 effects ( pressure2 effects ( heat2 oblique mirrors #f b4 ,em]y & r\ge2 elutriation ( em]y #aj c4 ,tools ( iron1 lead1 pit*2 ! gauges2 ! lead5 tool2 ! iron tool2 ! pit* poli%] #aj d4 ,me?ods ( exam9ation2 two te/s1 eyepiece & opaque scre52 appe>ance ( sph]ical surface2 oblate sph]oidal surface2 hyp]bolic surface2 irregul> surface2 details ( te/s2 atmosph]ic movem5ts2 correction = p>allel rays by measure2 appe>ances 9 relief on mirrors #ac e4 ,ma*9es2 ,"l ,rosse2 ,mr4 ,lassell2 spiral /roke ma*9e2 its con/ruction & use2 ! foot-p[]2 me?od ( local corrections2 its advantages & disadvantages2 ma*9e = local corrections2 description & use #ai #d4 ,eyepieces1 plane mirrors1 & te/ objects #bf #b4 ,,! ,,telescope ,,m\nt+ #bg ,/ation>y eyepiece2 me?od ( c\nt]pois+ #bg a4 ,! tube2 ! mirror support2 air sac2 curr5ts 9 ! tube #bh b4 ,! support+ frame #ca #c4 ,,! ,,clock ,,movem5t #cc a4 ,! slid+ platehold]2 ! frictionless slide #cc b4 ,! clepsydra2 ! s&-clock #cf c4 ,! sun cam]a #dj #d4 ,,! ,,obs]vatory #da a4 ,! build+ #da b4 ,! dome2 its peculi>ities #dd c4 ,! obs]v]'s *air #de #e4 ,,! ,,photographic ,,laboratory #df a4 ,description ( ! ap>tm5t #df b4 ,photographic processes2 wa%$ plates2 difficulties ( cele/ial photography #dg #f4 ,,! ,,photographic ,,enl>g] #ea a4 ,l[ p[]s2 use ( a concave mirror1 its novelty & advantages2 ( ! mak+ ( rev]ses #ea b4 ,high p[]s2 microscopic photography #ed ,,an ,,acc\nt ,,( ,,! ,,con/ruction ,,& ,,use ,,( ,a ,,silv]$ ,,glass ,,telescope4 ,! con/ruction ( a reflect+ telescope capable ( %[+ e cele/ial object n[ kn[n1 is n a v difficult task4 ,x dem&s pr9cipally p]sev]ance & c>eful obs]vation ( m9uti4 ,! co/ ( mat]ials is b trifl+ comp>$ ) ! result obta9$1 & ,i c see no reason :y silv]$ glass in/rum5ts %\ld n come into g5]al use among amateurs4 ,! future hopes ( ,a/ronomy lie 9 ! multitude ( obs]v]s1 & 9 ! conc5tration ( ! action ( _m m9ds4 ,if :at is writt5 "h %\ld aid 9 ! advance ( t noble /udy1 ,i %all feel amply repaid = my labor4 ,a %ort hi/orical sket* ( ?is telescope may n be un9t]e/+4 ,9 ! summ] ( #aheg1 ,i visit$ ,"l ,rosse's great reflector1 at ,p>son/[n1 &1 9 addition to an inspection ( ! ma*9]y = gr9d+ & poli%+1 _h an opportunity ( see+ sev]al cele/ial objects ?r\gh x4 ,on return+ home1 9 #aheh1 ,i det]m9$ to con/ruct a simil>1 ?\gh small] in/rum5t2 :i*1 h[ev]1 %\ld be l>g] ?an any 9 ,am]ica1 & be especially adapt$ = photography4 ,accord+ly1 9 ,septemb] ( t ye>1 a #ae in* speculum 0 ca/1 & a ma*9e to "w x made4 ,9 #ahfj1 ! obs]vatory 0 built1 by ! village c>p5t]1 f my own designs1 at my fa!r's c\ntry seat1 & ! telescope ) its metal speculum m\nt$4 ,?is latt] 01 h[ev]1 soon aft] ab&on$1 & silv]$ glass adopt$4 ,dur+ #ahfa1 ! difficulties ( gr9d+ & poli%+ t are detail$ 9 ?is acc\nt 7 met )1 & ! rem$ies = _m ( !m asc]ta9$4 ,! exp]im5ts 7 conduct$ by ! aid ( ?ree #ae-a_/b in* disks ( glass1 toge!r ) a v>iety ( small] pieces4 ,?ree mirrors ( ! same focal l5g? & ap]ture are almo/ ess5tial1 = x n infrequ5tly happ5s t two 9 succession w be s simil>1 t a ?ird is requir$ = attempt+ an advance beyond !m4 ,"o ( ^! 0 made to acquire a p>abolic figure1 & bore a p[] ( #a1jjj4 ,! w9t] 0 devot$ to p]fect+ ! art ( silv]+1 & to ! /udy ( special photographic processes4 ,a l>ge portion ( #ahfb 0 sp5t ) a regim5t 9 a campaign 9 ,virg9ia1 & b few photographs 7 produc$ till autumn1 :5 s& clocks & clepsydras ( sev]al k9ds hav+ be5 made1 ! driv+ me*anism atta9$ great excell5ce4 ,dur+ ! w9t]1 ! art ( local corrections 0 acquir$1 & two #ae-a_/b in* mirrors1 z well z two ( #i in*es = ! photographic enl>g+ app>atus1 7 complet$4 ,! great] "p ( #ahfc has be5 occupi$ by lun> & planet>y photography1 & ! enl>gem5t ( ! small negatives obta9$ at ! focus ( ! great reflector4 ,lun> negatives h be5 produc$ :i* h be5 magnifi$ to #c feet 9 diamet]4 ,i h also f9i%$ two mirrors #ae-a_/b in*es 9 ap]ture1 suitable = a ,h]s*elian telescope1 t is1 :i* c only conv]ge oblique p5cils to a focus free f ab]ration4 ,?is "w has all be5 accompli%$ 9 ! int]vals ( pr(essional labor4 ,! details ( ! prec$+ op]ations are arrang$ z foll[s3 #a4 ,,gr9d+ ,,& ,,poli%+ ,,! ,,mirrors2 #b4 ,,! ,,telescope ,,m\nt+2 #c4 ,,! ,,clock ,,movem5t2 #d4 ,,! ,,obs]vatory2 #e4 ,,! ,,photographic ,,laboratory2 #f4 ,,! ,,photographic ,,enl>g]4 #a4 ,,gr9d+ ,,& ,,poli%+ ,,! ,,mirrors4 7#a47 ,,exp]im5ts ,,on ,a ,,metal ,,speculum4 ,my fir/ #ae in* speculum 0 an alloy ( copp] & t91 9 ! proportions giv5 by ,"l ,rosse4 ,8 g5]al directions 7 closely foll[$1 & ! ca/+ 0 v f9e1 free f pores1 & ( silv]y :it5ess4 ,x 0 #b in*es ?ick1 weigh$ #aaj p\nds1 & 0 int5d$ to be ( #ab feet focal l5g?4 ,! gr9d+ & poli%+ 7 conduct$ ) ! ,rosse ma*9e4 ,al?\gh a great am\nt ( "t 0 sp5t 9 v>i\s trials1 ext5d+ ov] m ?an a ye>1 a f9e figure 0 nev] obta9$--! pr9cipal ob/acle to success be+ a t5d5cy to poli% 9 r+s ( diff]5t focal l5g?4 ,x mu/1 h[ev]1 be borne 9 m9d t ,"l ,rosse _h s ?or\ghly ma/]$ ! peculi>ities ( 8 ma*9e z to produce ) x ! l>ge/ specula ev] made & ( v f9e figure4 ,dur+ ^! exp]im5ts !re 0 occasion to gr9d out "s imp]fections1 #h_/ajj ( an in* deep1 f ! face ( ! metal4 ,?is op]ation 0 greatly assi/$ by /opp+ up ! defects ) a ?ick alcoholic solution ( ,canada balsam1 & hav+ made a rim ( wax ar\nd ! edge ( ! mirror1 p\r+ on nitro-hydro*loric acid1 :i* quickly corrod$ away ! uncov]$ spaces4 ,subsequ5tly an increase 9 focal l5g? ( #ae in*es 0 accompli%$1 by attack+ ! edge zones ( ! surface ) ! acid 9 graduat$ dep?s4 ,an attempt also 0 made to assi/ ! t$i\s gr9d+ op]ation by includ+ ! gr9d] & mirror 9 a ,voltaic circuit1 mak+ ! speculum ! positive pole4 ,by decompos+ acidulat$ wat] betwe5 x & ! gr9d]1 & !reby oxidiz+ ! t9 & copp] ( ! speculum1 ! op]ation 0 mu* facilitat$1 b ! batt]y surface requir$ 0 too great = common use4 ,if a suffici5t int5sity 0 giv5 to ! curr5t1 speculum metal 0 transf]r$ )\t oxidation to ! gr9d]1 & deposit$ 9 ?9 lay]s ^u x4 ,x 0 propos$ at "o "t to make use ( ?is fact1 & coat a mirror ( brass ) a lay] ( speculum metal by electrotyp+4 ,! ga9 9 lightness w\ld be consid]able4 ,dur+ ! w9t] ( #ahfj ! speculum 0 split into two pieces1 by ! expansion 9 freez+ ( a few drops ( wat] t _h f\nd _! way into ! support+ case4 7#b47 ,silv]+ ,glass4 ,at ,sir ,john ,h]s*el's sugge/ion 7giv5 on ! occasion ( a visit t my fa!r paid him 9 #ahfj71 exp]im5ts 7 next comm5c$ ) silv]$ glass specula4 ,^! 7 describ$ z possess+ great capabilities = a/ronomical purposes4 ,!y reflect m ?an #ij p] c5t4 ( ! light t fulls ^u !m1 & only weigh "o-eigh? z mu* z specula ( metal ( equal ap]ture4 ,z no details ( ,/e9heil's or ,f\cault's processes = silv]+ 9 ! cold way 7 accessible at ! "t1 trials ext5d+ at int]vals ov] f\r mon?s 7 made4 ,a v>iety ( r$uc+ ag5ts 7 us$1 & ev5tually good results obta9$ ) milk sug>4 ,soon aft] a description ( ! process resort$ to by ,m4 ,f\cault 9 8 excell5t exp]im5ts 0 procur$4 ,x consi/s 9 decompos+ an alcoholic solution ( ammonia & nitrate ( silv] by oil ( cloves4 ,! prep>ation ( ! solutions & putt+ !m 9 a prop] /ate ( in/ability are v difficult1 & ! results by no means c]ta94 ,! silv] is apt to be s(t & easily rubb$ (f1 or ( a lead5 appe>ance4 ,x is liable to become spott$ f adh]5t p>ticles ( ! solutions us$ 9 its prep>ation1 & (t5 :5 dissolv$ (f a piece ( glass ) nitric acid leaves a r$di% p[d]4 ,occasionally1 h[ev]1 ! process gives excell5t results4 ,9 ! w9t] ( #ahfa1 ,m4 ,cimeg publi%$ 8 me?od ( silv]+ look+-glasses by t>trate ( pota% & soda 7,ro*elle salt74 ,s9ce ,i h made modifications 9 x fitt+ ! silv] = be+ poli%$ on ! rev]se side1 ,i h nev] on any occasion fail$ to secure bright1 h>d1 & 9 e respect1 p]fect films4 ,! op]ation1 :i* 9 _m details resembles t ( ,m4 ,f\cault1 is divid$ into3 #a/1 clean+ ! glass2 #b;d1 prep>+ ! solutions2 #c;d1 w>m+ ! glass2 #d?1 imm]sion 9 ! silv] solution & /ay !re2 #e?1 poli%+4 ,x %\ld be c>ri$ on 9 a room w>m$ to #gj ,f4 at lea/4 ,! description is = a #ae-a_/b in* mirror4 #a/4 ,clean ! glass l a plate = collodion photography4 ,rub x ?or\ghly ) nitric acid1 & !n wa% x well 9 pl5ty ( wat]1 & set x on edge on filt]+ pap] to dry4 ,!n cov] x ) a mixture ( alcohol & prep>$ *alk1 & all[ evaporation to take place4 ,rub x 9 succession ) _m pieces ( cotton flannel4 ,?is leaves ! surface almo/ *emically clean4 ,lately1 in/ead ( *alk ,i h us$ pla9 uniodiz$ collodion1 & poli%$ ) a fre%ly-wa%$ piece ( cotton flannel1 z soon z ! film _h become semi-solid4 #b;d4 ,dissolve #efj gra9s ( ,ro*elle salt 9 two or ?ree ounces ( wat] & filt]4 ,dissolve #hjj gra9s ( nitrate ( silv] 9 f\r ounces ( wat]4 ,take an ounce ( /rong ammonia ( comm]ce1 & add nitrate solution to x until a br[n precipitate rema9s undissolv$4 ,!n add m ammonia & aga9 nitrate ( silv] solution4 ,?is alt]nate addition is to be c>efully cont9u$ until ! silv] solution is exhau/$1 :5 "s ( ! br[n precipitate %\ld rema9 9 susp5sion4 ,! mixture !n conta9s an undissolv$ excess ( oxide ( silv]4 ,filt]4 ,j be=e us+1 mix ) ! ,ro*elle salt solution1 & add wat] en\gh to make #bb ounces4 ,illu/ration3 ,fig4 #a4 ,! ,silv]+ ,vessel4 ,! vessel 9 :i* ! silv]+ is to be p]=m$ may be a circul> di% 7,fig4 #a7 ( ord9>y t9plate1 #af-a_/b in*es 9 diamet]1 ) a flat bottom & p]p5dicul> sides "o in* high1 & coat$ inside ) a mixture ( beeswax & ros9 7equal p>ts71 ,at opposite ends ( "o diamet] two n>r[ pieces ( wood1 a a1 #a_/h ( an in* ?ick1 are cem5t$4 ,!y are to keep ! face ( ! mirror f ! bottom ( ! vessel1 & p]mit ( a rock+ motion be+ giv5 to ! glass4 ,be=e us+ su* a vessel1 x is necess>y to t\* any cracks t may h =m$ 9 ! wax ) a hot pok]4 ,a _s lamp causes bubbles & holes ?r\gh to ! t94 ,! vessel too mu/ always1 especially if p>tly silv]$1 be clean$ ) nitric acid & wat]1 & left fill$ ) cold wat] till ne$$4 ,in/ead ( ! above1 ,india-rubb] ba?s h be5 occasionally us$4 #c;d4 ,9 ord] to secure f9e & h>d deposits 9 ! %orte/ "t & ) weak solutions1 x is desirable1 ?\gh n necess>y1 to w>m ! glass slightly4 ,?is is be/ done by putt+ x 9 a tub or o!r suitably siz$ vessel1 & p\r+ 9 wat] en\gh to cov] ! glass4 ,!n hot wat] is gradually /irr$ 91 till ! mixture rea*es #ajj ,f4 ,x is also advantage\s to place ! vessels conta9+ ! +r$i5ts = ! silv]+ solution 9 ! same ba? = a %ort "t4 #d?4 ,on tak+ ! glass out ( ! w>m wat]1 c>ry x to ! silv]+ vessel--into :i* an assi/ant has j previ\sly p\r$ ! mix$ silv]+ solution--& imm$iately imm]se x face d[nw>ds1 dipp+ 9 fir/ "o edge & !n quickly lett+ d[n ! o!r till ! face is horizontal4 ,! back ( c\rse is n cov]$ ) ! fluid4 ,! same precautions are necess>y to avoid /reaks 9 silv]+ z 9 ! case ( putt+ a collodion plate 9 ! ba?4 ,place ! :ole app>atus be=e a w9d[4 ,keep up a sl[ rock+ motion ( ! glass1 & wat* = ! appe>ance ( ! bright silv] film4 ,! solution quickly turns br[n1 & ! silv] soon aft] appe>s1 usually 9 f ?ree to five m9utes4 ,leave ! mirror 9 ! liquid ab\t six times z long4 ,at ! expiration ( ! tw5ty m9utes or half h\r lift x out1 & look ?r\gh x at "s v bright object4 ,if ! object is sc>cely visible1 ! silv] surface mu/ !n be wa%$ ) pl5ty ( wat]1 & set on edge on bibul\s pap] to dry4 ,if1 on ! contr>y1 x is too ?91 put x quickly back1 & leave x until ?ick en\gh4 ,:5 poli%$ ! silv] ought1 if held betwe5 ! eye & ! sun1 to %[ 8 disk ( a light blue t9t4 ,on com+ out ( ! ba? ! metallic surface %\ld h a rosy gold5 color by reflect$ light4 #e?4 ,:5 ! mirror is ?or\ghly dry1 & no drops ( wat] rema9 ab\t ! edges1 lay x ^u its back on a ?or\ghly du/$ table4 ,take a piece ( ! s(te/ ?9 bucksk91 & /uff x loosely ) cotton to make a rubb]4 ,avoid us+ ! edge pieces ( a sk91 z !y are always h>d & conta9 nodules ( lime4 ,g g5tly ov] ! :ole silv] surface ) ?is rubb] 9 circul> /rokes1 9 ord] to comm5ce ! removal ( ! rosy gold5 film1 & to cond5se ! silv]4 ,!n hav+ put "s v f9e r\ge on a piece ( bucksk9 laid flat on ! table1 impregnate ! rubb] ) x4 ,! be/ /roke = poli%+ is a motion 9 small circles1 at times go+ gradually r\nd on ! mirror1 at times across on ! v>i\s *ords 7,fig4 #b74 ,at ! end ( an h\r ( cont9u\s g5tle rubb+1 ) occasional t\*es on ! flat r\g$ sk91 ! surface w be poli%$ s z to be p]fectly black 9 oblique positions1 &1 ) ev5 mod]ate c>e1 scrat*less4 ,! process is l a burni%+4 ,put ! rubb] c>efully away = ano!r occasion4 ,illu/ration3 ,fig4 #b4 ,poli%+ ,/rokes4 ,! ?ickness ( ! silv] ?us deposit$ is ab\t #a_/bjj1jjj ( an in*4 ,gold leaf1 :5 equally transp>5t1 is e/imat$ at ! same fraction4 ,! actual value ( ! am\nt on a #ae-a_/b in* mirror is n q a c5t--! weight be+ less ?an #d gra9s 7#bci milligrammes on "o occasion :5 ! silv] 0 unusually ?ick71 if ! directions above giv5 are foll[$4 ,v>iations 9 ?ickness ( ?is film ( silv] on v>i\s p>ts ( ! face ( ! mirror are consequ5tly only small fractions ( #a_/bjj1jjj ( an in*1 & are !re=e ( no optical mom5t :atev]4 ,if a glass has be5 prop]ly silv]$1 & %[s ! sun ( ! same color & int5sity ?r\gh all p>ts ( its surface1 ! mo/ delicate optical te/s w c]ta9ly fail to indicate any diff]5ce 9 figure betwe5 ! silv] & ! glass und]nea?4 ,! fa9te/ peculi>ities ( local surface se5 on ! glass by ! me?od ( ,m4 ,f\cault1 w be reproduc$ on ! silv]4 ,! durability ( ^! silv] films v>ies1 dep5d+ on ! circum/ances "u :i* !y are plac$1 & ! me?od ( prep>ation4 ,sulphurett$ hydrog5 t>ni%es !m quickly4 ,drops ( wat] may split ! silv] (f4 ,"u c]ta9 circum/ances1 too1 m9ute fissures w spread all ov] ! surface ( ! silv]1 & x w app>5tly lose its adhesion to ! glass4 ,?is ph5om5on seems to be connect$ ) a cont9u$ exposure to dampness1 & is avoid$ by gr9d+ ! edge ( ! concave mirror flat1 & keep+ x cov]$ :5 n 9 use ) a %eet ( flat plate glass4 ,heat seems to h no prejudicial effect1 ?\gh x might h be5 suppos$ t ! diff]5ce 9 expansibility w\ld h ov]come ! mutual adhesion4 ,g5]ally silv]$ mirrors are v endur+1 & w be> poli%+ repeat$ly1 if previ\sly dri$ by heat4 ,i h "s :i* h be5 us$ z diagonal reflectors 9 ! ,newtonian1 & h be5 expos$ dur+ a l>ge "p ( ! day to ! heat ( ! sun conc5trat$ by ! #ae-a_/b in* mirror4 ,^! small mirrors are nev] cov]$1 & yet ! "o n[ 9 ! telescope has be5 !re a ye>1 & has _h ! du/y film--l t :i* accumulates on glass--poli%$ (f x a doz5 times4 ,9 ord] to gu>d aga9/ t>ni%+1 exp]im5ts 7 at fir/ made 9 gild+ silv] films1 b 7 ab&on$ :5 f\nd to be unnecess>y4 ,a p>tial conv]sion ( ! silv] film into a gold5 "o1 :5 x w resi/ sulphurett$ hydrog51 c be accompli%$ z foll[s3 ,take ?ree gra9s ( hyposulphite ( soda1 & dissolve x 9 an ounce ( wat]4 ,add to x sl[ly a solution 9 wat] ( "o gra9 ( *loride ( gold4 ,a lemon yell[ liquid results1 :i* ev5tually becomes cle>4 ,imm]se ! silv]$ glass 9 x = tw5ty-f\r h\rs4 ,an ex*ange w take place1 & ! film become yell[i%4 ,i h a piece ( glass prep>$ 9 ?is way :i* rema9s unhurt 9 a box1 :]e o!r pieces ( pla9 silv]$ glass h *ang$ "s to yell[1 "s to blue1 f exposure to coal gas4 ,i h also us$ silv]$ glass plates = dagu]reotyp+4 ,!y iodize beautifully if fre%ly poli%$1 & ow+ probably to ! abs5ce ( ! usual copp] alloy ( silv] plat+1 take impressions ) v %ort exposures4 ,! result+ picture has a rosy w>m?1 r>ely se5 9 ord9>y dagu]reotypes4 ,! only precaution necess>y is 9 fix+ to use an alcoholic solution ( cyanide ( potassium1 in/ead ( hyposulphite ( soda dissolv$ 9 wat]4 ,! latt] has a t5d5cy to split up ! silv]4 ,! subsequ5t wa%+ mu/ be ) dilut$ common alcohol4 ,pictures obta9$ by ?is me?od w be> high magnify+ p[]s )\t %[+ granulation4 ,un=tunately ! exposure requir$ = !m 9 ! telescope is six times z great z = a s5sitive wet collodion1 ?\gh ! iodiz+ be c>ri$ to a lemon yell[1 ! bromiz+ to a rose r$1 & ! plate be return$ to ! iod9e4 7#c47 ,,gr9d+ ,,& ,,poli%+ ,,glass4 ,"s ( ! facts /at$ 9 ! foll[+ p>agraphs1 ! result ( num]\s exp]im5ts1 may n be new to practical opticians4 ,i h _h1 h[ev]1 to poli% ) my own h&s m ?an a hundr$ mirrors ( v>i\s sizes1 f #ai in*es to #a_/d ( an in* 9 diamet]1 & to exp]i5ce v frequ5t failures = ?ree ye>s1 be=e succe$+ 9 produc+ l>ge surfaces ) c]ta9ty & quickly4 ,x is well nigh impossible to obta9 f opticians ! practical m9uti :i* are ess5tial1 & :i* !y conceal ev5 f ea* o!r4 ,! long cont9u$ rese>*es ( ,"l ,rosse1 ,mr4 ,lassell1 & ,m4 ,f\cault are full ( ! mo/ valuable facts1 & h be5 ( cont9ual use4 ,! subject is divid$ into3 a4 ,! ,peculi>ities ( ,glass2 b4 ,em]y & ,r\ge2 c4 ,tools ( ,iron1 ,lead & ,pit*2 d4 ,me?ods ( ,exam9+ ,surfaces2 e4 ,ma*9es4 a4 ,peculi>ities ( ,glass4 ,effects ( ,pressure4--,x is g5]ally suppos$ t glass is possess$ ( ! p[] ( resi/ance to compression & rigidity 9 a v m>k$ mann]4 ,9 ! c\rse ( ^! exp]im5ts x has appe>$ t a %eet ( x1 ev5 :5 v ?ick1 c ) difficulty be set on edge )\t b5d+ s mu* z to be optically wor?less4 ,=tunately 9 e disk ( glass t ,i h tri$1 !re is "o diamet] on ei!r end ( :i* x may /& )\t h>m4 ,9 exam9+ lately v>i\s works on a/ronomy & optics1 x appe>s t ! same difficulty has be5 f\nd n only 9 glass b also 9 speculum metal4 ,%ort us$ always to m>k on ! edge ( ! l>ge mirrors ( 8 ,gregorian telescopes ! po9t :i* %\ld be plac$ upp]mo/1 9 case !y 7 remov$ f _! cells4 ,9 a*romatics ! image is v s5sibly *ang$ 9 %>pness if ! fl9t & cr[n are n 9 ! be/ positions2 & ,mr4 ,airy1 9 m\nt+ ! ,nor?umb]l& telescope1 _h to arrange ! means = turn+ ! l5ses on _! common axis1 until ! f9e/ image 0 atta9$4 ,9 no acc\nt1 h[ev]1 h ,i f\nd a critical /atem5t ( ! exact nature ( ! de=mation1 ! obs]v]s m]ely rem>k+ t 9 "s positions ( ! object glass !re 0 a %>p] image ?an 9 o!rs4 ,be=e ,i appreciat$ ! facts n[ to be m5tion$1 _m f9e mirrors 7 condemn$ to be re-poli%$1 :i*1 _h !y be5 prop]ly set 9 _! m\nt+s1 w\ld h op]at$ excell5tly4 ,9 attempt+ to asc]ta9 ! nature ( de=mations by pressure1 _m *anges 7 made 9 ! position ( ! disk ( glass1 & 9 ! k9d ( support4 ,"s squ>e mirrors1 too1 7 gr\nd & poli%$4 ,z an example ( ! f9al results1 ! foll[+ case is pres5t$3 ,a #ae-a_/b in* unsilv]$ mirror #a-a_/d in* ?ick 0 set ) its be/ diamet] p]p5dicul>1 ! axis ( ! mirror be+ horizontal 7,fig4 #h74 ,! image ( a p9-hole illum9at$ by a lamp 0 !n obs]v$ to be s+le1 %>ply def9$1 & ) int]f]5ce r+s surr\nd+ x z at a1 ,fig4 #c4 ,on turn+ ! glass #ij degrees1 t is "o qu>t] way r\nd1 its axis /ill po9t+ 9 ! same direction1 x c\ld h>dly be realiz$ t ! same concave surface 0 conv]g+ ! rays4 ,! image 0 sep>at$ into two ( ab\t equal int5sity1 z at b1 ) a w+ ( light go+ out above & bel[ f ! junction4 ,inside & outside ( ! focal plane ! cone ( rays _h an elliptical section1 ! major axis be+ horizontal inside1 & p]p5dicul> outside4 ,turn+ ! mirror /ill m r\nd ! image gradually improv$1 until ! orig9al diamet] 0 p]p5dicul> aga9--! end t _h be5 ! upp]mo/ n[ be+ ! l[e/4 ,a simil> s]ies ( *anges occurr$ 9 support+ ! glass on v>i\s p>ts ( ! o!r semicircle4 ,x might be suppos$ t irregul>ities on ! edge ( ! glass disk1 or 9 ! support+ arc w\ld acc\nt = ! ph5om5a4 ,b two facts dispose ( ! =m] ( ^! hypo!ses3 9 ! fir/ place if ! glass be turn$ exactly half way r\nd1 ! "* ( ! image is un*ang$1 & x is n to be believ$ t 9 _m diff]5t mirrors ?is c\ld occur by *ance co9cid5ce4 ,9 ! second place1 "o ( ^! mirrors has be5 c>efully exam9$ aft] be+ gr\nd & poli%$ ?ree times 9 succession1 & on ea* occasion requir$ ! same diamet] to be p]p5dicul>4 ,z to ! second hypo!sis no mat]ial diff]5ce is obs]v$ :e!r ! support+ arc bel[ be l>ge or small1 nor :5 x is replac$ by a ?9 semicircle ( t9plate l9$ ) cotton wool4 ,illu/ration3 ,fig4 #c4 ,effect ( ,pressure on a ,reflect+ ,surface4 ,i am l$ to believe t ?is peculi>ity results f ! /ructural arrangem5t ( ! glass4 ,! specim5s t h s]v$ = ^! exp]im5ts h probably be5 subject$ to a roll+ op]ation :5 9 a pla/ic /ate1 9 ord] to be r$uc$ to a uni=m ?ickness4 ,optical glass1 :i* may be made by s(t5+ d[n irregul> fragm5ts into m\lds at a temp]ature bel[ t ( fusion1 may h ! same difficulty1 b :e!r x has a diamet] ( m9imum compression c only be det]m9$ by exp]im5t4 ,:y speculum metal %\ld h ! same prop]ty might be asc]ta9$ by a critical exam9ation ( ! process ( ca/+1 & ! effect ( ! position ( ! op5+s 9 ! m\ld = ! entrance ( ! molt5 metal4 ,effects ( ,heat4--,! prec$+ *anges 9 glass :5 isolat$ appe> v simple1 & _! rem$y1 to keep ! prop] diamet] p]p5dicul>1 is s obvi\s t x may seem surpris+ t !y %\ld h giv5 orig9 to any emb>rassm5t4 ,9 fact x is n[ desirable to h a disk 9 :i* !y are well m>k$4 ,b 9 practice !y are complicat$ 9 ! mo/ try+ mann] ) v>iations produc$ by heat p]vad+ ! v>i\s p>ts ( ! glass unequally4 ,! foll[+ case illu/rates ! effects ( heat3-- ,illu/ration3 ,fig4 #d4 ,effects ( ,heat on a ,reflect+ ,surface4 ,a #ae-a_/b in* mirror1 :i* 0 giv+ at its c5tre ( curvature a v f9e image 7a1 ,fig4 #d7 ( an illum9at$ p9-hole1 0 heat$ at ! edge by plac+ ! "r h& on ! back ( ! mirror1 at "o end ( ! horizontal diamet]4 ,9 a few seconds an arc ( light came out f ! image z at b1 & on putt+ ! left h& on ! o!r extremity ( ! same diamet] ! appe>ance c 0 t ( two arcs ( light cross+ ea* o!r1 & hav+ an image at ea* int]section4 ,! mirror did n recov] its orig9al condition 9 t5 m9utes4 ,ano!r p]son on a subsequ5t occasion t\*+ ! ends ( ! p]p5dicul> diamet] at ! same "t t ! horizontal 7 w>m$1 caus$ ! image d to become some:at l two ( c1 put at "r angles to ea* o!r4 ,a little di/ance outside ! focus ! complem5t>y appe>ances1 b1 c1 d1 7 f\nd4 ,by unsymmetrical w>m+ /ill m rem>kable =ms em]g$ 9 succession1 "s ( :i* 7 m l c]ta9 nebul ) _! milky light1 ?an any regul> geometrical figure4 ,if ! glass _h1 aft] "o ( ^! exp]im5ts1 be5 imm$iately put on ! poli%+ ma*9e & re-poli%$1 ! *anges 9 surface w\ld to a c]ta9 ext5t h become p]man5t1 z 9 ,*9ese specula1 & ! mirror w\ld h requir$ ei!r re-gr9d+ or prolong$ poli%+ to get rid ( !m4 ,?is occurr$ un=tunately v frequ5tly 9 ! e>li] /ages ( ?is s]ies ( exp]im5ts1 & gave orig9 on "o occasion to a surface :i* c\ld only %[ ! image ( a p9-hole z a loz5ge 7b1 ,fig4 #e71 ) an image at ea* angle inside ! focus1 & z an image a ) f\r w+s outside4 ,illu/ration3 ,fig4 #e4 ,effects ( ,heat r5d]$ p]man5t4 ,b x mu/ n be suppos$ t su* app>5t causes z ^! are requir$ to di/urb a surface injuri\sly4 ,frequ5tly mirrors 9 ! process = correction ( sph]ical ab]ration w *ange ! quality ( _! images )\t any p]ceptible reason = ! alt]ation4 ,a curr5t ( cold or w>m air1 a gleam ( sunlight1 ! close approa* ( "s p]son1 an ungu>d$ t\*1 ! application ( cold wat] injudici\sly w ru9 ! labor ( days4 ,! avoidance ( ^! & simil> causes requires p]sonal exp]i5ce1 & ! amateur c only be advis$ to use too mu* caution r ?an too little4 ,su* accid5ts1 too1 tea* a useful lesson 9 ! managem5t ( a l>ge telescope1 nev]1 = in/ance1 to leave "o-half ! mirror or l5s expos$ to radiate into cold space1 :ile ! o!r half is cov]$ by a comp>atively w>m dome4 ,"u ! head ( ! ,sun-,cam]a1 "s fur!r facts ( ?is k9d may be f\nd4 ,oblique ,mirrors4--,/ill ano!r prop5sity ( glass & speculum metal mu/ be not$4 ,a truly sph]ical concave c only give an image free f di/ortion :5 x is s set t its optical axis po9ts to ! object & returns ! image directly back t[>ds x4 ,b ,i h poli%$ a l>ge numb] ( mirrors 9 :i* an image free f di/ortion 0 produc$ only :5 oblique p5cils fell on ! mirror1 & ! image 0 return$ along a l9e =m+ an angle ( f #b to #c degrees ) ! direction ( ! object4 ,su* mirrors1 ?\gh exactly suit$ = ! ,h]s*elian con/ruction1 w n (ficiate 9 a ,newtonian unless ! diagonal mirror be put en\gh out ( c5tre 9 ! tube1 to comp5sate = ! figure ( ! mirror4 ,"s ( ! be/ photographs ( ! moon t h be5 produc$ 9 ! obs]vatory1 7 made :5 ! diagonal mirror 0 #f in*es out ( c5tre 9 ! #af in* tube4 ,( c\rse ! l>ge mirror bel[ 0 n p]p5dicul> to ! axis ( ! tube1 b 0 incl9$ #b #cb4 ,! figure ( su* a concave might be expla9$ by ! supposition t x 0 z if cut out ( a p>abolic surface ( twice ! diamet]1 s t ! v]tex %\ld be on ! edge4 ,b if ! mirror 0 turn$ #ahj x app>5tly did j z well z 9 ! fir/ position1 ! image ( a r\nd object be+ nei!r oval nor elliptical1 & )\t w+s4 ,! image1 h[ev]1 is nev] q z f9e z 9 ! usual k9d ( mirrors4 ,! true explanation seems r to be t ! radius ( curvature is great] along "o ( ! diamet]s ?an along t at "r angles4 ,h[ x is possible = su* a figure to arise dur+ gr9d+ & poli%+ is n easy to und]/&1 unless x be grant$ t glass yields m to heat & compression 9 "o direction ?an ano!r4 ,aft] ^! facts _h be5 labori\sly asc]ta9$1 & ! me?od ( us+ su* o!rwise valueless mirrors put 9 practice z above /at$1 *ance br\ght a lett] ( ,maskelyne to my notice4 ,he says1 8,i hit ^u an extraord9>y exp]im5t :i* greatly improv$ ! p]=mance ( ! six-feet reflector04444 ,x 0 "o made by ,%ort4 8,z a l managem5t may improve _m o!r telescopes1 ,i %all "h relate x3 ,i remov$ ! great speculum f ! position x ought to hold p]p5dicul> to ! axis ( ! tube :5 ! telescope is said to be rightly adju/$1 to "o a little incl9$ to ! same & f\nd a c]ta9 incl9ation ( ab\t #b-a_/b 7z ,i f\nd by ! alt]ation ( objects 9 ! f9] "o ( ,dollond's be/ night glasses ) a field ( #f71 :i* caus$ ! telescope to %[ ! object 7a pr9t$ pap]7 incomp>ably bett] ?an be=e2 insomu* t ,i c\ld read _m ( ! words :i* be=e ,i c\ld make no?+ at all (4 ,x is pla91 !re=e1 t ?is telescope %[s be/ ) a c]ta9 oblique p5cil ( rays4 ,probably x w be f\nd t ?is circum/ance is by no means peculi> to ?is telescope40 ,?is v valuable obs]vation has la9 buri$ = eighty-two ye>s1 & ignorance ( x has l$ to ! de/ruction ( _m a valuable surface4 ,z reg>ds ! me?od ( combat+ ?is t5d5cy1 x is z a g5]al rule be/ to re-gr9d or r re-f9e ! surface1 = ?\gh pit* poli%+ has occasionally correct$ x 9 a few m9utes1 x w n always d s4 ,i h poli%$ a surface = ?irte5 & a half h\rs1 exam9+ x frequ5tly1 )\t *ang+ ! obliquity 9 ! slighte/ degree4 ,glass1 !n1 is a sub/ance prone to *ange by heat & compression1 & requir+ to be h&l$ ) ! utmo/ caution4 b4 ,em]y & ,r\ge4 ,9 ord] to excavate ! concave depression 9 a piece ( glass1 em]y z co>se z ! head ( a p9 has be5 commonly us$4 ,?is cuts rapidly1 & is succe$$ by f9] gra9$ v>ieties1 till fl\r em]y is rea*$4 ,aft] t only wa%$ em]ies %\ld be p]mitt$4 ,!y are made by an elutriat+ process inv5t$ by ,dr4 ,gre54 ,five p\nds ( ! f9e/ sift$ fl\r em]y are mix$ ) an ounce ( pulv]iz$ gum arabic4 ,en\gh wat] to make ! mass l treacle is !n add$1 & ! +r$i5ts are ?or\ghly incorporat$ by ! h&4 ,!y are put into a deep j> conta9+ a gallon ( wat]4 ,aft] be+ /irr$ ! fluid is all[$ to come to re/1 & ! surface be skimm$4 ,at ! end ( an h\r ! liquid conta9+ extremely f9e em]y 9 susp5sion is decant$ or drawn (f ) a siphon1 ne>ly d[n to ! level ( ! precipitat$ em]y at ! bottom1 & set aside to subside 9 a tall vessel4 ,:5 ?is has occurr$1 :i* w be 9 ! lapse ( a few h\rs1 ! fluid is to be c>efully p\r$ back into ! fir/ vessel1 & ! f9e deposit 9 ! second put into a /opp]$ bottle4 ,9 ! same way by /irr+ up ! precipitate aga91 em]y t has be5 susp5d$ #cj1 #aj1 #c1 #a m9utes1 & #bj1 #c1 seconds is to be secur$ & pres]v$ 9 wide-m\!d vessels4 ,! quantity ( ! f9] em]ies consum$ 9 smoo?+ a #ae-a_/b in* surface is v trifl+--a mass ( ea* z l>ge z two peas suffic+4 ,r\ge1 or p]oxide ( iron1 is bett] b\ght ?an prep>$ by ! amateur4 ,x is made by calc9+ sulphate ( iron & wa%+ ! product 9 wat]4 ,?ree k9ds are usually f\nd 9 comm]ce3 a v co>se v>iety conta9+ ! l>ge/ p]c5tage ( ! cutt+ black oxide ( iron1 :i* w scrat* glass l qu>tz2 a v f9e v>iety :i* c h>dly poli% glass1 b is suitable = silv] films2 & "o int]m$iate4 ,trial ( sev]al boxes is ! be/ me?od ( procur+ t :i* is desir$4 c4 ,tools ( ,iron1 ,lead1 & ,pit*4 ,9 mak+ a mirror1 "o ( ! fir/ /eps is to describe ^u two /\t %eets ( brass or iron1 arcs ( a circle ) a radius equal to twice ! desir$ focal l5g?1 & to secure1 by fil+ & gr9d+ !m toge!r1 a concave & convex gauge4 ,:5 ! radius b> is v long1 x may be hung aga9/ ! side ( a h\se4 ,by ! assi/ance ( ^! templets1 ! convex tools ( lead & iron & ! concave surface ( ! mirror are made p>ts ( a sph]e ( prop] diamet]4 ,! excavation ( a l>ge flat disc ( glass to a concave is be/ accompli%$ by means ( a ?ick plate ( lead1 ca/ consid]ably m convex ?an ! gauge4 ,! c5tral p>ts we> away v quickly1 & :5 !y become too flat mu/ be made convex aga9 by /rik+ ! lead on ! back ) a hamm]4 ,! glass is ?us caus$ gradually to approa* ! "r concavity4 ,t5 or twelve h\rs usually suffice to complete ?is /age4 ,! progress ( ! excavat+ is te/$ suffici5tly well by sett+ ! convex gauge on a diamet] ( ! mirror1 & obs]v+ h[ _m slips ( pap] ( a def9ite ?ickness w pass "u ! c5tre or edge1 z ! case may be4 ,?is avoids ! necessity ( a sph]omet]4 ,! ?ickness ( pap] is f\nd correctly en\gh by measur+ a half ream1 & divid+ by ! numb] ( %eets4 ,9 ?is mann] diff]5ces 9 ! v]s$ s9e ( a ?\s&? ( an in* may be appreciat$1 & a close en\gh approximation to ! desir$ focal l5g? rea*$--! precision requir$ 9 a*romatics n be+ ne$$4 ,! prep>ation ( ! iron tools on :i* ! gr9d+ is to be f9i%$ is v labori\s :]e p]sonal ex]tion is us$4 ,!y require to be ca/ ?9 9 ord] t !y may be easily h&l$1 & h5ce _c be turn$ ) v great exactness4 ,! pair = my l>ge mirrors are #ae-a_/b in*es 9 diamet]1 & 7 ca/ #c_/h ( an in* ?ick1 be+ /r5g!n$ h[ev] on ! back by eight ribs #c_/d ( an in* high1 radiat+ f a solid c5tre two in*es 9 diamet] 7a1 ,fig4 #f74 ,!y weigh$ #be p\nds apiece4 ,f\r e>s1 ) a tapp$ hole 9 ea*1 project at equal di/ances r\nd ! edge1 & s]ve ei!r z a means ( atta*m5t = a c\nt]poise lev]1 or z h&les4 ,illu/ration3 ,fig4 #f4 ,! ,iron ,gr9d]4 ,aft] ^! 7 turn$ & tak5 (f ! la! *uck1 !y 7 f\nd to be some:at sprung1 & _h to be scrap$ & gr\nd 9 ! ma*9e = a week be=e fitt+ prop]ly4 ,! sl[ness 9 gr9d+ results f ! em]y becom+ imb$d$ 9 ! iron1 & =m+ a surface z h>d z adamant4 ,once acquir$1 su* gr9d]s are v valuable1 z !y keep _! focal l5g? & figure app>5tly )\t *ange if c>efully us$1 & only work$ on glass ( ne>ly simil> curvature4 ,at fir/ no grooves 7 cut ^u ! face1 = 9 ! lead previ\sly employ$ = f9+ !y 7 f\nd to be a fruitful s\rce ( scrat*es1 on acc\nt ( gra9s ( em]y imb$d+ 9 !m1 & gradually break+ loose z ! lead wore away4 ,subsequ5tly x appe>$1 t unless !re 0 "s means ( spread+ wat] & ! gr9d+ p[d]s ev5ly1 r+s 7 likely to be produc$ on ! mirror1 & ! iron 0 consequ5tly treat$ z foll[s3-- ,a numb] ( pieces ( wax1 su* z is us$ 9 mak+ artificial fl[]s1 7 procur$4 ,! convex iron 0 laid out 9 squ>es ( #c_/d ( an in* on ! side1 & ea* alt]nate "o be+ t\*$ ) a ?ick alcoholic solution ( ,canada balsam1 a piece ( wax ( t size 0 put ov] x4 ,?is 0 f\nd aft] _m trials to be ! be/ me?od ( protect+ "s squ>es1 & yet leav+ o!rs 9 ! mo/ suitable condition to be attack$4 ,a rim ( wax1 melt$ ) ,canada balsam1 0 rais$ ar\nd ! edge ( ! iron1 & a p9t ( aqua regia p\r$ 94 ,9 a %ort "t ?is corrod$ out ! uncov]$ p>ts to a suffici5t dep?1 leav+ an appe>ance l a *ess-bo>d1 except t ! project+ squ>es did n t\* at ! adjo9+ angles 7b1 ,fig4 #f74 ,i %\ld h *ipp$ ! cavities out1 in/ead ( dissolv+ !m away1 b = fe> ( *ang+ ! radius ( curvature & break+ ! ?9 plate4 ,h[ev] z soon z ! iron 0 clean$1 x prov$ to h become flatt]1 ! radius ( curvature hav+ increas$ #g-c_/d in*es4 ,?is %[s :at a /ate ( t5sion & compression !re mu/ be 9 su* a mass1 :5 ! removal ( a film ( metal #a_/ej ( an in* ?ick1 "h & !re1 f "o surface1 causes s great a *ange4 ,:5 ! glass has be5 br\ght to ! f9e/ possible gra9 on su* a gr9d]1 a poli%+ tool has to be prep>$ by cov]+ ! convex iron ) ei!r pit* or ros94 ,^! sub/ances h v simil> prop]ties1 b ! ros9 by be+ cle> af=ds an opportunity ( see+ :e!r !re are impurities1 & !re=e has be5 frequ5tly us$1 /ra9+ be+ unnecess>y4 ,x is1 h[ev]1 too h>d z x occurs 9 comm]ce1 & requires to be s(t5$ ) turp5t9e4 ,a mass suffici5tly l>ge to cov] ! iron #a_/h ( an in* ?ick is melt$ 9 a porcela9 or metal capsule by a _s lamp4 ,:5 ?or\ghly liquid ! lamp is bl[n out1 & spirits ( turp5t9e add$1 a dra*m or two at a "t4 ,aft] ea* addition a *isel or "s simil> piece ( metal is dipp$ into ! fluid ros91 & !n imm]s$ 9 wat] at ! temp]ature ( ! room4 ,aft] a m9ute or two x is tak5 out1 & tri$ ) ! ?umb-nail4 ,:5 ! prop] degree ( s(tness is obta9$1 an ind5tation c be made by a mod]ate pressure4 ,! iron hav+ be5 heat$ 9 hot wat] is !n pa9t$ 9 /ripes #a_/h ( an in* deep ) ?is res9\s composition4 ,! glass concave to be poli%$ be+ sme>$ ) r\ge1 is press$ ^u x to secure a fit1 & ! iron is !n put 9 cold wat]4 ,) a n>r[ *isel /raight grooves are made1 divid+ ! surface into squ>es ( "o in*1 sep>at$ by int]vals ( "o-qu>t] ( an in* 7,fig4 #g74 ,"u c]ta9 circum/ances x is also desirable to take (f e o!r squ>e1 or p]haps r$uce ! poli%+ surface irregul>ly "h & !re1 to get an excess ( action on "s p>ticul> portion ( ! mirror4 ,illu/ration3 ,fig4 #g4 ,! ,poli%+ ,tool4 ,x is well1 on comm5c+ to poli% ) a tool made 9 ?is way1 to w>m ! glass z well z ! tool 9 wat] 7page #d7 be=e br++ ! two 9 contact4 ,if ?is is n done ! poli%+ w n g on k9dly1 a good adaptation n be+ secur$ = a l5g? ( "t1 & ! glass surface be+ injur$ at ! outset4 ,! ros9 on a poli%] put away = a day or two suff]s an int]nal *ange1 a species ( irregul> swell+1 & does n reta9 its orig9al =m4 ,heat+1 too1 has a good effect 9 prev5t+ di/urbance by local v>iations ( temp]ature 9 ! glass4 ,! description ( 8,local ,poli%]s0 w be giv5 "u ,ma*9es4 d4 ,me?ods ( ,exam9+ ,surfaces4 ,i h be5 9 ! habit ( te/+ mirrors exclusively at ! c5tre ( curvature1 n putt+ !m 9 ! telescope tube until ne>ly p>abolic or f9i%$4 ,! means ( trial are s excell5t1 ! indications obta9$ s precise1 & ! fre$om f atmosph]ic di/urbances s complete1 t ! greate/ facilities are (f]$ = asc]ta9+ ! nature ( a surface4 ,9 addition ! obs]v] is entirely indep5d5t ( day or night1 & ( ! wea!r4 ,i d n ?9k t any?+ m is le>n$ ( ! telescope1 ev5 "u favorable circum/ances1 ?an 9 ! work%op4 ,= ! improvem5t ( ^! me?ods ( obs]vation1 ,sci5ce is l>gely indebt$ to ,m4 ,f\cault1 ^: ?ird te/--! second 9 ! next p>agraph--is suffici5t to af=d by itself a l>ge "p ( ! in=mation requir$ 9 correct+ a concave surface4 ,!re are two di/9ct modes ( exam9ation3 #a/1 obs]v+ ) an eye-piece ! image ( an illum9at$ p9-hole at ! focus1 & ! cone ( rays inside & outside t plane2 #b;d1 receiv+ ! entire p5cil ( light com+ f ! mirror ?r\gh ! pupil on ! ret9a1 & notic+ ! di/ribution ( light & %ade1 & ! appe>ances 9 relief on ! face ( ! mirror4 ,illu/ration3 ,fig4 #h4 ,te/+ a ,concave at ! ,c5tre ( ,curvature4 ,! arrangem5ts = ^! te/s are z foll[s3 ,ar\nd ! flame ( a lamp 7a1 ,fig4 #h7 a %eet ( t9 is b5t s z to =m a cyl9drical scre54 ,?r\gh x at ! height ( ! brighte/ "p ( ! flame1 z at b1 two holes are bor$1 a qu>t] ( an in* ap>t1 "o #a_/cb ( an in* 9 diamet]1 ! o!r z small z ! po9t ( ! f9e/ ne$le w make--p]haps #a_/bjj ( an in*4 ,?is app>atus is to be set at ! c5tre ( curvature ( ! mirror c--! optical axis ( ! latt] be+ horizontal--& s adju/$ t ! light :i* div]ges f ! illum9at$ hole 9 use1 may1 aft] imp++ on ! concave surface ( ! glass1 return to =m an image close by ! side ( ! t9 scre54 ,9 ! case ( ! fir/ te/1 ! return+ rays are receiv$ into an eye-piece or microscope1 d1 magnify+ #bj times1 & mov+ ^u a divid$ scale to & f ! mirror4 ,9 ! second te/ ! eye-piece is remov$ away f be=e ! eye1 & a /raight-edg$ opaque scre51 e1 is put 9 its place4 ,! mirror is support$ 9 ^! trials by an arc ( wood f1 l9$ ) ?ick wooll5 /uff1 & above two wood5 lat*es1 g1 g1 prev5t x f fall+ =w>d1 b d n compress x4 ,x is1 ( c\rse1 unsilv]$4 ,9 ! figure ! table is repres5t$ v mu* clos] to ! mirror ?an x %\ld be4 ,9 trials on ! #ae-a_/b in* x has to be #be feet di/ant4 ,! appe>ance t a truly sph]ical concave surface pres5ts ) ! fir/ te/ is3 ! image ( ! hole is %>ply def9$ )\t any areola ( ab]ration ar\nd x1 & is surr\nd$ by int]f]5ce r+s4 ,inside & outside ! focus ! cone ( rays is exactly simil>1 & circul> 9 section4 ,x pres5ts no trace ( irregul> illum9ation1 nor any bright or d>k circles4 ,) ! second te/1 :5 ! eye is br\ght into su* a position t x receives ! :ole p5cil ( reflect$ rays1 & ! opaque scre5 is gradually drawn across 9 front ( ! pupil1 ! brightness ( ! surface sl[ly dim9i%es1 until j z ! scre5 is cutt+ (f ! la/ relic ( ! cone ( rays 7,fig4 #i71 ! mirror pres5ts an uni=m grayi% t9t1 foll[$ by total d>kness1 & gives to ! eye ! s5sation ( a plane4 ,illu/ration3 ,fig4 #i4 ,action ( ! ,opaque ,scre54 ,illu/ration3 ,fig4 #aj4 ,cau/ic ( ,oblate ,sph]oidal ,mirror4 ,if1 h[ev]1 ! mirror is n sph]ical1 b in/ead gradually decreases 9 focal l5g? t[>d ! edge1 ! foll[+ *anges result3 ,! image at ! be/ focus is surr\nd$ by a nebulosity1 /rong] z ! deviation f ! sph]e is great]1 & nei!r c a %>p focus be obta9$ nor int]f]5ce fr+es se54 ,9 ord] to include ?is nebulosity 9 ! image1 x w be necess>y to pu% ! eye-piece t[>d ! mirror4 ,be=e ! cone ( rays has complet$ its conv]g5ce1 ! mass ( light w be se5 to h accumulat$ at ! p]iph]y1 & aft] ! focus is pa/ & div]g5ce has comm5c$1 ! accumulation w be ar\nd ! axis4 ,t is1 a cau/ic 7,fig4 #aj7 is =m$ ) its summit f ! mirror4 ,by ! second te/1 9 gradually eclips+ ! light com+ f ! mirror1 j be=e all ! rays are ob/ruct$1 a "p ( ^? :i* h con/itut$ ! nebulosity w escape pa/ ! scre5 7,fig4 #aa7 into ! eye1 & cause !re an extremely exagg]at$ appe>ance 9 relief ( ! solid sup]pos$ ^u ! true surface b5ea?4 ,! glass w no long] seem to be a plane1 b to h a section z 9 ,fig4 #ab4 ,let u exam9e by ! aid ( ,m4 ,f\cault's diagrams :y x is t ! surface seems ?us curv$4 ,if ! dott$ l9e1 ,fig4 #ac1 repres5ts ! section ( ! mirror1 & ! solid l9e a section ( a sph]ical mirror ( ! same mean focal l5g?1 x w be se5 t ! curves t\* at two po9ts1 b are sep>at$ by an int]val else:]e4 ,if ?is int]val be project$ by means ( ! diff]5ces ( ! ord9ates1 ! result+ curve w be f\nd to be ! same z t :i* ! mirror app>5tly has4 ,illu/ration3 ,fig4 #ab4 ,app>5t ,section ( ,oblate ,sph]oidal ,mirror4 ,if ! opaque scre5 be drawn a %ort di/ance f ! mirror1 ! appe>ance ( ! section curve w seem to *ange1 ! bottom ( ! groove 7,fig4 #ab7 betwe5 ! c5tre & edge advanc+ inw>ds1 & ! m\nd 9 ! middle gr[+ small]4 ,if ! scre5 be pu%$ t[>d ! mirror ! rev]se takes place1 ! c5tral m\nd becom+ l>g]1 b ! edge decreas+4 ,! reason = ^! v>iations becomes app>5t by consid]+ ! ?ree diagrams1 ,fig4 #ad4 ,! dott$ curve 9 ea* in/ance repres5ts ! real curve ( ! mirror describ$ 9 ! la/ p>agraph1 :ile ! solid l9es are circles drawn ) radii progressionally %ort] 9 a1 b & c1 & repres5t sections ( ?ree sph]ical mirrors ^: focal l5g?s also progressively %ort54 ,illu/ration3 ,fig4 #aa4 ,action ( ! ,opaque ,scre54 ,illu/ration3 ,fig4 #ac4 ,section ( ,sph]ical & ,sph]oidal ,mirrors4 ,illu/ration3 ,fig4 #ad4 ,relation ( ,sph]es to ,oblate ,sph]oid4 ,:5 ! opaque scre5 is at a giv5 di/ance f ! mirror "u exam9ation1 ! only p>ts ( ! mirror :i* c (ficiate well are ^? :i* h a curvature correspond+ to a radius equal to ! same di/ance4 ,all ! o!r p>ts seem z if !y 7 cov]$ by project+ circul> masses4 ,9 look+ at ,fig4 #ad1 x is pla91 !n1 if ! opaque scre5 is at a maximum di/ance f ! mirror1 t ! c5tral p>ts alone w seem to op]ate1 because ! two curves 7a7 only t\* !re4 ,if ! scre5 is mov$ t[>d ! mirror ! curves 7b7 w co9cide at "s po9t betwe5 ! c5tre & edge1 :ile if c>ri$ /ill f>!r 9 only ! edges t\* & ! appe>ance w be z if a l>ge m\nd 7 fix$ ^u ! c5tre4 ,i h be5 c>eful 9 expla9+ h[ a surface may ?us seem to pres5t entirely diff]5t *>act]i/ics if exam9$ f po9ts ( view :i* v>y slightly 9 di/ance1 because a k ( ^! facts is ( ! utmo/ importance 9 correct+ su* an errone\s figure4 ,x is n[ obvi\s t ! correction w be equally effectual if ! mirror be poli%$ ) a small rubb] on ! edge1 or on ! c5tre1 or p>tly on ea*4 ,! only diff]5ce 9 ! result w be1 t ! mean focal l5g? w be increas$ 9 ! fir/ in/ance1 & decreas$ 9 ! second1 :ile x w rema9 un*ang$ 9 ! ?ird4 ,illu/ration3 ,fig4 #ae4 ,cau/ic ( ,hyp]bolic ,mirror4 ,illu/ration3 ,fig4 #af4 ,app>5t ,section ( ,hyp]bolic ,mirror4 ,if ! mirror1 in/ead ( hav+ a section l t ( an oblate sph]oid1 %\ld h ei!r an ellipse1 p>abola1 or hyp]bola1 z its section curve1 ! appe>ances se5 above are rev]s$4 ,:il/ by ! fir/ te/ !re is /ill an ab]ration r\nd ! image at ! be/ focus1 ! eye-piece mu/ n[ be drawn f ! mirror to include x4 ,! cone ( rays is mo/ d5se r\nd ! axis inside1 & at ! p]iph]y outside ! focus1 & ! summit ( ! cau/ic 7,fig4 #ae7 is turn$ t[>ds ! mirror4 ,! second te/ %[s a section z 9 ,fig4 #af1 a depression at ! c5tre1 & ! edges turn$ backw>ds4 ,! nature ( ! movem5t necess>y to r$uce ! surface to a sph]e is v pla9ly indicat$1 action on a zone a betwe5 ! c5tre & edge4 ,if1 h[ev]1 a p>abolic section is requir$1 ! zone a mu/ n be entirely remov$1 & ! surface r5d]$ app>5tly flat1 b z mu* ( x mu/ be left z exp]i5ce %[s to be desirable4 ,illu/ration3 ,fig4 #ag4 ,action ( ! ,opaque ,scre54 ,illu/ration3 ,fig4 #ah4 ,app>5t ,section ( ,mirror ) ,r+s4 ,if1 9 /ill a f\r? in/ance1 ! mirror is n =m$ by ! revolution ( any regul> curve ^u its axis1 b has ^u its surface zones ( long] & %ort] radius int]mix$ irregul>ly1 a v common case1 ! two te/s /ill indicate ) precision ! p>ts 9 fault1 & ! correction dem&$4 ,?us ! mirror se5 9 section 9 ,fig4 #ag1 :5 ! pr9cipal mass ( light 0 ob/ruct$ by ! opaque scre51 w\ld /ill p]mit t com+ f c]ta9 p>ts to f9d its way into ! eye4 ,figure #ah repres5ts an irregul> mirror1 t 0 produc$ 9 ! process ( correction ( a hyp]bolic surface1 :i* _h an app>5t section l ,fig4 #af previ\sly4 ,! zone a _h be5 act$ ^u ) a small local poli%]1 & ! mirror 0 f9i%$ by subsequ5tly s(t5+ d[n b & c ) a l>g] tool4 ,aft] hav+ ga9$ f ! prec$+ p>agraphs a g5]al idea ( ! value & nature ( ^! te/s at ! c5tre ( curvature1 a m p>ticul> description ( _! use is desirable4 ,m4 ,f\cault 9 8 me?ods fir/ br+s ! mirror to a sph]ical surface1 & !n by mov+ ! lum9\s p9-hole t[>d ! mirror1 & correspond+ly retract+ ! eye-piece or opaque scre51 c>ries x1 avoid+ ab]ration cont9ually by poli%+1 ?r\gh a s]ies ( ellipsoidal curvatures1 advanc+ /ep by /ep t[>d ! p>aboloid ( revolution4 ,! l5g? ( ! ap>tm5t1 h[ev]1 soon puts a t]m9ation to ?is gradual sy/em ( correction1 & he is =c$ to p]=m ! la/ /eps ( ! conv]sion by an empirical process1 & ev5tually to resort to trial 9 ! telescope4 ,) my mirrors ( #aej in*es focal l5g?1 dem&+ f ! outset a room m ?an #be feet long1 ?is successive sy/em _h to be ab&on$4 ,x 0 n f\nd feasible to place ! lamp 9 ! di/ant focus ( ! ellipse--! work%op be+ less ?an #cj feet long--& putt+ ! lum9\s s\rce on /&s outside1 introduc$ sev]al injuri\s complications1 n ! lea/ ( :i* 0 curr5ts 9 ! lay]s ( v>i\sly refract+ air 9 ! ap>tm5t4 ,9 a /ill room ! d5sity & hygrometric v>iations 9 its v>i\s p>ts only give rise to slight emb>rassm5t4 ,! mom5t1 h[ev]1 t curr5ts are produc$1 satisfactory exam9ation ( a mirror becomes difficult4 ,! air is se5 only too easily to move 9 great spiral convolutions betwe5 ! mirror & ! eye1 areol ( ab]ration appe> ar\nd a previ\sly excell5t image1 & 7 x n = ! second te/1 any det]m9ation ( surface w\ld be impossible4 ,by t te/ ! real deviations f tru? ( figure c be di/+ui%$ f ! atmosph]ic1 & to a practis$ eye suffici5t indications ( necess>y *anges giv54 ,su* a movem5t z t caus$ by plac+ ! h& 9 or "u ! l9e ( ! conv]g+ rays1 w completely de/roy ! beauty ( an image1 & by ! second te/ give orig9 9 ! fir/ case to ! appe>ance ,fig4 #ai4 ,9 ord] to be completely exempt at all times f arial difficulties1 x is desirable to h control ( a long und]gr\nd ap>tm5t1 ! op5+s ( :i* c be tightly clos$4 ,z no artificial w>m? is ne$$1 !re is ! m9imum ( movem5t 9 ! inclos$ air1 & conclusions respect+ a surface may be arriv$ at 9 a v %ort "t4 ,! mirror may also be support$ f ! gr\nd1 s t tremul\s vibrations :i* we>y ! eye1 & int]f]e ) ! accuracy ( criticism1 may be avoid$4 ,illu/ration3 ,fig4 #ai4 ,atmosph]ic ,motions4 ,driv5 !n f obs]v+ an image kept cont9ually free f ab]ration1 ?r\gh advanc+ ellipsoidal *anges1 x became necess>y to /udy ! gradual increase ( de=mation1 produc$ by ! great] & great] dep>tures f a sph]ical surface1 z ! p>abola 0 approa*$4 ,x 0 f\nd t a suffici5t guide is /ill provid$ 9 ^! te/s1 by modify+ !m prop]ly4 ,! longitud9al ab]ration ( a mirror ( small angul> op5+ is easily calculat$--be+ equal to ! squ>e ( half ! ap]ture1 divid$ by eight times ! pr9cipal focal l5g?4 ,t is1 if a #ae-a_/b in* mirror ( #aej in*es focal l5g? 7 sph]ical1 & 7 us$ to conv]ge p>allel rays1 ^? f its edge w\ld rea* a focus #e_/ajj ( an in* ne>] ! mirror ?an ^? f its c5tral p>ts4 ,if n[ ! conv]se exp]im5t be tri$1 & a mirror ( ! same size & focal l5g? :i* c conv]ge p>allel rays1 fall+ on all its p>ts1 to "o focus1 be exam9$ at ! c5tre ( curvature1 x gives !re an am\nt ( longitud9al ab]ration #aj_/ajj ( an in*1 equal to twice ! prec$+4 ,?is latt]1 !n1 is ! condition at ! c5tre ( curvature1 to :i* su* mirror mu/ be br\ght 9 ord] to conv]ge p>allel rays ) exactness4 ,9 addition1 /rict wat* mu/ be kept ^u ! zones int]m$iate betwe5 ! c5tre & edge1 bo? by measurem5t ) diaphragms ( _! ab]ration1 & bett] yet1 by obs]vation ( ! regul>ity ( ! curve ( t app>5t solid1 ,fig4 #af1 se5 by ! second te/4 ,?is modification ( ! fir/ te/ is lit]ally a me?od ( p>aboliz+ by measure1 & is capable ( great precision :5 ! eye le>ns to e/imate :]e ! exact focus ( a zone is4 ,! little irregul>ities f\nd r\nd ! edges ( ! holes ?r\gh ! t9 scre51 ,fig4 #h1 are 9 ?is respect ( mat]ial assi/ance4 ,!y %[1 too1 ! increas$ optical or p5etrat+ p[] t is ga9$ by increase ( ap]ture4 ,m9ute peculi>ities1 n visible "u v high p[]s ) a #aj in* diaphragm1 become imm$iately p]ceptible ev5 ) less magnify+ :5 ! :ole ap]ture is us$1 provid$ ! mirror is sph]ical4 ,illu/ration3 ,fig4 #bj4 ,adju/+ ! ,opaque ,scre54 ,9 ! use ( ! second te/ precautions h to be tak51 z may be inf]r$ f page #ae1 to set ! opaque scre5 exactly 9 ! prop] position4 ,! be/ me?od = asc]ta9+ its location is1 hav+ receiv$ ! image into ! eye1 plac$ purposely too ne> ! mirror1 to cause ! scre5 to move across ! cone ( rays f ! "r t[>ds ! left side4 ,a jet black %ad[ beg9s to advance at ! same "t1 & 9 ! same direction across ! mirror4 ,if ! eye is !n mov$ f ! mirror suffici5tly1 ?is black %ad[ c be made to orig9ate by ! same motion ( ! scre5 z be=e1 f ! left or opposite side ( ! mirror4 ,midway betwe5 ^! extremes !re is a po9t :]e ! advance is f nei!r side4 ,?is is ! true position = ! scre5 :5 x is desir$ to see ! imp]fections ( ! surface 9 highly exagg]at$ relief1 z 9 ,fig4 #bj1 :i* repres5ts ! appe>ance ( ,fig4 #ab4b #b ,9 ord] to exam9e ,fig4 #bj1 ! book %\ld be held ) ! left side ( ! page t[>d a w9d[ or lamp4 ,! eye %\ld also be at lea/ two feet di/ant4 ,! c5tre w !n be se5 to protrude1 & ! surface pres5t ! app>5t section engrav$ bel[ x4 ,! int]pretation ( ! lights & %ad[s ^u ! face ( a mirror 9 ?is te/ is always easy1 & ! obs]v] is n likely to mi/ake an elevation = a depression1 if he be>s 9 m9d ! fact t ! surface "u exam9ation mu/ always be reg>d$ z illum9at$ by an oblique light com+ f a s\rce on ! side opposite to t f :i* ! scre5 advances1 com+ = in/ance f ! left h& side1 9 ! above description4 ,9 practice1 ! diaphragms commonly us$ = a #ae-a_/b in* mirror h be5 z small z ! light f ! unsilv]$ surface w\ld all[4 ,a six in* ap]ture at ! c5tre1 a r+ an in* wide r\nd ! edge1 & a two in* zone midway betwe5 ! two4 e4 ,ma*9es4 ,9 ! beg9n+ ( ?is section ! difficulties into :i* ,i fell ) ,"l ,rosse's ma*9e 7 /at$4 ,^! caus$ x at ! "t to be ab&on$4 ,a ma*9e bas$ on ! same idea z ,mr4 ,lassell's beautiful app>atus 0 next con/ruct$4 ,x v>i$1 h[ev]1 9 ?is1 t ! hypocycloidal curve 0 describ$ p>tly by ! rotation ( ! mirror1 & p>tly by ! motions ( ! poli%]--! axes ( ! sp9dles c>ry+ ! two be+ capable ei!r ( co9cid5ce or lat]al sep>ation to a mod]ate ext5t4 ,a great deal ( "t & labor 0 exp5d$ 9 gr9d+ & poli%+ num]\s mirrors ) x1 b /ill ! difficulty t _h be5 s annoy+ 9 ! =m] ma*9e p]si/$4 ,frequ5tly1 9 fact g5]ally1 f six to eight zones ( unequal focal l5g? 7 visible1 al?\gh on "s occasions :5 ! mirror 0 hyp]bolic1 ! numb] 0 r$uc$ to two4 ,at fir/ x 0 suppos$ t ! fault lay ) ! poli%+1 ! pit* accumulat+ irregul>ly f be+ ( improp] s(tness1 = x 0 f\nd to be p>ticul>ly prone to heap up at ! c5tre4 ,b aft] ,i _h introduc$ a me?od ( f9e gr9d+ ) elutriat$ hone p[d]1 :i* enabl$ ! glass to reject light be=e ! pit* poli%+1 x became evid5t t ! zones 7 connect$ ) ! mode ( motion ( ! me*anism4 ,_m *anges 7 made 9 ! spe$ ( its v>i\s elem5ts1 & a contrivance to control ! irregul> motion ( ! poli%] introduc$1 b a really f9e & uni=m p>abolic surface 0 nev] obta9$1 ! v be/ %[+ :5 f9i%$ zones ( diff]5t focal l5g?s4 ,al?\gh x _c be said t ,i h tri$ ?is ma*9e ?or\ghly1 = ,mr4 ,lassell has produc$ specula ( exquisite def9+ p[] ) x1 & mu/ h avoid$ ^! imp]fections to a great ext5t1 yet ! evid5t necessity ( complicat+ ! movem5t#c consid]ably1 to avoid ! poli%+ 9 r+s1 l$ me to adopt an entirely diff]5t con/ruction1 :i* 0 us$ until q rec5tly4 ,al?\gh x has n[ be5 replac$ by ano!r ma*9e1 :i* is /ill bett] 9 pr9ciple1 & gives f9e results mu* m quickly1 yet z x produc$ "o p>abolic surface t bore a p[] ( m ?an #ajjj1 & z x s]ves to introduce ! process ( gr9d+1 x is wor?y ( description4 ,! action ( ma*9es = gr9d+ & poli%+ has be5 ?or\ghly exam9$ 9 my work%op1 no less ?an sev5 diff]5t ones hav+ be5 made at v>i\s times4 #c ,messrs4 ,de ,la ,rue & ,nasmy?1 :o us$ "o ( ,mr4 ,lassell's ma*9es1 z ,i h s9ce le>n$1 met ) ! same tr\ble1 & 7 l$ to make two additions to ! me*anism3 #a1 to control ! rotation ( ! poli%] rigor\sly2 & #b1 to give ! :ole speculum a lat]al motion1 by :i* ! int]sect+ po9ts ( ! curves describ$ by ! poli%] 7 regul>ly *ang$ 9 di/ance f ! c5tre ( ! mirror4 ,mr4 ,lassell _h previ\sly1 h[ev]1 introduc$ a contrivance = ?is latt] purpose himself4 ,! ma*9e1 :i* is a simplification ( ,"l ,rosse's1 0 int5d$ to give spiral /rokes4 ,x diff]$ f ! orig9al1 h[ev]1 9 dem&+ a *angeable /roke1 & 9 ! abs5ce ( ! lat]al motion4 ,9 ano!r mo/ ess5tial feature x v>i$ f bo? t & ,mr4 ,lassell's1 ! mirror 0 always upp]mo/ :ile poli%+1 & be+ unc\nt]pois$ escap$ to z great an ext5t z possible f ! effects ( irregul> pressure4 ,to any "o :o has /udi$ ! de=mations ( a reflect+ surface1 & kn[s h[ tr\blesome x is to support a mirror prop]ly1 ! advantage is app>5t4 ,illu/ration3 ,fig4 #ba4 ,poli%+ ,ma*9e4 ,illu/ration3 ,fig4 #bb4 ,! ,foot ,p[]4 ,! con/ruction is z foll[s3 ,a /\t v]tical %aft1 a1 ,fig4 #ba1 c>ries at its top a circul> table b1 ^u :i* ! poli%] c is screw$4 ,bel[ a b&-:eel d is fix$4 ,above ! table1 at a di/ance ( f\r in*es1 a horizontal b> e is arrang$1 s z to move back & =w>d 9 ! direction ( its l5g?1 & to c>ry ) x by means ( a screw l1 ! mirror m1 & its iron back or *uck n4 ,! b> is mov$ by a connect+ rod f1 atta*$ to x at "o end1 & at ! o!r to a p9 g mov+ a slot4 ,?is slot is 9 a crank h1 c>ri$ by a v]tical %aft i1 ne> ! =m] "o a4 ,! b&-:eel k is connect$ ) ! foot p[]1 ,fig4 #bb4 ,! ma*9e1 except ^? p>ts liable to we> by friction1 is made ( wood4 ,! ends o o ( ! horizontal b> e1 are def5d$ by brass tubes work+ 9 mahogany1 & h ev5 n[ b little %ake1 ?\gh _m hundr$ ?\s&s ( reciprocations h be5 made4 ,! foot p[] consi/s ( an endless b& ) wood5 treads a a1 pass+ at "o end ( ! app>atus ov] iron :eels b b1 :i* c>ry ! b&-:eel c ^u _! axle4 ,at ! o!r end x goes ov] ! roll]s d d4 ,two pairs ( int]m$iate :eels e e1 s]ve to su/a9 ! weight ( ! man or animal work+ 9 x4 ,! treads are s arrang$ t !y int]lock1 & =m a plat=m1 :i* w n yield d[nw>ds4 ,ow+ to its incl9ation :5 a weight is put on ! plat=m a1 x imm$iately moves f b t[>d d & ! b&-:eel turns4 ,by a mod]ate ex]tion1 equival5t to walk+ up a slight incl9e at a sl[ rate1 a p[] m ?an suffici5t to poli% a #ae-a_/b in* mirror is obta9$4 ,?is ma*9e1 9 :i* v little =ce is lo/ 9 ov]com+ friction1 is frequ5tly employ$ = dairy use1 & is mov$ commonly 9 ! ,/ate ( ,new ,york by a %eep4 ,i h g5]ally myself walk$ 9 ! "o us$ by me1 & h travell$ "s days1 dur+ five h\rs1 m ?an t5 miles4 ,9 ord] to give an idea ( ! me?od ( us+ a gr9d+ & poli%+ ma*9e1 ! foll[+ extract f ! work%op note-book is introduc$3-- 8,a disk ( plate glass #ae-a_/b in*es 9 diamet]1 & #a-a_/d in* ?ick 0 procur$4 ,x _h be5 poli%$ flat on bo? sides1 s t its int]nal con/itution might be se54#d ,x 0 fa/5$ ^u ! table b ( ! ma*9e1 by f\r blocks ( wood z at c1 ,fig4 #ba4 ,und]nea? ! glass 7 ?ree ?ick folds ( blanket1 #ae in*es 9 diamet]1 to prev5t scrat*+ ( ! l[] face1 & avoid risk ( fracture4 ,a convex disk ( lead weigh+ #dj p\nds hav+ be5 ca/1 0 laid ^u ! upp] surface ( ! glass1 & !n ! screw l 0 depress$ s z to cat* 9 a p]=at$ iron plate n1 at ! back ( ! lead m1 & press d[nw>d /rongly4 #d ,! glass t ,i h us$ has g5]ally be5 su* z 0 int5d$ = dead-lights & sky-lights 9 %ips4 8,em]y z co>se z ! head ( a p9 hav+ be5 introduc$1 ?r\gh a hole 9 ! lead1 motion 0 comm5c$ & cont9u$ = half an h\r1 an occasional supply ( em]y be+ giv54 ,! ma*9e made #aej eight-in* cross /rokes1 & ! mirror #ej revolutions p] m9ute4 ,! gr9d] m 0 occasionally re/ra9$ f turn+ by ! h&4 ,at ! end ( ! "t ! detritus 0 wa%$ away1 & an exam9ation ) ! gauge made4 ,a spot #aa in*es 9 diamet]1 & #a_/fj ( an in* deep1 0 f\nd to h be5 gr\nd out4 ,! same process 0 cont9u$ at int]vals = t5 h\rs1 measurem5ts ) ! gauge be+ frequ5tly made4 ,! concave 0 !n suffici5tly deep4 ,! lead5 gr9d] 0 kept ( ! "r convexity by beat+ x on ! back :5 necess>y4 ,a f9] v>iety ( co>se em]y1 & aft] t fl\r em]y 7 next put on1 ea* = an h\r4 ,^! left ! surface mod]ately smoo?1 & ne>ly ( ! "r focal l5g?4 ,! lead5 gr9d] 0 !n dismiss$1 & ! iron "o1 ,fig4 #f1 put 9 its /ead4 ,! mirror 0 remov$ f its place1 & gr\nd ^u a l>ge piece ( flat glass = t5 m9utes1 to produce a circul> outl9e to ! concavity4 ,x 0 cem5t$ ) s(t pit* to ! concave iron disk1 ! c\nt]p>t ( ,fig4 #f1 & aga9 rec5tr$ on ! blanket$ table b4 ,em]ies ( #c & #bj seconds1 & #a1 #c1 #aj1 #cj1 #fj m9utes' elutriation 7 work$ on x1 an h\r ea*4 ,! rate ( cross motion 0 r$uc$ to #be p] m9ute to avoid heat+1 ! mirror /ill revolv+ once = e ?ree cross /rokes4 ,! screw pressure ( l 0 /opp$4 ,?is produc$ a surface exquisitely f9e1 semi-transp>5t1 & appe>+ z if cov]$ ) a ?9 film ( dri$ milk4 ,x c\ld reflect ! light f objects outside ! w9d[ until an incid5ce ( #de degrees 0 rea*$1 & at night 0 f\nd to be bright en\gh = a prelim9>y exam9ation at ! c5tre ( curvature4 8,! poli%] 0 con/ruct$ 9 ! usual way 7page #ab71 & be+ sme>$ ) r\ge 0 fa/5$ to ! table b1 :]e ! mirror _h be54 ,! latt] w>m$ 9 wat] to #abj ,f41 0 !n put face d[nw>ds ^u ! =m]1 & ! screw l s l[]$ z to cause no pressure4 ,! ma*9e 0 all[$ to make #bj f\r-in* cross /rokes p] m9ute1 & ! poli%] to revolve once = e ?ree /rokes4 ,! mirror be+ uncon/ra9$ly support$ on ! poli%]1 0 irregul>ly rotat$ by h&1 or r prev5t$ f rotat+ ) ! poli%]4 ,! t5d5cy ( ?is me?od is to produce an almo/ sph]ical surface4 ,to *ange x to a p>aboloid1 x 0 only necess>y :5 ! glass 0 poli%$ all ov] to increase ! l5g? ( ! /roke to #h in*es1 & cont9ue work+ fifte5 m9utes at a "t1 exam9+ 9 ! int]vals by ! te/s at ! c5tre ( curvature4 ,! production ( a poli% all ov] occupi$ ab\t two h\rs1 b ! correction ( figure took m "t1 on acc\nt ( ! frequ5t exam9ations1 & ! absolute necessity ( all[+ ! mirror to come back to a /ate ( equilibrium f :i* x _h be5 di/urb$ :5 work$ on ! ma*9e40 ,i h se5 a mirror :i* 0 p>abolic :5 j (f ! ma*9e1 by cool+ ov] night become sph]ical4 ,& ^! heat *anges are (t5 succe$$ by o!r sl[] molecul> movem5ts1 :i* cont9ue to modify a surface = _m days aft]4 ,?is correction1 :]e "t & n l5g? ( /roke is ! gov]n+ ag5t1 has once or twice be5 accompli%$ 9 fifte5 m9utes1 b sometimes has co/ sev]al h\rs4 ,if ! figure %\ld h become a hyp]boloid ( revolution1 t is1 h its edge zones too long 9 comp>ison ) ! c5tre1 x is only necess>y to %ort5 ! /roke to br+ x back to ! sph]e1 or ev5 to ov]pass t & produce a surface 9 :i* at ! c5tre ( curvature ! edge zones h too %ort a focal l5g? 7,fig4 #ab74 ,v mu* less tr\ble f zones ( unequal focal l5g? 0 exp]i5c$ aft] ?is ma*9e & sy/em ( work+ 7 adopt$4 ,?is 0 ow+ probably p>tly to ! elem5t ( irregul>ity 9 ! rotation ( ! mirror1 & p>tly to ! fact t ! surface is kept sph]ical until poli%$1 & is !n rapidly *ang$ to ! p>aboloid4 ,:]e ! adju/m5ts ( an app>atus are made s z to attempt to keep a surface p>abolic = "s h\rs1 !re is a /rong t5d5cy = zones to appe>1 & ( a wid? be>+ a fix$ relation to ! /roke4 ,! me?od ( produc+ reflect+ surfaces next to be spok5 (1 is h[ev] t :i* has f9ally be5 adopt$ z ! be/ ( all1 be+ capable ( =m+ mirrors :i* are z p]fect z c be1 & yet only requir+ a %ort "t4 ,x is ! correction ( a surface by local ret\*es4 ,9 ! acc\nt publi%$ by ,m4 ,f\cault1 x appe>s t he is 9 ,france ! inv5tor ( ?is improvem5t4 ,! mode ( practis+ ! ret\*es is z foll[s3 ,sev]al disks ( wood1 z a1 ,fig4 #bc1 v>y+ f #h in*es to #a_/b an in* 9 diamet]1 are to be provid$1 & cov]$ ) pit* or ros9 ( ! usual h>dness1 9 squ>es z at c1 on "o side4#e ,on ! o!r a l[ cyl9drical h&le b1 is to be fix$4 ,! mirror a1 ,fig4 #bd1 hav+ be5 f9$ ) ! succession ( em]ies be=e describ$1 is laid face upw>d on sev]al folds ( blanket1 arrang$ ^u a circul> table1 screw$ to an isolat$ po/ 9 ! c5tre ( ! ap>tm5t1 :i* p]mits ! op]ator to move completely r\nd x4 ,an ord9>y b>rel has g5]ally suppli$ ! place ( ! po/1 ! head c1 ,fig4 #bd1 s]v+ = ! circul> table1 & ! rim b prev5t+ ! mirror slid+ (f4 ,! o!r end is fa/5$ to ! floor by f\r cleets d d4 #e ,m4 ,f\cault us$ plano-convex l5ses ( glass1 ( a radius ( curvature slightly less ?an t ( ! mirror1 & cov]$ ) pap] on ! convex face4 ,illu/ration3 ,fig4 #bc4 ,local ,poli%]4 ,illu/ration3 ,fig4 #bd4 ,section ( ,optician's ,po/4 ,! l>ge poli%] is fir/ mov$ ov] ! surface 9 /raight /rokes ^u e *ord1 & a mod]ate pressure is ex]t$4 ,z soon z ! mirror is at all bright5$1 p]haps 9 five m9utes1 ! op]ation is to be susp5d$1 & an exam9ation at ! c5tre ( curvature made4 ,by c>efully turn+ r\nd1 ! be/ diamet] = support is to be f\nd1 & m>k$ ) a rat-tail file on ! edge1 & !n ! curve ( ! mirror asc]ta9$4 ,if x is ne>ly sph]ical1 z w be ! case if ! gr9d+ has be5 conduct$ ) c>e & irregul> heat+ avoid$1 x is to be replac$ on ! blanket$ support1 & ! previ\s action kept up until a f9e poli%1 free f dots l /ippl+1 is atta9$4 ,?is /age %\ld occupy ?ree or f\r h\rs4 ,ano!r exam9ation %\ld reveal ! same appe>ances z ! prec$+4 ,x is next necess>y to l5g!n ! radius ( curvature ( ! edge zones1 or :at is mu* bett] %ort5 t ( ! c5tre1 s z to conv]t ! section curve into a p>abola4 ,?is is accompli%$ by /raight /rokes across e diamet] ( ! face1 at fir/ ) a #d in*1 !n ) a #f in*1 & f9ally ) ! #h in* poli%]4 ,exam9ations mu/1 h[ev]1 be made e five or t5 m9utes1 to det]m9e h[ mu* lat]al dep>ture f a direct diametrical /roke is necess>y1 to r5d] ! curve uni=m out to ! edge4 ,c>e mu/ be tak5 always to w>m ! poli%]1 ei!r 9 front ( a fire or ov] a _s lamp1 be=e us+ x4 ,p]haps ! mo/ /rik+ feature 9 ?is op]ation is t ! mirror pres5ts cont9ually a curve ( revolution1 & is n div]sifi$ ) undulations l a ruffle4 ,by walk+ /eadily r\nd ! support1 on ! top ( :i* ! mirror is plac$1 !re seems to be no t5d5cy = su* irregul>ities to arise4 ,if ! correction = sph]ical ab]ration %\ld h proce$$ too f>1 & ! mirror become hyp]bolic1 ! sph]e c be recov]$ by work+ a succession ( poli%]s ( increas+ size on ! zone a1 ,fig4 #af1 int]m$iate betwe5 ! c5tre & edge1 caus+ _! c5tres to pass along e *ord t c be describ$ tang5t to ! zone4 ,a mo/ p]fect & rapid control c ?us be ex]cis$ ov] a surface1 & an uni=m result v quickly atta9$4 ,x becomes a pleasant & int]e/+ occupation to produce a mirror4 ,b two effects h pres5t$ !mselves 9 ?is op]ation1 :i* un=tunately b> ! way to ! v be/ results4 ,9 ! fir/ place ! edge p>ts ( su* mirrors1 = m ?an half an in* all ar\nd1 b5d backw>ds & become ( too great focal l5g?1 & ! rays f ^! p>ts _c be unit$ ) ! re/ =m+ ! image4 ,9 ! second place1 ! surface1 :5 critically exam9$ by ! second te/1 is f\nd to h a delicate wavy or fleecy appe>ance1 n se5 9 ma*9e poli%+4#f ,al?\gh ! v>iations f ! true curve impli$ by ^! latt] greatly exagg]at$ imp]fections are exce$+ly small1 & d n prev5t a !rmomet] bulb 9 ! sun%9e appe>+ l a disk surr\nd$ by r+s ( int]f]5ce1 yet !y mu/ div]t "s undulations f _! prop] direction1 or else !y w\ld n be visible4 ,all k9ds ( /rokes h be5 tri$1 /raight1 sweep+ circul>1 hypocycloidal1 c4 )\t effect+ _! removal4 ,m4 ,f\cault1 :o us$ a pap] poli%]1 also enc\nt]$ !m4 ,ev5tually !y 7 imput$ to ! unequal pressure ( ! h&1 & 9 consequ5ce a ma*9e to ov]come ! two above m5tion$ faults ( manual correction 0 con/ruct$4 #f ,by ?is x is n meant t !re is a rippl$ poli%1 l t produc$ by bucksk94 ,illu/ration3 ,fig4 #be4 ,ma*9e = ,local ,corrections4 ,! mirror a1 is c>ri$ by an iron *uck or table b1 cov]$ ) a triple fold ( blanket1 & is prev5t$ f slipp+ (f by f\r cleets c c4 ,! v]tical %aft d passes ?r\gh a worm-:eel e1 ! endless screw ( :i* f1 is driv5 by a b& g1 f ! prim>y %aft h4 ,at i is ! b&-:eel = connection to ! foot-p[]4 ,at "o end ( ! prim>y %aft is firmly fix$ ! cog:eel k1 :i* drives ! crank-%aft l4 ,atta*$ to ! horizontal "p ( l1 is ! crank-p9 m4 ,! two bolts n n move 9 a slot1 s t ! crank-p9 may be set at any di/ance f #j to #b in*es1 out ( l9e ) l4 ,above1 ! crank-p9 c>ries "o end ( ! b> o1 ! o!r end pass+ ?r\gh an elliptical hole 9 ! oak-block p4 ,d[n ! middle ( ! b> runs a long slot1 ?r\gh :i* ! screw-p9 q passes1 & :i* p]mits q to be br\ght ov] any zone f ! c5tre to ! edge ( ! mirror a4 ,x is reta9$ by ! bolts r r1 :i* are tapp$ into s4 ,! local poli%] is se5 at t4 ,! curve :i* ! c5tre ( ! local poli%] describes ^u ! face ( ! mirror1 v>ies ) ! adju/m5ts4 ,fig4 #bf is a r$uction f "o trac$ by ! ma*9e1 ! ov]lapp+ be+ se5 on ! left side4 ,! mirror is n tightly conf9$ by ! cleets c c1 = t w\ld c]ta9ly injure ! figure1 b p]=ms a sl[ motion ( rotation1 s t 9 no two successive /rokes are ! same p>ts ( ! edge press$ aga9/ !m4 ,illu/ration3 ,fig4 #bf4 ,hypocycloidal ,curve4 ,! local poli%]s are made ( lead1 alloy$ ) a small proportion ( antimony1 & are #h1 #f1 & #d in*es 9 diamet]1 respectively4 ,! l>ge/ & smalle/ are mo/ us$1 ! =m] on acc\nt ( its size poli%+ mo/ quickly1 b ! latt] giv+ ! true/ surface4 ,! ros9 t cov]s !m is j ind5table by ! ?umb nail1 & is arrang$ 9 a novel mann]4 ,! lead5 basis1 z se5 at t1 ,fig4 #be1 is p]=at$ 9 _m places ) holes1 :i* p]mit evaporation1 s]ve = ! introduction ( wat] :]e ne$$1 & all[ ! ros9 to spread freely4 ,grooves are made f "o ap]ture to ano!r1 & ! ros9 ?us divid$ into irregul> portions4 ,! effects ( ! production ( heat are 9 ?is way avoid$4 ,! mirror may be gr\nd & f9$ on ?is ma*9e1 9 ! same mann] z on t describ$ at page #ba1 or x may be gr\nd ) a small tool #h in*es 9 diamet]1 z rec5tly sugge/$ by ,m4 ,f\cault1 ! results 9 ! latt] case be+ j z good a surface ( revolution z 9 ! =m]4 ,x is be/ poli%$ ) ! #h in*1 & a mod]ate pressure may be giv5 by ! screw q1 if ! pit* is n too s(t4 ,?is1 h[ev]1 t5ds to leave an excavat$ place at ! c5tre ( ! mirror1 ! size dep5d+ on ! /roke ( ! crank m1 :i* %\ld be ab\t #b in*es4 ,! p9 q ought to be half way f ! c5tre to ! edge ( ! mirror1 b mu/ be occasionally mov$ "r or left an in* along ! slot4 ,:5 ! surface is approa*+ a p]fect poli%1 ! w>m$ #d in* poli%] mu/ be put 9 ! place ( ! #h in*4 ,! p9 q mu/ be set exactly half-way betwe5 ! c5tre & edge ( ! mirror1 & ! crank mu/ h a /roke ( two in*es radius4 ,! poli%] !n j goes up to ! c5tre ( ! glass surface ) "o edge1 & to ! p]iph]y ) ! o!r1 :ile ! out] excursion ( ! inn] edge & inn] excursion ( ! out] edge meet1 & neutralize "o ano!r at a midway po9t4 ,:]ev] ! edge ( a poli%] *anges direction _m times 9 succession1 on a surface1 a zone is sure to =m1 unless avoid$ 9 ?is mann]4 ,all ! =ego+ description is = a #ae-a_/b in* mirror4 ,by ?is sy/em ( local poli%+ ! difficulties ( heat1 di/ribution ( poli%+ p[d]s1 irregul> contact ( ! ros91 c4 t r5d] ! atta9m5t ( a f9e figure s unc]ta9 usually1 entirely disappe>4 ,a sph]ical surface is produc$ z above describ$1 & aft]w>ds by mov+ q t[>ds ! edge1 & at ! same "t increas+ ! /roke1 x is conv]t$ into a p>aboloid4 ,! fleecy appe>ance spok5 ( on a =m] page is n p]ceiv$1 & ! surface is good almo/ up to ! extreme edge4 7#d47 ,,eye-,,pieces1 ,,plane ,,mirrors ,,& ,,te/ ,,objects4 ,! telescope is furni%$ ) sev]al eye-pieces ( v>i\s con/ruction1 giv+ magnify+ p[]s f #ge to #abjj1 or if x 7 desir$ ev5 high]4 ,= ! m$ium p[]s #cjj & #fjj ,ramsd51 or r positive eye-pieces h be5 adopt$4 ,!y diff]1 h[ev]1 f ! usual =m 9 be+ a*romatic1 t is1 ea* plano-convex is compos$ ( a fl9t & cr[n1 arrang$ accord+ to =mulas calculat$ by ,littr[4 ,9 ?is way a l>ge flat field & abs5ce ( color are secur$1 & ! f9e images yield$ by ! mirror are n injur$4 ,= ! high] p[]s1 s+le a*romatic l5ses are us$1 & = ! highe/ ( all a ,ross microscope4 ,) ^! means x has be5 f\nd t ! p>abolic surfaces yield$ by ! processes be=e describ$1 w def9e te/ objects excell5tly4 ,( close d\ble />s !y w sep>ate su* z #b ,&rom$1 & %[ ! colors ( ! compon5ts4 ,9 ! case ( unequal />s :i* seem to be m sev]e te/s1 !y c %[ ! close companion ( ,sirius--discov]$ by ,mr4 ,alvan ,cl>k's magnific5t refractor--! six? compon5t ( #a ,orionis1 & a multitude ( o!r difficult objects4 ,z an example ( light collect+ p[]1 ,debillisima betwe5 & #e ,lyr is f\nd to be qu9tuple1 z fir/ notic$ by ,mr4 ,lassell4 ,9 ! #ah-a_/b in* specula ( ,h]s*el1 x 0 only record$ z d\ble1 &1 accord+ to ,admiral ,smy?1 ,"l ,rosse did n notice ! f\r? & fif? compon5ts4 ,jupit]'s moons %[ ) beautiful disks1 & _! diff]5ce 9 diamet] is v m>k$4 ,z = ! body ( t planet1 x is lit]ally cov]$ ) belts up to ! poles4 ,! bright & d>k spots on ,v5us1 & ! fad+ illum9ation ( h] inn] edge1 & its irregul>ities are p]ceiv$ ev5 :5 ! air is f> f tranquil4 ,/>s are (t5 se5 z disks1 & )\t any w+s or tails1 unless inde$ ! mirror %\ld be wrongly plac$1 s t ! be/ diamet] = support is n 9 ! p]p5dicul> plane1 pass+ ?r\gh ! axis ( ! tube4 ,x has be5 f\nd t no advantage o!r ?an ! decrease ( atmosph]ic influ5ce on ! image1 results f cutt+ d[n ! ap]ture ( ^! mirrors by diaphragms1 :ile ! disadvantage ( r$uc+ ! sep>at+ p[]1 is p]ceiv$ at ! same "t4 ,fa9t objects c be bett] se5 ) ! :ole surface ?an ) a r$uc$ ap]ture1 & ?is ?\gh app>5tly a prop]ty common to all reflectors & object glasses is n s 9 reality4 ,a defective edge w (t5 cause ! :ole field to be fill$ ) a pale milky light1 :i* w ext+ui% ! fa9t] />s4 ,good def9ition is j z important = fa9t z = close objects4 ,! prop]ties ( ^! mirrors h be5 be/ %[n by ! excell5ce ( ! photographs tak5 ) !m4 ,al?\gh ^! are n z %>p z ! image se5 9 ! telescope1 yet x mu/ n be suppos$ t an imp]fect mirror w give j z good pictures4 ,a photograph :i* is magnifi$ to #c feet1 repres5ts a p[] ( #chj4 ,z ! orig9al negative tak5 at ! focus ( ! mirror is n q #a-a_/b in* 9 diamet] :5 ! moon is at its mean di/ance1 x has to be enl>g$ ab\t #be times1 & has !re=e to be v %>p to be> x4 ,! light collect+ p[] ( an unsilv]$ mirror is q surpris+4 ,) a #ae-a_/b in*1 ! companion ( ,lyr c be p]ceiv$1 ?\gh x is only ( ! elev5? magnitude4 ,! moon & o!r bright objects are se5 ) a purity highly pleas+ to ! eye1 "s p>ts be+ ev5 m visible ?an aft] silv]+4 ,9 ord] to f9i% ?is description1 "o "p m ( ! optical app>atus requires to be notic$--! plane mirrors4 ,9 ! ,newtonian reflector ! image is reject$ out at ! side ( ! tube by a flat surface plac$ at #de ) ! optical axis ( ! l>ge concave4#g ,if ?is second>y mirror is ei!r convex or concave1 x modifies ! image injuri\sly1 caus+ a /> to look l a cross1 & ?is ?\gh ! curvature be s slight z h>dly to be p]ceptible by ord9>y means4 ,= a long "t ,i us$ a piece #c #e in*es1 :i* 0 cut f ! c5tre ( a l>ge look+-glass accid5tally brok51 b ev5tually f\nd t by gr9d+ ?ree pieces ( #f in*es 9 diamet] aga9/ "o ano!r1 & poli%+ !m on v h>d pit*1 a ne>] approa* to a true plane c\ld be made4 ,!y 7 te/$ by be+ put 9 ! telescope1 & obs]v+ :e!r ! focus 0 l5g!n$ or %ort5$1 & also by trial on a />4 ,:5 suffici5tly good to be> ^! te/s1 a piece ( ! "r size 0 cut out ) a diamond1 f ! c5tral p>ts4 #g ,a "r-angl$ prism _c be us$ ) advantage to replace ! plane silv]$ mirrors1 because x transmits less light ?an !y reflect1 is m liable to injure ! image1 & ! glass is apt to be m or less color$4 ,its great size & co/1 "o ?ree in*es squ>e on two faces be+ requir$ = my purposes1 has also to be consid]$4 #b4 ,,! ,,telescope ,,m\nt+4 ,! telescope is m\nt$ z an altitude & azimu? in/rum5t1 b 9 a mann] t causes x to diff] f ! usual in/rum5t ( t k9d4 ,! ess5tial feature is1 t ! eye-piece or place ( ! s5sitive plate is /ation>y at all altitudes1 ! obs]v] always look+ /raight =w>d1 & nev] hav+ to /oop or assume inconv5i5t & con/ra9$ positions4 ,illu/ration3 ,fig4 #bg4 ,miss ,h]s*el's ,telescope4 ,! /ation>y eye-piece m\nt+ 0 fir/ us$ by ,miss ,c>ol9e ,h]s*el1 :o _h a #bg in* ,newtonian arrang$ on t plan4 ,fig4 #bg4 7,smy?'s ,cele/ial ,cycle47 ,subsequ5tly x 0 appli$ to a l>ge telescope by ,mr4 ,nasmy?1 ! em95t eng9e]1 b no details ( 8 con/ruction h rea*$ me4 ,he us$ x = mak+ draw+s ( ! moon1 :i* are said to be excell5tly execut$4 ,:5 x became necess>y to det]m9e h[ my telescope %\ld be m\nt$1 ,i 0 /rongly urg$ to make x an equatorial4 ,b aft] reflect+ on ! fact t x 0 int5d$ = photography1 & t absolute fre$om f tremor 0 ess5tial1 a condition n atta9$ 9 ! equatorial :5 driv5 by a clock1 & 9 addition t 9 ! case ( ! moon rotation ^u a pol> axis does n suffice to c\nt]act ! motion 9 decl9ation1 ,i 0 l$ to adopt ! o!r =m4 ,a great _m modifications ( ! orig9al idea h be5 made4 ,= in/ance1 in/ead ( c\nt]pois+ ! end ( ! tube conta9+ ! mirror by ext5d+ ! tube to a di/ance beyond ! altitude or horizontal axis1 ,i introduc$ a sy/em ( c\nt]poise lev]s :i* all[s ! telescope to "w 9 a space little m ?an its own focal l5g? across4 ,?is con/ruction p]mits bo? ends ( ! tube to be support$1 ! l[] "o on a wire rope1 & gives ! greate/ fre$om f tremor1 ! p>ts com+ quickly to re/ aft] a movem5t4 ,9 ! use ( ! telescope = photography1 z we %all see1 ! sy/em ( br++ ! mass ( ! in/rum5t to complete re/ be=e expos+ ! s5sitive plate1 & only driv+ t plate itself by a clock1 is always adopt$4 ,! obvi\s disadvantage connect$ ) ! alt-azimu? m\nt+--! difficulty ( f9d+ "s objects--has n be5 a s\rce ( emb>rassm5t4 ,9 fact ! in/ability ( ! optical axis 9 reflect+ in/rum5ts1 if ! mirror is uncon/ra9$ly support$1 z x %\ld be1 r5d]s !m unsuitable = det]m9ations ( position4 ,a little pati5ce w enable an obs]v] to f9d all necess>y te/s1 or curi\s objects4 ,! m\nt+ is divid$ into3 a4 ,! ,tube2 & b4 ,! support+ frame4 a4 ,! ,tube4 ,! telescope tube is a sixte5 sid$ prism ( walnut wood1 #ah in*es 9 diamet]1 & #ab feet long4 ,! /aves are #c_/h ( an in* ?ick1 & are hoop$ toge!r ) f\r b&s ( brass1 capable ( be+ tight5$ by screws4 ,inside ! tube are plac$ two r+s ( iron1 half an in* ?ick1 r$uc+ ! int]nal diamet] to ab\t #af in*es4 ,at opposite sides ( ! upp] end ( ! tube are screw$ ! p]=at$ trunnions a1 ,fig4 #bh 7( :i* only "o is %[n71 ^u :i* x sw+s4 ,surr\nd+ ! o!r end is a wire rope b b b1 ! ends ( :i* g ov] ! pulleys c 7c n %[n7 on friction roll]s1 & t]m9ate 9 disks ( lead d d4 ,^! c\nt]poises are fa/5$ on ! ends ( lev]s e e1 :i* turn bel[ on a fix$ axle f4 ,by ?is arrangem5t z ! tube assumes a horizontal position & becomes1 s to speak1 heavi]1 ! c\nt]poises d ! same1 :ile :5 ! tube becomes p]p5dicul>1 & mo/ ( its weight falls ^u ! trunnions1 ! c\nt]poises are c>ri$ mo/ly by _! axle4 ,a cont9ual condition ( equilibrium is ?us rea*$1 ! tube be+ easily rais$ or depress$ to any altitude desir$4 ,x is necess>y1 h[ev]1 to con/ra9 ! wire rope b b b1 to move 9 ! arc ( ! circle describ$ by ! end ( ! tube & ends ( ! lev]s & h5ce ! twelve roll]s or guide pulleys g g g4 ,ov] "s ( ! same pulleys a ?9 wire rope h h runs1 b :ile its ends are fa/5$ to ! l[] "p ( ! tube at b1 ! c5tral p>ts g twice ar\nd a roll] connect$ ) ! w9* i1 ne> ! eye-piece1 ?us enabl+ ! obs]v] to move ! telescope 9 altitude1 )\t tak+ ! eye f ! eye-piece4 ,illu/ration3 ,fig4 #bh4 ,sectional ,view ( ,obs]vatory4 ,! iron wire rope requir$ to be c>efully made1 s z to avoid rigidity4 ,x conta9s #b-a_/c miles ( wire1 #a_/ajj ( an in* 9 diamet]1 & has #cjj /r&s4 ,ea* s+le wire w support #g p\nds4 ,x is1 h[ev]1 m flexible ?an a hemp5 rope ( ! same size1 ow+ to its loose twi/+4 ,illu/ration3 ,fig4 #bi4 ,! ,mirror ,support4 ,at ! l[] end ( ! tube1 at ! di/ance ( a foot1 & cross+ x at "r angles1 held by ?ree b>s ( iron i i i1 ,fig4 #bi1 is a circul> table ( oak e1 :i* c>ries an ,india-rubb] air sac d1 & ^u ?is ! mirror f is plac$4 ,! edge support ( ! mirror is furni%$ by a semicircul> b& ( t9-plate a1 l9$ inside ) cotton1 & fa/5$ at ! ends by l9ks ( *a9 b1 7b n se57 to two screws c c2 g & h are ! wire ropes1 m>k$ b & h 9 ,fig4 #bh4 ,in/ead ( ! blanket support :i* ,h]s*el f\nd s advantage\s1 ,m4 ,f\cault has sugge/$ ?is use ( an air sac4 ,9 8 in/rum5t !re is a tube go+ up to ! obs]v]1 by :i* he may adju/ its degree ( inflation4 ,x requires t !re %\ld be ?ree be>+s c c c1 9 front ( ! mirror1 aga9/ :i* x may press :5 ! sac beh9d is inflat$1 o!rwise ! optical axis is altoge!r too in/able1 & objects _c be f\nd4 ,! arrangem5t c]ta9ly gives beautiful def9ition1 br++ />s to a disk :5 ! glass j floats1 )\t t\*+ its front be>+s4 ,! fir/ sac t ,i made 0 compos$ ( two circul> %eets ( ,india-rubb] clo?1 jo9$ ar\nd ! edges4 ,b ?is c\ld n be us$ :ile photograph+1 because ! image 0 kept 9 a /ate ( cont9u\s oscillation if !re 0 a breeze1 & ev5 "u m favorable circum/ances took a long "t to come to re/4 ,x 0 n advisable to bl[ ! mirror h>d up aga9/ its ?ree front be>+s1 9 ord] to avoid ! in/ability1 = !n e po9t 9 ( an object became triple4 ,to ! eye ! oscillations 7 n (f5sive1 because ! sway+ image 0 %>p4 ,subsequ5tly1 h[ev]1 an air *air cu%ion 0 procur$1 & z ! surface 0 flat in/ead ( convex ! difficulty became s mu* less1 t ! blanket support 0 def9itely ab&on$4 ,x is necess>y t ! mirror %\ld h free play 9 ! direction ( ! l5g? ( ! tube :5 ?is k9d ( support is us$1 & t is ! reason :y ! t9 edge hoop mu/ t]m9ate 9 l9ks ( *a94 ,! int]val1 eight or t5 in*es1 :i* sep>ates ! face ( ! mirror f ! tube1 is occupi$ by a curta9 ( black velvet1 conf9$ bel[ by a draw+ cord & tack$ above to ! tube4 ,?is p]mits access to ! mirror to put a glass cov] on x1 & :5 %ut d[n /ops ! curr5t ( air ru%+ up4 ,:5 ! in/rum5t is n be+ us$ ?is curta9 is left op51 because ! mirror & tube are 9 t case kept m uni=m 9 temp]ature ) ! surr\nd+ air4 ,9 spite ( su* contrivances !re is /ill sometimes a /rong residual curr5t 9 ! tube4 ,i h tri$ to ov]come x by cov]+ ! m\? ( ! tube ) a %eet ( flat glass1 b h be5 oblig$ to ab&on t because ! images 7 injur$4 ,at "o "t1 too1 :5 x 0 suppos$ t ! curr5t 0 p>tly f ! obs]v]'s body1 heat$ /reams ( air go+ out ar\nd ! tube1 ! ap]ture 9 ! dome 0 clos$ by a conical bag ( musl91 :i* fitt$ ! m\? ( ! telescope tightly4 ,! only advantages result+ 7 m]e bodily com=t & a capability ( p]ceiv+ fa9t] objects ?an be=e1 because ! sky-light 0 %ut (f4 ,illu/ration3 ,fig4 #cj4 ,section ( ,azimu? ,axis4 b4 ,! ,support+ ,frame4 ,! frame :i* c>ries ! prec$+ p>ts is ( wood1 & re/s on a v]tical axis a1 ,fig4 #cj1 turn+ bel[ 9 a gun-metal cup b1 support$ by a m>ble block re/+ on ! solid rock4 ,! upp] end ( ! axis is su/a9$ by two coll>s1 "o c c above1 & ! o!r bel[ an int]m$iate triangul> box e e f ! sides ( :i* ?ree long beams f f f #ab #c in*es div]ge1 gradually decl9+ till !y meet ! solid rock at ! limits ( ! excavation 9 :i* ! obs]vatory is plac$4 ,^! beams are fa/5$ toge!r by cross-pieces g g g1 ,fig4 #ca1 & g ?r\gh ! floor 9 spaces h h h1 s contriv$ t ! floor does n t\* !m4 ,at ! ends !y are cas$ ) a ?ick lead5 %ea?+1 to dead5 vibration & prev5t ! access ( moi/ure4 ,illu/ration3 ,fig4 #ca4 ,plan ( ,obs]vatory 7l[] floor74 ,?is tripod support 9 connection ) ! su/a9+ ( ! telescope by ! wire rope1 gives t /ead9ess :i* is s ess5tial 9 photography4 ,only a slight am\nt ( =ce1 ab\t two p\nds1 is requir$ to move ! in/rum5t 9 azimu?1 ?\gh x weighs almo/ a ?\s& p\nds4 ,! plan ( ! frame c5trally c>ri$ by ! axis a is z foll[s3 ,f ! corn]s ( a p>allelogram i i 7#b #ac feet7 ( wood5 beams1 eight in*es ?ick & ?ree in*es broad1 p]p5dicul>s n n1 ,fig4 #bh1 rise4 ,at ! top !y are connect$ by light] pieces to =m a p>allelogram1 simil> to t bel[1 & j l>ge en\gh to conta9 ! tube ( ! telescope4 ,at "r angles to ! p>allelogram bel[1 & close ^u x1 a brac$ b> o o1 ,fig4 #bh1 crosses4 ,f its extremities f\r slant+ braces z at p p1 ,fig4 #bh1 g to ! corn]s ( ! upp] p>allelogram1 & comb9e to give x lat]al support4 ,at ! top ( "o close pair ( ! p]p5dicul>s n1 ,fig4 #bh1 are bronze frames c>ry+ friction roll]s ^u :i* ! trunnions move1 :ile simil>ly ^u ! o!r pair n are two pulleys1 also on friction roll]s1 = ! wire rope com+ f ! c\nt]poises4 ,movem5t 9 altitude is v easily accompli%$1 & ) ! left h& ^u ! w9* i1 "u high p[]s1 bo? altitude & azimu? motions are controll$1 & ! "r h& left free4 ,! :ole app>atus works s well1 t 9 ord9>y obs]vation ! want ( a clock movem5t has n be5 felt4 ,( c\rse = photography t is ess5tial4 #c4 ,,! ,,clock ,,movem5t4 ,! app>atus = foll[+ cele/ial bodies is divid$ into two p>ts2 a4 ,! ,slid+ ,plate-hold]2 & b4 ,! ,clepsydra4 ,9 addition a %ort description ( ! ,sun-,cam]a1 c1 is necess>y4 a4 ,! ,slid+ ,plate-hold]4 ,mr4 ,de ,la ,rue1 :o has done s mu* = cele/ial photography1 0 ! fir/ to sugge/ photograph+ ! moon on a s5sitive plate1 c>ri$ by a frame mov+ 9 ! app>5t direction ( h] pa?4 ,he nev]1 h[ev]1 appli$ an automatic driv+ me*anism1 b 0 ev5tually l$ to use a clock :i* caus$ ! :ole telescope to revolve ^u a pol> axis1 & ?us comp5sate = ! rotation ( ! e>?1 & on c]ta9 occasions = ! motion ( ! moon h]self4 ,9 ?is way he has produc$ ! be/ results t h be5 obta9$ 9 ,europe4 ,"l ,rosse1 too1 employ$ a simil> slid+ plate-hold]1 b provid$ ) clock-"w to move x at an appropriate rate4 ,i h n be5 able z yet to procure any precise acc\nt ( ei!r ( ^! in/rum5ts4 ,! fir/ photographic repres5tations ( ! moon ev] made1 7 tak5 by my fa!r1 ,pr(essor ,john ,w4 ,drap]1 & a notice ( !m publi%$ 9 8 qu>to "w 8,on ! ,=ces t ,organize ,plants10 & also 9 ! ,septemb] numb]1 #ahdj1 ( ! ,london1 ,ed9burgh1 & ,dubl9 ,philosophical ,magaz9e4 ,he pres5t$ ! specim5s to ! ,new ,york ,lyceum ( ,natural ,hi/ory4 ,! ,secret>y ( t ,association has s5t me ! foll[+ extract f _! m9utes3-- 8,m>* #bc;d1 #ahdj4 ,dr4 ,drap] ann\nc$ t he _h succe$$ 9 gett+ a repres5tation ( ! moon's surface by ! ,dagu]reotype4444 ,! "t occupi$ 0 #bj m9utes1 & ! size ( ! figure ab\t #a in* 9 diamet]4 ,dagu]re _h attempt$ ! same ?+1 b did n succe$4 ,?is is ! fir/ "t t any?+ l a di/9ct repres5tation ( ! moon's surface has be5 obta9$4 8,,robt4 ,h4 ,,br[nne1 ,secret>y40 ,z my fa!r 0 at t "t h[ev] mu* occupi$ ) exp]im5ts on ! ,*emical ,action ( ,light1 ! ,influ5ce ( ,light on ! ,decomposition ( ,c>bonic ,acid by ,plants1 ! ,fix$ ,l9es ( ! ,spectrum1 ,spectrum ,analysis1 c41 ! results ( :i* are to be f\nd scatt]$ ?r\gh ! ,philosophical ,magaz9e1 ,silliman's ,j\rnal1 & ! ,j\rnal ( ! ,frankl9 ,in/itute1 he nev] pursu$ ?is v promis+ subject4 ,"s ( ! pictures 7 tak5 ) a ?ree in*1 & "s ) a five in* l5s1 driv5 by a helio/at4 ,9 #ahej1 ,mr4 ,bond1 tak+ advantage ( ! refractor ( #ae in*es ap]ture at ,cambridge1 obta9$ "s f9e pictures ( ! moon1 & subsequ5tly ( d\ble />s1 m p>ticul>ly ,miz> 9 ,ursa ,major4 ,! driv+ p[]1 9 ?is in/ance1 0 also appli$ to move ! telescope ^u a pol> axis4 ,besides ^!1 sev]al ,engli% & cont95tal obs]v]s1 ,messrs4 ,h>tnup1 ,phillips1 ,crookes1 ,fa!r ,sec*i1 & o!rs1 h work$ at ?is bran* ( a/ronomy1 &1 s9ce #aheg1 ,mr4 ,lewis ,m4 ,ru!rfurd1 ( ,new ,york1 has tak5 _m exquisite lun> photographs1 :i* comp>e favorably ) =eign ones4 ,b 9 none ( ^! in/ances has ! use ( ! slid+ plate-hold] be5 p]si/$ 91 & its advantages br\ght into view4 ,9 ! fir/ place x gets rid completely ( ! difficulties aris+ f ! moon's motion 9 decl9ation1 & 9 ! second1 in/ead ( injur+ ! photograph by ! tremors produc$ 9 mov+ ! :ole heavy mass ( a telescope weigh+ a ton or m1 x only necessitates ! driv+ ( an arrangem5t weigh+ sc>cely an ounce4 ,my fir/ trials 7 ) a frame to conta9 ! s5sitive plate1 held only at ?ree po9ts4 ,two ( ^! 7 at ! ends ( screws to be turn$ by ! h&s1 & ! ?ird 0 on a spr+ s z to ma9ta9 firm contact4 ,?is app>atus work$ well 9 _m respects1 b x 0 f\nd t h[ev] mu* c>e might be tak51 ! h&s always caus$ "s tremor 9 ! in/rum5t4 ,x 0 evid5t !n t ! difficulty f friction :i* besets ! movem5ts ( all su* delicate ma*9]y1 & causes j]k+ & />ts1 w\ld h to be avoid$ 9 "s o!r way4 ,i next con/ruct$ a metal slide to run betwe5 two p>allel /rips1 & gr\nd x into position ) ! greate/ c>e4 ,?is1 :5 set 9 ! direction ( ! moon's app>5t pa?1 & mov$ by "o screw1 work$ bett] ?an ! prec$+4 ,b x 0 soon p]ceiv$ t al?\gh ! /rips fitt$ ! frame z tightly z practicable1 an adhesion ( ! slide took place fir/ to "o /rip & !n to ! o!r1 & a sort ( undulatory or v]micul> progression result$4 ,! am\nt ( deviation f a rectil9e> motion1 ?\gh small1 0 en\gh to injure ! photographs4 ,at ?is /age ( ! inve/igation ! regim5t ( volunte]s to :i* ,i belong$ 0 call$ into active s]vice1 & ,i sp5t sev]al mon?s 9 ,virg9ia4 ,my bro!r1 ,mr4 ,daniel ,drap]1 to ^: me*anical +5uity ,i h on sev]al occasions be5 indebt$ = assi/ance 9 ! manifold difficulties t h aris5 :ile con/ruct+ ?is telescope1 cont9u$ ^! exp]im5ts at int]vals4 ,he pres5t$ me on my return ) a slide & s&-clock1 ) :i* "s excell5t photographs h be5 tak54 ,he _h f\nd t unless ! slide above m5tion$ 0 made ungov]nably long1 ! same tr\ble cont9u$4 ,he !n ceas$ cat*+ ! slid+ frame h1 ,fig4 #cb1 by two opposite sides1 & made x run along a s+le /eel rod a1 be+ atta*$ by means ( two p]=at$ plates ( brass b1 b4 ,! cord i go+ to ! s&-clock1 0 appli$ s z to pull z ne>ly z possible 9 ! direction ( ! rod4 ,a piece ( cork c1 gave ! :ole /ead9ess1 & yet s(tness ( motion4 ,! l[] end ( ! frame 0 prev5t$ f sw++ back & =w>d by a /eel p9 d1 :i* play$ along ! glass rod e4 ,all ^! p>ts 7 atta*$ to a frame k1 fitt+ on ! eyepiece hold]1 & p]mitt+ ! rod a to *ange f ! horizontal position 9 :i* x is "h drawn1 to any angul> "o desir$4 ,! ?umb-screw f reta9$ x 9 place2 g & g are pulleys :i* p]mit ! cord to *ange direction4 ,illu/ration3 ,fig4 #cb4 ,slid+ ,plate-hold]4 ,subsequ5tly1 a bett] me?od ( exam9+ ! uni=mity ( ! rate1 ?an by notic+ ! %>pness ( ! photograph produc$1 0 inv5t$4 ,x consi/s 9 arrang+ a fix$ microscope1 magnify+ ab\t #dj times1 at ! back ( ! gr\nd glass plate1 :i* fits 9 ! same slide z ! s5sitive plate4 ,by wat*+ ! granulat$ appe>ance pass be=e ! eye1 z ! slide is mov$ by ! clock1 ! slighte/ v>iation f uni=mity1 any pulsatile or j]k+ movem5t is r5d]$ visible4 ,by ! aid ( ?is microscopic exagg]ation1 x 0 se5 t occasionally1 :5 !re _h be5 consid]able *anges 9 temp]ature1 ! /ead9ess ( ! motion v>i$4 ,?is 0 trac$ to ! irregul> slipp+ ( b1 b4 ,illu/ration3 ,fig4 #cc4 ,frictionless ,slide 7front view74 ,sectional view4 ,a diff]5t arrangem5t 0 !n adopt$1 by :i* a lun> crat] c be kept bisect$ z long z is necess>y1 & :i* gives orig9 to no irregul>ities1 b pursues a /eady c\rse4 ,! pr9ciple is1 n to all[ a slipp+ friction any:]e1 b to sub/itute roll+ friction1 ^u :eels turn+ on po9ts at ! ends ( _! axles4 ,! foll[+ wood-cut is half ! real size ( ?is arrangem5t4 ,a glass rod a1 a1 ,fig4 #cc1 is su/a9$ by two :eels b1 b1 & kept 9 contact1 ) !m by a ?ird friction roll] c1 press$ d[nw>d by a spr+4 ,?is rod c>ries a circul> frame d1 d1 ^u :i* at e1 e1 e1 are ?ree glass hold]s & plat9um cat*es4 ,a spr+ f holds ! s5sitive plate 9 position1 by press+ aga9/ its back4 ,! circul> frame d is kept 9 "o plane by a f\r? friction roll] g1 :i* runs on a glass rod h1 & is kept aga9/ x by ! inw>d pressure ( ! ov]hang+ frame d4 ,! cord i is atta*$ to ! arm k1 & pulls 9 ! direction ( ! glass rod a4 ,f m to a fix$ po9t ne> b1 a /rip ( ela/ic ,india-rubb] is /ret*$1 to keep ! cord tight4 ,! r+ ( brass n1 n c>ries ! :ole1 s]v+ z a basis = ! /ation>y p>ts1 & 9 its turn be+ fa/5$ to ! eyepiece hold]1 s z to all[ ! glass rod a to *ange direction1 & be br\ght into co9cid5ce ) ! app>5t pa? ( ! moon4 ,at o is a ?umb-screw or clamp4 ,?r\gh ! r+ n1 n1 a groove p is cut1 into :i* a piece ( yell[ glass may be plac$1 :5 ! act9ic rays are to be %ut (f f ! plate4 ,s9ce ?is contrivance has be5 complet$1 all ! previ\s difficulties h vani%$4 ,! mov+ ( a plate c be accompli%$ ) su* precision1 t :5 ! atmosph]e 0 /eady1 negatives 7 tak5 :i* h be5 enl>g$ to ?ree feet 9 diamet]4 ,! l5g? ( "t t su* a slide c be made to run is indef9ite1 dep5d+ 9 my case on ! size ( ! diagonal flat mirror1 & ap]ture ( ! eyepiece hold]4 ,i c foll[ ! moon = ne>ly f\r m9utes1 b h nev] requir$ to d s = m ?an fifty seconds4 ,at ! m\? ( ! in/rum5t1 :]e no second>y mirror is necess>y1 ! "t ( runn+ c\ld be increas$4 ,! sett+ ( ! frictionless slide 9 angul> position is accompli%$ z foll[s3 ,a gr\nd glass plate is put into x1 ) ! gr\nd face t[>d ! mirror4 ,^u ?is face a black l9e mu/ h be5 trac$1 precisely p>allel to ! rod a4 ,?is may be accompli%$ by firmly fix+ a p5cil po9t aga9/ ! gr\nd side1 & !n draw+ ! frame d & glass pa/ x1 :ile ! re/ ( ! slide is held fa/4 ,z ! moon passes across ! field1 ! position ( ! app>atus mu/ be *ang$1 until "o ( ! crat]s runs along ! l9e f end to end4 ,a cross l9e drawn p]p5dicul> to ! o!r1 s]ves to adju/ ! rate ( ! clepsydra z we %all see1 & :5 a crat] is kept /eadily on ! int]section = twice or ?ree times ! "t dem&$ to secure an impression1 ! adju/m5t may be reg>d$ z complete4 ,x is necess>y ( c\rse to expose ! s5sitive plate soon aft]1 or ! app>5t pa? ( ! moon w h *ang$ direction1 unless inde$ ! slide is set to suit a future mom5t4 b4 ,! ,clepsydra4 ,my prime mov] 0 a weight support$ by a column ( s&1 :i*1 :5 ! s& 0 all[$ to run out ?r\gh a v>iable orifice bel[1 c\ld be made to desc5d ) any desir$ velocity & yet ) uni=mity4 ,9 addition1 by ^! means an unlimit$ p[] c\ld be br\ght to be>1 dep5d+ on ! size ( ! weight4 ,previ\sly x 0 propos$ to use wat]1 & comp5sate = ! decrease 9 fl[1 z ! column %ort5$1 by a conical vessel2 b x 0 soon p]ceiv$ t z ea* drop ( wat] escap$ f ! funnel-%ap$ vessel1 only a correspond+ weight w\ld be br\ght into play4 ,?is is n ! case ) s&1 = 9 ?is in/ance e gra9 t passes out causes ! :ole weight t is support$ by ! column to come into action4 ,9 ! =m] in/ance a movem5t consi/+ ( a s]ies ( p]iods ( re/ & p]iods ( motion occurs1 because p[] has to accumulate by float+ weight lagg+ beh9d ! desc5d+ wat]1 & !n sudd5ly ov]tak+ x4 ,9 ! latt] case1 on ! contr>y1 !re is a regul> desc5t1 all m9or resi/ances 9 ! slide be+ ov]come by ! /eady application ( ! :ole mass ( ! weight4 ,:5 ^! advantages 9 ! fl[ ( s& 7 asc]ta9$1 all ! o!r prime mov]s 7 ab&on$4 ,m]cury-clocks1 on ! pr9ciple ( ! hydro/atic p>adox1 air-clocks1 c41 9 great v>iety1 _h be5 con/ruct$4 ,illu/ration3 ,fig4 #cd4 ,! ,s&-,clock4 ,! s&-clock consi/$ ( a tube a 7,fig4 #cd71 eighte5 in*es long & "o & a half 9 diamet]1 ne>ly fill$ ) s& t _h be5 rais$ to a bright r$ heat & sift$4 ,^u ! top ( ! s& a lead5 weight b 0 plac$4 ,at ! bottom ( ! tube a peculi> /opcock1 se5 at 7#b7 enl>g$1 regulat$ ! fl[1 ! am\nt pass+ dep5d+ on ! size ( ! ap]ture d4 ,?is /opcock consi/$ ( two ?9 plates1 fix$ at "o end & free at ! o!r4 ,! "o m>k$ e is ! adju/+ lev]1 & its ap]ture moves pa/ t 9 ! plate g4 ,! lev] f s]ves to turn ! s& (f altoge!r1 )\t di/urb+ ! size ( ! o!r ap]ture1 :i*1 once set to ! moon's rate1 v>ies b slightly 9 %ort times4 ,a movable cov] h1 p]=at$ to all[ ! cord i to pass ?r\gh1 clos$ ! top1 :ile ! vessel k reta9$ ! escap$ s&1 :i* at suitable times 0 return$ into ! tube a1 ! weight b be+ tempor>ily lift$ out4 ,f ! clock ! cord i communicat$ motion to ! frictionless slide1 z %[n 9 ,fig4 #cc4 ,?is cord %\ld be z inela/ic z possible1 consi/5t ) pliability1 & well wax$4 ,"o :o has n inve/igat$ ! matt] w\ld naturally suppose t ! fl[ ( s& 9 su* a long tube w\ld be mu* quick] :5 ! tube 0 full ?an :5 ne>ly empty1 & t c]ta9ly t result w\ld occur :5 a heavy weight 0 put on ! %ift+ mass4 ,b 9 nei!r case h ,i be5 able to detect ! slighte/ v>iation1 =1 al?\gh by %ak+ ! tube a dim9ution ( ! space occupi$ by ! s& may be caus$1 yet no increase ( weight tri$ c\ld accompli% ! same r$uction4 ,^! peculi>ities seem to result f ! s& ar*+ z x 7 across ! vessel1 l %ot 9 a n>r[ tube1 & only yield+ :5 ! "u supports are remov$4 ,9 bla/+1 a heavy *>ge ( gunp[d] c be reta9$ at ! bottom ( a hole1 & made to split l>ge masses ( rock1 by fill+ ! re/ ( ! hole ) dry s&4 ,i believe t no prime mov] is m suitable ?an a s&-clock = purposes :]e /eady motion & a l>ge am\nt ( p[] are dem&$4 ,! simplicity1 = in/ance1 ( a helio/at on ?is plan1 ! l>ge size x might assume1 & its small co/1 w\ld be great recomm5dations4 ,9 ^! respects its advantages ov] :eelwork are v app>5t4 ,! precision ) :i* su* a s&-clock goes may be appreciat$ :5 x is /at$1 t "u a p[] ( #cjj a lun> crat] c be kept bisect$ = _m times ! p]iod requir$ to photograph x4 ,to secure ! greate/ accuracy 9 ! rate ( a s&-clock1 "s precautions mu/ be tak54 ,! tube %\ld be free f d5ts1 ( uni=m diamet]1 & v smoo? or poli%$ inside4 ,wat] mu/ n be p]mitt$ to f9d access to ! s&1 & hygrometric v>ieties ( t sub/ance %\ld be avoid$1 or _! salts wa%$ out4 ,! s& %\ld be burn$ to de/roy organic matt]1 & s sift$ z to reta9 gra9s ne>ly equal 9 size4 ,! weight1 :i* may be ( lead1 mu/ be turn$ s z to g easily d[n ! tube1 & mu/ be cov]$ ) writ+ pap] or "s o!r h>d & smoo? mat]ial1 to avoid ! pron5ess to adhesion ( s&4 ,a long bottle fill$ ) m]cury answ]s well z a sub/itute4 ,i h us$ 9 su* clocks c]ta9 metallic prep>ations3 ,f9e %ot1 on acc\nt ( its equality ( size1 might d = a v l>ge clock ) a consid]able op5+ bel[1 b is unsuitable = a tube ( ! size /at$ above4 ,!re is1 h[ev]1 a me?od by :i* lead c be r$uc$ to a divid$ condition1 l f9e gunp[d]1 :5 x may replace ! s&4 ,if t metal is melt$ ) a little antimony1 & :ile cool+ is %ak5 9 a box conta9+ "s plumbago1 x breaks up at ! in/ant ( solidify+ into a f9e p[d]1 :i* is ab\t five times z heavy z s&4 ,if aft] be+ sift$ to select ! gra9s ( prop] size1 x is all[$ to run ?r\gh a small hole1 ! fl[ is se5 to be entirely diff]5t f t ( s&1 look+ z if a wire or solid rod 7 desc5d+1 & n an aggregation ( p>ticles4 ,x is probable1 !re=e1 t x w\ld d bett] ?an s& = ?is purpose4 ,i h n1 h[ev]1 giv5 x a fair trial1 because j at ! "t :5 ! exp]im5ts ) ! s&-clock _h rea*$ ?is po9t1 ,i det]m9$ to try a clepsydra z a prime mov]4 ,! reason :i* l$ to ?is *ange 0 t x 0 obs]v$ on a c]ta9 occasion :5 ! atmosph]e 0 /eady1 t ! photographs did n correspond 9 %>pness1 be+ 9 fact no bett] ?an on o!r nights :5 !re 0 a consid]able flick]+ motion 9 ! air4 ,a fur!r inve/igation %[$ t 9 ^! columns ( s& !re is apt to be a m9ute vibrat+ movem5t4 ,at ! plate-hold] above ?is is conv]t$ into a s]ies ( arre/s & advances4 ,on "s occasions1 h[ev]1 ^! slight deviations f cont9u\s motion are entirely abs5t1 & g5]ally1 inde$1 !y _c be se51 if ! p>ts ( ! image seem to vibrate on acc\nt ( curr5ts 9 ! air4 ,by ! aid ( ! microscopic exagg]ation describ$ on a =m] page--:i* 0 subsequ5tly put 9 practice--!y may be obs]v$ easily1 if pres5t4 ,:5 ! negative produc$ at ! focus ( ! great mirror is int5d$ to be enl>g$ to two feet or m 9 size1 ^! movem5ts injure x s5sibly4 ,a v>iety ( exp$i5ts 0 resort$ to 9 ord] to avoid !m1 b none prov$ on all occasions successful4 ,x is obvi\s t 9 a wat]-clock1 :]e ! mobility ( ! fluid is s mu* great] ?an t ( solid gra9s1 ?is difficulty w\ld n arise4 ,! foll[+ contrivance 9 :i* ! fault ( ! ord9>y clepsydra1 9 v>y+ rate ( fl[ z ! column %ort5s1 is avoid$1 0 next made4 ,) x ! be/ results are atta9able1 & x seems to be practically p]fect4 ,illu/ration3 ,fig4 #ce4 ,! ,clepsydra4 ,x consi/s ( a cyl9d] a1 9 :i* a pi/on b moves wat]tight4 ,at ! top ( ! pi/on rod is a lead5 five-p\nd weight c1 f :i* ! cord i goes to ! slid+ platehold] g4 ,! l[] end ( ! cyl9d] t]m9ates 9 a /opcock d1 ! h&le ( :i* c>ries a /rong index rod e1 mov+ on a divid$ arc4 ,at f a tube ) a /opcock is atta*$4 ,bel[1 a vessel h receives ! wa/e fluid4 ,9 us+ ! clepsydra ! /opcock ( f is op5$1 & ! pi/on be+ pull$ upw>ds1 ! cyl9d] fills ) wat] f h4 ,! /opcock is !n clos$1 & if d also is %ut1 ! weight w rema9 motionless4 ,! /r+ i is next connect$ ) ! slide1 & ! telescope turn$ on ! moon4 ,z soon z ! slide is adju/$ 9 angul> position 7page #cf7 ! /opcock d is op5$1 until ! weight c moves d[nw>ds1 at a rate t mat*es ! moon's app>5t motion4 ,9 ord] to facilitate ! rat+ ( ! clepsydra1 ! index rod e is press$ by a spr+ k 7#b71 aga9/ an exc5tric l4 ,z ! exc5tric is turn$ r\nd1 ! /opcock d is ( c\rse op5$1 ) great precision & delicacy4 ,! plug ( ?is /opcock 7#c7 is n p]=at$ by a r\nd hole1 b has a slit4 ,?is causes equal movem5ts 9 ! rod e1 to produce equal *anges 9 ! fl[4 ,! rat+ requires consequ5tly only a few mom5ts4 ,! object ( ! side tube f is to avoid di/urb+ d :5 x becomes necess>y to refill ! cyl9d]1 = :5 x is once op5$ to ! "r degree1 x h>dly requires to be t\*$ aga9 dur+ a night's "w4 ,9 ord] to arre/ ! d[nw>d motion ( ! pi/on at any po9t1 a clamp screws on ! pi/on rod1 & c be br\ght into contact ) ! cyl9d] head1 z 9 ! figure4 ,t ?is in/rum5t %\ld op]ate 9 ! be/ mann]1 x is ess5tial to h ! int]ior ( ! brass cyl9d] poli%$ f end to end1 & ( uni=m diamet]4 ,if any irregul>ity %\ld be p]ceiv$ 9 ! rate ( go+1 x c be cur$ completely by tak+ out ! pi/on1 impregnat+ its lea!r /uff+ ) f9e rott5 /one & oil1 & !n rubb+ x up & d[n = five m9utes 9 ! cyl9d]1 s z to re/ore ! poli%4 ,! pi/on & cyl9d] mu/ ( c\rse be wip$1 & regreas$ ) a mixture ( beeswax & olive oil 7equal p>ts7 aft] su* an op]ation4 ,9 replac+ ! pi/on1 ! cyl9d] mu/ be fir/ fill$ ) wat]1 to avoid ! pres5ce ( air1 :i* w\ld act z a spr+4 ,al?\gh x may be object$ t ?is contrivance seems to be v tr\blesome to use1 yet t is n ! case 9 practice4 ,ev5 if x 71 x s f> surpasses any prime mov] t ,i h se51 :]e ! utmo/ accuracy is ne$$1 t x w\ld be well wor? employ+4 c4 ,! ,sun ,cam]a4 ,9 tak+ photographs ( ! sun ) ! full ap]ture ( ?is telescope1 no driv+ me*anism is necess>y4 ,on ! contr>y1 ! difficulty is r to arrange ! app>atus s t an exposure %ort en\gh may be giv5 to ! s5sitive plate1 & sol>ization ( ! picture avoid$4 ,x is n desirable to r$uce ! ap]ture1 = !n ! sep>at+ p[] is less5$4 ,! "t requir$ to obta9 a negative is a v small fraction ( a second1 = ! wavy appe>ance produc$ by atmosph]ic di/urbance is n unfrequ5tly obs]v$ %>ply def9$ 9 ! photograph1 ?\gh ^! a]ial motions are s rapid t !y c sc>cely be c\nt$4 ,"s k9d ( %utt] t c admit & cut (f ! sol> image ) great quickness is !re=e necess>y4 ,illu/ration3 ,fig4 #cf4 ,! ,spr+ ,%utt]4 ,9 front ( an ord9>y cam]a a1 ,fig4 #cf1 atta*$ to ! eyepiece hold] ( ! telescope1 & f :i* ! l5ses h be5 remov$1 a spr+ %utt] is fix$4 ,x consi/s ( a quadrant ( ?9 wood b1 fa/5$ by its "r angle to "o corn] ( ! cam]a4 ,ov] ! hole 9 ?is quadrant a plate ( t9 d c be adju/$1 & held 9 position by a screw mov+ 9 a slot s z to r$uce ! hole if desir$ to a m]e slit4 ,x may v>y f #a-a_/b in* to less ?an #a_/ej ( an in*4 ,! quadrant is drawn d[nw>ds by an ,india-rubb] spr+ g1 #a in* wide1 #a_/h ( an in* ?ick1 & #h in*es long4 ,?is spr+ is /ret*$ :5 9 action to ab\t #ab in*es1 & :5 releas$ draws ! slit pa/ ! ap]ture c 9 ! cam]a4 ,two nicks 9 ! edge ( ! quadrant s]ve ) ! assi/ance ( a p9 e1 :i* c easily be drawn out by a lev] 7n %[n 9 ! cut71 to conf9e ! slit ei!r opposite to or above c4 ,a cat* at f prev5ts ! %utt] recoil+4 ,! s5sitive plate is put inside ! box z usual 9 a plate-hold]4 ,:5 a photograph is tak51 ! spr+ %utt] is drawn up s t ! l[] nick 9 ! edge ( ! quadrant is ent]$ by ! p9 e1 & ! inside ( ! cam]a obscur$4 ,! front slide ( ! platehold] is !n remov$ 9 ! usual mann]1 & ! sol> image be+ br\ght into prop] position by ! aid ( ! telescope f9d]1 ! trigg] reta9+ e is t\*$1 ! %utt] flies pa/ c1 & ! s5sitive plate may !n be remov$ to be develop$4 ,to avoid ! v %ort exposure ne$$ :5 a silv]$ mirror ( #ahh squ>e in*es ( surface is us$1 ,i h tak5 _m sol> photographs ) an unsilv]$ mirror1 :i* only reflects accord+ to ,b\gu] #b-a_/b p] c5t4 ( ! light fall+ ^u x1 & %\ld p]mit an exposure #cg times z long z ! silv]$ mirror4 ,?is is ! fir/ "t t a pla9 glass mirror has be5 us$ = su* a purpose1 al?\gh ,sir ,john ,h]s*el sugge/$ x = obs]vation _m ye>s ago4 ,b ev5tually ?is application ( ! unsilv]$ mirror _h to be ab&on$4 ,x has1 x is true1 ! advantage ( r$uc+ ! light & heat1 b ,i f\nd t ! mom5t ! glass 0 expos$ to ! ,sun1 x comm5c$ to *ange 9 figure1 & alt] 9 focal l5g?4 ,?is latt] difficulty1 :i* sometimes am\nts to half an in*1 r5d]s x well nigh impossible to f9d ! focal plane1 & reta9 x :ile tak+ out ! gr\nd glass1 & putt+ 9 ! s5sitive plate4 ,if ! glass 7 support$ by a r+ ar\nd ! edge1 & ! back left m freely expos$ to ! air1 ! difficulty w\ld be less5$ b n avoid$1 = a glass mirror c be rais$ to #abj ,f4 on a hot day by putt+ x 9 ! sun%9e1 ?\gh only re/+ on a few po9ts4 ,o!r means ( r$uc+ ! light & heat1 dep5d+ on ! same pr9ciple1 c h[ev] be us$4 ,by replac+ ! silv]$ diagonal mirror ) a black glass or pla9 unsilv]$ surface1 z sugge/$ by ,nasmy?1 ! tr\ble s5sibly disappe>s4 ,i h 9 ?is way secur$ n only macul & _! p5umbr1 b also h obta9$ facul almo/ invisible to obs]vation4 ,on "s occasions1 too1 ! precipitate-l or m9ute floccul5t appe>ance on ! ,sun's disk 0 p]ceptible4 ,x seems1 h[ev]1 t ! be/ means ( acquir+ f9e results ) sol> photography1 w\ld be to use ! telescope z a ,cassegra9ian1 & produce an image s mu* enl>g$1 t ! exposure w\ld n h to be conduct$ ) su* rapidity4 ,magnify+ ! image by an eyepiece w\ld 9 a g5]al way h ! same result1 b 9 t case ! photographic advantages ( ! reflector w\ld be lo/1 & x w\ld be no bett] ?an an a*romatic4 #d4 ,,! ,,obs]vatory4 ,?is section is divid$ into a1 ,! ,build+2 b1 ,! ,dome2 & c1 ,! ,obs]v]'s ,*air4 a4 ,! ,build+4 ,! ,obs]vatory is on ! top ( a hill1 #bbe feet above l[ wat] m>k1 & is 9 ,latitude #dj #ei #be nor?1 & ,longitude #gc #eb #be we/ f ,gre5wi*1 accord+ to ! det]m9ations ( ! ,coa/ ,survey4 ,x is ne> ! village ( ,ha/+s-^u-,hudson1 & is ab\t #bj miles nor? ( ! city ( ,new ,york4 ,! surr\nd+ c\ntry on ! banks ( ! ,nor? ,riv] is occupi$ by c\ntry seats1 on ! slopes & summits ( ridges ( l[ hills1 & no (f5sive manufactories vitiate ! atmosph]e ) smoke4 ,our gr\nds are suffici5tly ext5sive to exclude ! ne> passages ( vehicles1 & to avoid tremor & o!r annoyances4 ,illu/ration3 ,fig4 #cg4 ,dr4 ,drap]'s ,obs]vatory4 ,an un9t]rupt$ horizon is comm&$ 9 e direction1 except :]e trees ne> ! dwell+ h\se cut (f a few degrees t[>d ! s\?we/4 ,! advantages ( ! location are v great1 & (t5 :5 ! valleys r\nd are fill$ ) foggy exhalations1 !re is a cle> sky ov] ! ,obs]vatory1 ! mi/ fl[+ d[n l a great /ream1 & los+ itself 9 ! *asm ?r\gh :i* ! ,hudson "h passes4 ,! f\ndation & l[] /ory ( ! build+ are excavat$ out ( ! solid granite1 :i* appe>s at ! edge ( ! hill4 ,?is arrangem5t 0 int5d$ to keep ! l[] /ory cool1 & avoid1 9 ! case ( ! metal reflector1 sudd5 *anges ( temp]ature4 ,! ea/]n side ( ! l[] /ory1 h[ev]1 projects ov] ! br[ ( ! hill1 & is !re=e freely expos$ to ! air1 furni%+1 :5 desir$1 bo? access & ?or\gh v5tilation ?r\gh ! door4 ,! second /ory or sup]/ructure is ( wood1 l9$ inside ) bo>ds l ! /ory bel[4 ,!y s]ve to inclose 9 bo? cases a non-conduct+ %eet ( air4 ,! inside dim5sions ( bo? /ories tak5 toge!r are #ag-a_/b feet squ>e1 & #bb feet high1 to ! apex ( ! dome4 ,?is space is unnecess>ily l>ge = ! telescope1 :i* only requires a cyl9d] #ac feet 9 diamet] & #ac feet high4 ,a g5]al idea ( ! int]nal arrangem5t is ga9$ f ,fig4 #bh4 ,9 ,fig4 #ch1 a a is ! floor ( ! gall]y1 b b b ! circul> ap]ture 9 :i* ! telescope c c turns4 ,! /aircase is indicat$ by d4 ,! ,enl>g]1 #f1 re/s on ! %elf e1 ! helio/at be+ outside at f4 ,! door go+ into ! photographic room is at g1 h h are tables1 i ! wat] tank1 k ! tap & s9k1 l ! /ove1 m a helio/at %elf1 n ! door1 o ! w9d[4 ,illu/ration3 ,fig4 #ch4 ,plan ( ,obs]vatory 7upp] floor74 ,! build+ is kept v5tilat$ by op5+ ! door 9 ! l[] "p1 & ! dome %utt]1 se5 9 ,fig4 #cg1 = "s "t be=e us+ ! in/rum5t4 ,on a summ] day ! upp] p>ts1 & especially ^? close "u ! dome1 become )\t ?is precaution v hot1 & ?is occurr$ ev5 be=e ! t9 ro( 0 pa9t$4 ,bright t9plate seems n to be able to reflect by any means all ! heat t falls ^u x1 b w become s w>m 9 ,july t ros9 w melt on x1 & insects :i* h light$ 9 a few mom5ts dry up1 & soon become pulv]izable4 ,a k ( ^! facts l$ to ! ab&onm5t ( wood5 %ea?+ "u ! t91 = )\t x :5 night comes on ! accumulat$ heat radiates away rapidly1 & ceases to cause a]ial curr5ts ne> ! telescope4 ,! int]ior ( ! build+ is pa9t$ & wa9scot$1 & ! ro( is ornam5t$ p>tly 9 blue & oak1 & p>tly ) panels ( tulip-tree wood4 ,!re are only two w9d[s1 & !y are ne> ! s\!rn angles ( ! ro(4 ,:ile !y admit sun%9e on "s occasions1 !y c on o!rs be clos$1 & ! int]ior be r$uc$ to d>kness4 ,9 ! s\!a/ corn] a small op5+ e may all[ a sol> beam ?ree in*es 9 diamet] to come 9 f a helio/at outside4 ,! greate/ facilities are ?us pres5t$ = optical & photographical exp]im5ts1 = 9 ! latt] case ! :ole room c be us$ z a cam]a obscura4 b4 ,! ,dome4 ,! ro( ( ! obs]vatory is #bj feet squ>e4 ,! angles are fill$ 9 solid1 & a circul> space #ae feet 9 diamet] is left to be cov]$ by ! revolv+ dome4 ,al?\gh su* a con/ruction is ar*itecturally weak & liable to lose its level1 yet ! great advantages ( hav+ ! build+ bel[ squ>e1 & ! usefulness ( ! corn]s1 det]m9$ its adoption1 ! disadvantages be+ ov]come by a v light dome4 ,! dome is #af feet 9 outside diamet]1 & rises to a height ( #e feet above its base4 ,x is1 !re=e1 mu* flatt] ?an usual1 9 fact1 might h be5 absolutely flat1 ) ?is me?od ( m\nt+4 ,x w\ld !n h be5 liable1 h[ev]1 to be cru%$ 9 by ! deep w9t] sn[s4 ,x consi/s ( #cb ribs1 arcs ( a circle1 unit+ at a common c5tre above4 ,ea* "o is =m$ ( two pieces ( ?9 :itewood1 b1 ,fig4 #ci1 fa/5$ side by side1 ) ! be/ arrangem5ts ( ! gra9 = /r5g?4 ,!y are ?ree in*es wide & "o in* ?ick at ! l[] end1 & tap] gradually to #b-a_/b by #a4 ,illu/ration3 ,fig4 #ci4 ,jo9ts 9 ,t9 ( ,dome4 ,ov] ^! ribs t9plate is laid 9 triangul> /rips or gores1 ab\t #ah in*es wide at ! base1 & #aj feet long4 ,:]e ! adjac5t triangles ( t9 a a meet1 !y are n sold]$1 b are b5t toge!r4 ,?is all[s a c]ta9 am\nt ( contraction & expansion1 & is wat]-pro(4 ,x /r5g!ns ! ro( s mu*1 t if ! ribs bel[ 7 tak5 away1 ?is corrugat$ ?\gh ?9 dome w\ld probably su/a9 itself4 ,! t9 is fa/5$ to ! dome ribs b by extra pieces c ins]t$ 9 ! jo9t & d\bl$ ) ! o!r p>ts1 :ile bel[ !y are nail$ to ! ribs4 ,9 ! figure ! t9 is repres5t$ v mu* ?ick] ?an x is 9 reality4 ,?is dome1 al?\gh x has #bej squ>e feet ( surface1 only weighs #bej p\nds4 ,t at ! ,cambridge 7,massa*usetts7 ,obs]vatory1 #bi-a_/b feet 9 diamet]1 weighs #bh1jjj p\nds4 ,! slit or op5+ is mu* %ort] ?an usual1 only ext5d+ half way f ! base t[>ds ! summit4 ,x is 9 reality an incl9$ w9d[1 #b-a_/b feet wide at ! bottom1 #a-a_/b wide at ! top1 & #d feet long4 ,x is clos$ by a s+le %utt]1 z se5 9 ,fig4 #cg1 & ?is :5 op5$ is su/a9$ 9 position by an iron rod furni%$ ) a h+e at "o end & a hook at ! o!r4 ,! pr9cipal peculi>ity ( ! dome1 ! means by :i* x is rotat$1 rema9s to be describ$4 ,usually 9 su* /ructures roll]s or cannon balls are plac$ at int]vals "u ! edge1 & by means ( rack "w1 a motion ( revolution is sl[ly accompli%$4 ,"h1 on ! contr>y1 ! :ole dome b b b 7,fig4 #dj7 is support$ on an ar* h h h1 c>ry+ an axis a at its c5tre1 ar\nd :i* a slight direct =ce1 a pull ) a s+le f+]1 w cause movem5t1 & by a sudd5 pu% ev5 a qu>t] ( an entire revolution may be accompli%$4 ,x is desirable1 h[ev]1 to let x re/ on ! edge b b1 :5 n 9 use4 ,at c !re is an iron cat* on ! ar*1 by :i* ! lev] e1 t raises ! dome1 is held d[n4 ,! fulcrum is at d4 ,! lev] is h+$ ne> c1 s t :5 by be+ depress$ x %\ld h come 9 ! way ( ! telescope bel[1 ! l[] half g c be pu%$ up1 ! "p f c t[>d d /ill hold+ ! dome support$4 ,illu/ration3 ,fig4 #dj4 ,! ,dome ,ar*4 ,! ar* c be set across ! obs]vatory 9 any direction1 nor? & s\?1 ea/ & we/1 or at any int]m$iate position1 because ! abutm5ts :]e ! ends re/1 are =m$ by a r+ l l l1 fa/5$ r\nd ! circul> ap]ture1 ?r\gh ! /ation>y "p ( ! ro(4 ,:5 ! telescope is n 9 use1 & ! dome is let d[n1 s t !re is no long] an int]val ( a qu>t] ( an in* betwe5 x & ! re/ ( ! ro(1 x is conf9$ inside by f\r clamps & w$ges4 ,o!rwise1 ow+ to its lightness1 x w\ld be liable to be bl[n away4 ,^! clamps a1 ,fig4 #da1 are ?ree sides ( a squ>e1 made ( iron "o in* squ>e4 ,!y cat* above by a po9t 9 ! wood5 basis-circle ( ! dome b1 & bel[ are tight5$ by ! w$ge c4 ,illu/ration3 ,fig4 #da4 ,a ,dome ,clamp4 ,:5 ! dome is rais$ x is prev5t$ f mov+ lat]ally & slid+ (f by ?ree roll]s1 "o ( :i* is se5 at f1 ,fig4 #dj4 ,^! cat* aga9/ its inn] edge1 & only all[ slight play4 ,at fir/ x 0 ?\ght necess>y to h a subsidi>y half ar* at "r angles to ! o!r to hold x up1 b t is n[ remov$4 ,all ! p>ts "w v satisfactorily1 & ow+ to ! c>e tak5 to get ! ro(-circle & basis-circle flat & level1 no leakage takes place at ! jo9t1 & ev5 sn[ driv5 by high w9ds is unable to ent]4 c4 ,! ,obs]v]'s ,*air4 ,?is is n a *air 9 ! common acceptation ( ! ^w1 b is r a movable plat=m ?ree feet squ>e1 capable ( c>ry+ two or m p]sons r\nd ! obs]vatory1 & ma9ta9+ !m 9 an inv>iable position ) reg>d to ! telescope eyepiece4 ,illu/ration3 ,fig4 #db4 ,! ,obs]v]'s ,*air4 ,its g5]al arrangem5t is bett] compreh5d$ f ! sket*1 ,fig4 #db1 ?an f a labor$ description4 ,bel[1 x runs on a pair ( :eels a 7"o only is visible7 #i in*es 9 diamet]1 ^: axles po9t to ! c5tre ( ! circle ^u :i* !y run4 ,!y are prev5t$ f %ift+ outw>ds by a wood5 railroad b1 b1 & inw>ds by ! pal+ l1 l4 ,above1 ! *air moves on a pair ( small roll]s c1 :i* press aga9/ a circul> /rip or track d1 d1 nail$ ar\nd ! l[] edge ( ! dome op5+4 ,access to ! plat=m is ga9$ by ! /eps e1 e4 ,atta*$ to ! rail+ ( ?is plat=m1 & ne> x on ! telescope1 are two tables 7n %[n 9 ! figure7 = eyepieces1 ! slid+ platehold]1 c4 #e4 ,,! ,,photographic ,,laboratory4 ,?is section is divid$ into a1 ,description ( ! ,ap>tm5t2 & b1 ,photographic ,processes4 a4 ,description ( ! ,ap>tm5t4 ,! room 9 :i* ! photographical op]ations are c>ri$ on1 adjo9s & connects ) ! obs]vatory on ! s\!a/1 z is %[n 9 ,figs4 #bh & #ch4 ,x is #i by #aj feet inside1 & is suppli$ ) %elves & tables runn+ ne>ly all ! way r\nd1 :i* h ^u !m ! pr9cipal *emical reag5ts4 ,x is furni%$1 too1 ) an op5+ to admit1 f a helio/at outside1 a sol> beam ( any size1 up to ?ree in*es 9 diamet]4 ,! supply ( wat] is d]iv$ f ra9 fall+ on ! ro( ( ! build+1 & runn+ into a tank i1 ,fig4 #ch1 :i* w conta9 a ton weight4 ,! ro( exposes a surface ( #ecb squ>e feet1 & consequ5tly a fall ( ra9 equal to "o in* 9 dep?1 completely fills ! tank4 ,dur+ ! c\rse ( ! ye> ! fall at ?is place is ab\t #cb in*es1 s t !re is always an abundance4 ,9 ord] to keep ! wat] free f contam9ation1 ! ro( is pa9t$ ) a gr\nd m9]al comp\nd1 :i* h>d5s to a /ony consi/5ce1 & resi/s atmosph]ic influ5ces well4 ,! tank is l9$ ) lead1 b hav+ be5 9 use = _m ye>s = o!r purposes1 is ?or\ghly coat$ inside ) v>i\s salts ( lead1 sulphates1 c4 ,9 addition ! precaution is tak5 ( empty+ ! tank by a l>ge /opcock :5 a ra9/orm is approa*+1 s t any accumulation ( organic matt]1 :i* c r$uce nitrate ( silv]1 may be avoid$4 ,x has n be5 f\nd feasible to use ! well or spr+ wat] ( ! vic9ity4 ,! tank is plac$ close "u ! eaves ( ! build+1 s z to ga9 z mu* head ( wat] z is desirable4 ,f ne> its bottom a pipe t]m9at+ 9 a /opcock k1 ,fig4 #ch1 passes into ! ,laboratory4 ,9 ! nor!a/ corn] ( ! room1 & "u ! tap is a s9k = refuse wat] & solutions1 & ov] :i* ! negatives are develop$4 ,x is on an av]age ab\t twelve feet di/ant f ! telescope4 ,9 ano!r corn] ( ! room is a /ove1 resembl+ 9 con/ruction an op5 fireplace1 b suffici5t nev]!less to raise ! temp]ature to #hj ,f4 or high]1 if necess>y4 ,z a provision aga9/ heat 9 summ]1 ! walls & ro( are d\ble1 & a free space ) num]\s op5+s above is left = circulation ( air1 drawn f ! f\ndations4 ,! ro( is ( t9plate1 fa/5$ directly to ! raft]s1 )\t %ea?+1 9 ord] t heat may n accumulate to su* an ext5t dur+ ! day z to con/itute a s\rce ( di/urbance :5 look+ across x at night4 ,= conta9+ negatives1 :i* f be+ unv>ni%$ require p>ticul> c>e1 !re is at "o side ( ! room a case ) tw5ty %all[ draw]s ea* to hold eighte54 ,!y accumulate v rapidly1 & 7 x n = frequ5t reselections ! case w\ld soon be fill$4 ,on "s nights z _m z sev5te5 negatives h be5 tak51 mo/ ( :i* 7 wor?y ( pres]vation4 ,n less ?an #aejj 7 made 9 #ahfb & '#fc4 b4 ,photographic ,processes4 ,9 photographic manipulations ,i h _h ! advantage ( my fa!r's long cont9u$ exp]i5ce4 ,he work$ = _m ye>s ) bromide & *loride ( silv] 9 8 photo-*emical rese>*es 7,j\rnal ( ! ,frankl9 ,in/itute1 #ahcg71 & :5 ,dagu]re's beautiful process 0 publi%$1 0 ! fir/ to apply x to ! tak+ ( portraits 7,phil4 ,mag41 ,june1 #ahdj7 9 #ahci2 ! mo/ important ( all ! applications ( ! art4 ,subsequ5tly he made photographs ( ! int]f]5ce spectrum1 & asc]ta9$ ! exi/5ce ( great gr\ps ( l9es ,m1 ,n1 ,o1 ,p1 above ,h1 & totally invisible to ! nak$ eye 7,phil4 ,mag41 ,may1 #ahdc74 ,! importance ( ^! results1 & ( ! /udy ( ! /ructure ( flames conta9+ v>i\s elem5t>y bodies1 t he made at ! same "t1 are only n[ excit+ ! int]e/ !y des]ve4 ,9 #ahej1 :5 8 "w on ,physiology 0 9 prep>ation1 & ! num]\s illu/rations _h to be produc$1 ,i le>nt microscopic photography1 & soon aft] prep>$ ! mat]ials = ! collodion process1 !n rec5tly inv5t$ by ,scott ,ar*]4 ,we produc$ 9 #ahef _m photographs "u a p[] ( #gjj diamet]s1 by ! means describ$ 9 ! next section4 ,at fir/ ! usual processes = portrait photography 7 appli$ to tak+ ! ,moon4 ,b x 0 soon f\nd necess>y to ab&on ^! & adopt o!rs4 ,:5 a collodion negative has to be enl>g$--& ?is is always ! case 9 lun> photography1 :]e ! orig9al picture is tak5 at ! focus ( an object glass or mirror--imp]fections invisible to ! nak$ eye assume an importance :i* causes ! rejection ( _m o!rwise excell5t pictures4 ,"s ( ^! imp]fections are p9holes1 co>s5ess ( granulation 9 ! r$uc$ silv]1 liability to /a9s & m>k+s1 spots produc$ by du/4 ,^! 7 all avoid$ by wa%+ (f ! free nitrate ( silv] f ! s5sitive plate1 be=e expos+ x to ! light1 & aga9 submitt+ x to ! action ( wat]1 & dipp+ x back into ! nitrate ( silv] ba? be=e develop+4 ,! quantity ( nitrate ( silv] necess>y to developm5t :5 pyrogallic acid is us$1 is h[ev] bett] procur$ by mix+ a small quantity ( a /&>d solution ( t salt ) ! acid4 ,! op]ation ( tak+ a lun> negative is z foll[s4 ,! glass plates #b-c_/d #c-a_/d in*es are kept 9 nitric acid & wat] until want$4 ,!y are !n wa%$ "u a tap1 be+ well rubb$ ) ! f+]s1 :i* h ( c\rse be5 prop]ly clean$4 ,!y are wip$ ) a t[el kept = ! purpose4 ,next a few drops ( iodiz$ collodion are p\r$ on ea* side1 & spread ) a piece ( cotton flannel4 ,!y are !n poli%$ ) a l>ge piece ( ?is flannel1 & deposit$ 9 a close dry plate box4 ,?is sy/em ( clean+ ) collodion 0 sugge/$ by ,major ,russel1 to ^: skilful exp]im5ts photography is indebt$ = ! tann9 process4 ,x c]ta9ly is mo/ effective1 ! dry+ pyroxyl9e remov+ e injuri\s impurity4 ,!re is nev] any tr\ble f dirty plates4 ,! /ock ( plates = ! night's "w1 a doz5 or s1 be+ ?us prep>$1 "o ( !m is tak51 & by movem5t ?r\gh ! air is fre$ f fibres ( cotton4 ,x is !n coat$ ) filt]$ collodion be+ held ne> ! damp s9k4 ,! coat$ plate1 :5 suffici5tly dry1 is imm]s$ 9 a #dj gra9 nitrate ( silv] ba?1 acidifi$ ) nitric acid until x r$d5s litmus pap]4 ,! exact am\nt ( acid 9 ! ba? makes 9 ?is 8,wa%$ ,plate ,process0 b little diff]5ce4 ,:5 ! iodide & bromide ( silv] are ?or\ghly =m$ ! plate is remov$1 dra9$ = a mom5t1 & !n held "u ! tap till all greas9ess1 z x is call$1 disappe>s4 ,bo? front & back receive ! curr5t 9 turn4 ,x is !n expos$1 be+ c>ri$ on a little wood5 /&1 ,fig4 #dc1 cov]$ ) filt]+ pap] to ! telescope1 & deposit$ on ! slid+ platehold] :i* has be5 set to ! direction & rate ( ! moon1 :ile ! plate 0 9 ! ba?4 ,! "t ( exposure is asc]ta9$ by c\nt+ ! beats ( a half-second p5dulum4 ,! me?od by :i* exposure )\t caus+ tremor is accompli%$1 is z foll[s3 ,a yell[ glass slides ?r\gh ! eyepiece-hold]1 ,fig4 #cc1 j 9 front ( ! s5sitive plate1 & is put 9 be=e ! plate4 ,! yell[-color$ moon is c5tr$ on ! collodion film1 & ! clepsydra & slide are set 9 motion1 ! mass ( ! telescope be+ at re/4 ,a pa/ebo>d scre5 is put 9 front ( ! telescope1 & ! yell[ glass tak5 out4 ,aft] #bj seconds ! in/rum5t rema9+ /ill unt\*$ & motionless1 ! scre5 is )drawn1 & z _m seconds all[$ to elapse z desirable4 ,! scre5 is !n replac$ & ! plate tak5 back to ! photographic room4 ,illu/ration3 ,fig4 #dc4 ,plate ,c>ri]4 ,aft] be+ aga9 put "u ! tap to remove any du/ or impurity1 x is dipp$ into ! nitrate ba? = a few seconds4 ,two dra*ms ( a solution ( protosulphate ( iron #bj gra9s1 acetic acid #a dra*m1 & wat] #a ounce1 is p\r$ on x4 ,z soon z ! image is fairly visible ?is is wa%$ (f1 & ! developm5t cont9u$ if necess>y ) a weak solution ( pyrogallic acid & citro-nitrate ( silv]--pyrogallic & citric acids ea* #a_/e gra91 nitrate ( silv] #a_/aj gra91 wat] #a dra*m4 ,9 ord] to measure ^! small quantities /&>d solutions ( ! sub/ances are made1 s t two drops ( ea* conta9 ! desir$ am\nt4 ,!y are kept 9 bottles1 ?r\gh ! corks ( :i* pipettes desc5d to j bel[ ! level ( ! liquid4 ,?is avoids all necessity ( filt]+1 & yet no blemi%es are produc$ by p>ticles ( float+ matt]4 ,illu/ration3 ,fig4 #dd4 ,pipette ,bottle4 ,dur+ ! e>li] "p ( ! developm5t1 :5 ! protosulphate ( iron is on ! film1 an accurate judgm5t c be =m$ z to ! prop] l5g? ( "t = ! exposure 9 ! telescope4 ,if ! image appe>s 9 #aj seconds1 x w acquire an appropriate d5sity = enl>gem5t 9 #de seconds1 & w h ! m9imum ( :at is call$ fogg+ & ! smalle/ granulations4 ,if x takes long] to make its fir/ appe>ance ! exposure mu/ be l5g!n$1 & vice v]sa4 ,illu/ration3 ,fig4 #de4 ,develop+ ,/&4 ,! latt] "p ( ! developm5t1 :5 re-developm5t is practis$1 is purposely made sl[1 s t ! gradation ( tones may be v>i$ by *ang+ ! proportion ( ! +r$i5ts4 ,z x w\ld be tiresome & uncleanly to hold ! plates 9 ! h&1 a simple /& is us$ to keep !m level4 ,x consi/s ( a piece ( ?9 wood a1 ,fig4 #de1 ) an ord9>y wood screw1 z at b1 go+ ?r\gh ea* corn]4 ,f\r wood5 pegs1 z at c1 furni% a support = ! plate d4 ,by ! aid ( ?is contrivance & ! wa%+ sy/em1 ,i seldom get my f+]s m>k$1 & :at is mu* m important1 r>ely /a9 a picture4 ,:5 ! degree ( int5sity mo/ suitable = subsequ5t enl>gem5t is rea*$1 t is1 :5 ! picture is l an ov]done positive1 ! plate is aga9 flood$ ) wat]1 treat$ ) cyanide ( potassium or hyposulphite ( soda1 once m wa%$ & set ^u an angle on filt]+ pap] to dry4 ,x is next morn+ labell$1 & put away unv>ni%$ 9 ! case4 ,to ! rem>k t ?is process implies a great deal ( extra tr\ble1 x c only be repli$ t m negatives c be tak5 on ea* night ?an c be kept1 & t1 ev5 7 x n s1 "o good picture is wor? m ?an any numb] ( bad ones4 ,al?\gh ! above is ! me?od at pres5t adopt$1 & by :i* excell5t results h be5 obta9$1 x may at any mom5t give place to "s o!r1 & is inde$ be+ cont9ually modifi$4 ,! defects x pres5ts are two--fir/1 ! "t ( exposure is too long1 & second1 !re is a c]ta9 am\nt ( lat]al diffusion 9 ! ?ickness ( ! film1 & 9 consequ5ce a degree ( %>pness inf]ior to t ( ! image produc$ by ! p>abolic mirror4 ,! %orte/ "t 9 :i* ! moon has be5 tak5 9 ?is obs]vatory has be5 "o-?ird ( a second1 on ! tw5ty-fir/ day1 b on t occasion ! sky 0 s+ul>ly cle>1 & ! intr9sic spl5dor ( ! light great4 ,! full moon "u ! same circum/ances w\ld h requir$ a mu* %ort] exposure4 ,a p]son1 h[ev]1 :o has put 8 eye at ! focus ( su* a silv]$ mirror w n be surpris$ at ! %ortness ( ! "t ne$$ = impress+ ! bromo-iodide film2 ! brilliancy is s great t x impairs vision1 & = a long "t ! expos$ eye fails to di/+ui% any mod]ately illum9at$ object4 ,! light f #ahh squ>e in*es ( an almo/ total reflect+ surface is cond5s$ ^u #b squ>e in*es ( s5sitive plate4 ,occasionally a condition ( ! sky1 ! rev]se ( t m5tion$ above1 occurs4 ,! moon assumes a pale yell[ color1 & w cont9ue to be ( t non-act9ic t9t = a mon? or six weeks4 ,?is ph5om5on is n conf9$ to special localities1 b may ext5d ov] great tracts ( c\ntry4 ,9 ,augu/1 #ahfb1 :5 our regim5t 0 encamp$ 9 ,virg9ia1 at ,h>p]'s ,f]ry1 ! atmosph]e 0 9 ?is condition !re1 & 0 also simil>ly affect$ at ! obs]vatory1 m ?an #bjj miles di/ant4 ,z to ! cause1 x 0 n =e/ or prairie fires1 = none ( !m ( suffici5t magnitude & duration occurr$1 b 0 probably du/ 9 a /ate ( m9ute division4 ,no cont9u$ ra9 fell = sev]al weeks1 & ! clay ( ! ,virg9ia roads 0 turn$ into a f9e p[d] = a dep? ( _m in*es4 ,! ,upp] ,potomac riv] 0 s l[ t x c\ld be cross$ dry-%od4 ,on a subsequ5t occasion :5 ! same /ate ( ?+s occurr$ aga91 ,i expos$ a s]ies ( plates 7^: s5sitiv5ess 0 n less ?an usual1 z 0 prov$ by a /&>d artificial flame7 to ! image ( ! full moon 9 ! #ae-a_/b in* reflector = #bj seconds1 & yet obta9$ only a mod]ately int5se picture4 ,?is 0 #dj times z long z common4 ,^u all photographic pictures ( cele/ial objects ! influ5ce ( ! atmosph]e is se51 be+ sometimes great] & sometimes less4 ,to obta9 ! be/ impressions1 j z /eady a night is necess>y z = critical obs]vations4 ,if ! image ( ,jupit] is all[$ to pass across a s5sitive plate1 a /reak almo/ z wide z ! planet is left4 ,x is easily se5 n to be cont9u\s1 z x w\ld h be5 7 !re no atmosph]ic di/urbances1 b compos$ ( a set ( p>tially isolat$ images4 ,besides ?is planet1 ,i h also tak5 impressions ( ,v5us1 ,m>s1 d\ble />s1 c4 ,an attempt has be5 made to ov]come lat]al diffusion 9 ! ?ickness ( ! film by ! use ( dry collodion plates1 m p>ticul>ly ^? ( ,major ,russel & ,dr4 ,hill ,norris4 ,^! pres5t1 x is true1 a f9e & v ?9 film dur+ exposure1 b :ile develop+ are s *ang$ by wett+ 9 _! me*anical condition t no advantage has result$4 ,x 0 :ile try+ !m1 t ,i asc]ta9$ ! great control t hot wat] ex]cises ov] ! rapidity ( developm5t1 & "t ( exposure1 ow+ p>tly no d\bt to increase ( p]meability 9 ! collodion film1 b also p>tly to ! fact t *emical decompositions g on m rapidly at high] temp]atures4 ,i h attempt$ 9 va9 to develop a tann9 plate :5 x & ! solutions us$ 7 at #cb ,f41 & ?is ?\gh x _h _h a hundr$ times ! exposure to light t 0 dem&$ :5 ! plate 0 kept at #adj ,f4 by w>m wat]4 ,proto*loride ( palladium1 :i* ,i introduc$ 9 #ahei1 is frequ5tly employ$ :5 x is desir$ to increase ! int5sity ( a negative )\t alt]+ its ?ickness4 ,?is sub/ance w augm5t ! opacity #af times1 )\t any t5d5cy to injure ! image or produce m>k+s4 ,x is only at pres5t kept out ( g5]al use by ! sc>city ( ! metal4 #f4 ,,! ,,photographic ,,enl>g]4 ,two di/9ct arrangem5ts are us$ = enl>g+1 a1 = ,l[ ,p[]s v>y+ f #a to #be2 & b1 = ,high ,p[]s f #ej to #gjj diamet]s4 a4 ,l[ ,p[]s4 ,! ess5tial feature 9 ?is contrivance is an entire novelty 9 photographic enl>gem5t1 & x is s sup]ior to sol> cam]as1 z !y are call$1 t !y are nev] us$ 9 ! obs]vatory n[4 ,x consi/s 9 employ+ in/ead ( an a*romatic comb9ation ( l5ses1 a mirror ( appropriate curvature to magnify ! orig9al negatives or objects4 ,! advantages are easily enum]at$1 p]fect co9cid5ce ( visual & *emical foci1 flat field1 absolute %>pness ( def9ition4 ,if ! negative is a f9e "o1 ! enl>g$ pro(s w be z good z possible4 ,illu/ration3 ,fig4 #df4 ,! ,photographic ,enl>g]4 ,! mirror is ( #i in*es ap]ture1 & #aa-a_/b in*es focal l5g?4 ,x 0 poli%$ on my ma*9e to an elliptical figure ( #h feet di/ance betwe5 ! conjugate foci1 & 0 int5d$ to magnify #g times4 ,at fir/ ! :ole mirror 0 all[$ to (ficiate1 ! object be+ illum9at$ by diffus$ daylight4 ,b x 0 soon app>5t1 t al?\gh a m9ute object plac$ 9 "o focus 0 p]fectly reproduc$ at ! o!r1 sev5 times z l>ge1 yet a l>ge "o 0 n equally well def9$ 9 all its p>ts4 ,i det]m9$ !n to produce ! enl>g$ image by pass+ a sol>-beam #a-a_/b in* 9 diamet] ?r\gh ! orig9al lun> negative--plac$ 9 ! focus ne>e/ to ! mirror--& all[+ x to fall on a portion ( ! concave mirror1 #a-a_/b in* 9 diamet]1 at "o side ( ! v]tex4 ,be+ reflect$1 x returns pa/ ! negative1 & goes to =m ! magnifi$ image at ! o!r focus ( ! ellipse4 ,9 ,fig4 #df1 a is ! helio/at on a /one %elf outside2 b a silv]$ glass mirror1 to direct ! p>allel rays ?r\gh c1 ! negative2 d is ! elliptical mirror2 e an ap]ture to be p>tly clos$ by diaphragms2 f a rackwork movem5t c>ri$ by ! tripod g2 ! curta9 h h %uts out /ray light f ! int]ior ( ! obs]vatory4 ,! ap]ture i is also diaphragm$1 b is %[n op5 to indicate ! position ( ! helio/at1 ! %elf ( :i* jo9s ! outside ( ! build+ at l4 ,! dott$ l9e po9ts out ! c\rse ( ! light1 :i* com+ f ! sun falls on ! helio/at mirror a1 !n on b1 ?r\gh c to d1 & !nce return+ ?r\gh e to ! s5sitive plate 9 ! plate hold] k4 ,! di/ance ( ?is la/ c be made to v>y1 be+ ei!r two feet or tw5ty-eight feet f d4 ,9 ! latt] case a magnify+ p[] ( ab\t #be results1 ! moon be+ made ?ree feet 9 diamet]4 ,! s5sitive plate is c>ri$ by a frame1 :i* screws to ! side wall ( ! build+1 & c be easily *ang$ 9 position4 ,! focuss+ is accompli%$ by ! rack f4 ,:]e s small a "p 7#a-a_/b in*7 ( ! surface ( ! mirror is us$1 a rigid adh]5ce !n to ! true foci ( ?is ellipse is n dem&$1 ! mirror seem+ to p]=m equally well :e!r magnify+ #g or #be times4 ,!oretically x w\ld seem to be limit$ to ! =m] p[]4 ,if in/ead ( plac+ a lun> photograph1 :i* 9 ! nature ( ! case is nev] absolutely %>p1 at c1 "s natural object1 z = in/ance a section ( bone1 is atta*$ to ! frame mov$ by f1 !n "u a p[] ( #be times x is z well def9$ z 9 any microscope1 :ile at ! same "t ! am\nt ( its surface se5 at once is mu* l>g] ?an 9 su* in/rum5ts1 & ! field is flat4 ,if ! int5tion 71 h[ev]1 to make microscopic photographs1 a mirror ( mu* %ort] focal l5g? w\ld be desirable1 "o approa*+ m to ^? ( ,amici's microscopes4 ,by ! aid ( a concave mirror us$ ?us obliquely1 or exc5trically1 all ! difficulties 9 ! way ( enl>g+ disappe>1 & pictures ( ! greate/ size c be produc$ 9 p]fection4 ,i %\ld long ago h made lun> photographs ( m ?an #c feet 9 diamet]1 except = ! difficulties ( manipulat+ su* l>ge surfaces4 ,9 ord] to secure a con/ant beam ( sunlight a helio/at is plac$ outside ! obs]vatory1 at its s\!a/ corn] f1 ,fig4 #ch4 ,?is beam1 :i* c be s5t = an entire day 9 ! direction ( ! e>?'s axis1 is int]cept$ z %[n at b1 ,fig4 #df1 & ?us if ne$$ an exposure ( _m h\rs c\ld be giv54 ,! int]ior ( ! obs]vatory & photographic room be+ only illum9at$ by fa9t yell[ rays1 no cam]a box is requir$ to cut (f /ray light4 ,! eye is by ^! means kept 9 a mo/ s5sitive condition1 & ! focuss+ c be effect$ ) ! critical accuracy t ! optical arrangem5t all[s1 no correction = *romatic ab]ration be+ dem&$4 ,i h made all ! p>ts ( ?is app>atus s t !y c be easily sep>at$ or *ang$4 ,! flat mirrors are ( silv]$ glass1 & are us$ ) ! silv]$ side t[>d ! light1 to avoid ! d\ble image produc$ :5 reflection f bo? sides ( a p>allel plate ( glass is p]mitt$4 ,! l>ge concave mirror happ5s to be ( speculum metal1 b x c be repoli%$ if necess>y by means ( a f\r in* poli%]1 pass$ 9 succession ov] e *ord ( ! face4 ,a yell[ film ( t>ni% easily accumulates on metal specula if !y are n c>efully kept1 & decreases _! photographic p[] s]i\sly4 ,( ! mak+ ( ,rev]ses4--,9 addition to ! use ( ! ,enl>g] = magnify+1 x is f\nd to h important advantages 9 copy+ by contact4 ,! picture ( ! image ( ! moon produc$ 9 ! telescope is negative1 t is1 ! lights & %ades are rev]s$4 ,9 enl>g+ su* a negative rev]sal aga9 takes place1 & a positive results4 ,?is positive _c1 h[ev]1 be us$ to make pr9ts on pap]1 because 9 t op]ation rev]s+ ( light & %ade once m occurs4 ,x is necess>y !n at "s /age to introduce /ill ano!r rev]sal4 ,?is may be accompli%$ ei!r by pr9t+ f ! orig9al negative a positive1 :i* may be enl>g$1 or else pr9t+ f ! enl>g$ positive a negative to make ! pap] pro(s f4 ,9 ei!r case a collodion film1 prop]ly s5sitiz$1 is plac$ beh9d ! positive or negative1 & ! two expos$ to light4 ,if diffus$ light or lamplight is us$1 ! two plates mu/ be z closely 9 contact z possible1 or ! %>pness ( ! result+ pro( is greatly less ?an ! orig9al4 ,?is is because ! light f9ds its way ?r\gh 9 _m v>i\s directions4 ,if ! two plates1 h[ev]1 are plac$ 9 ! cone ( sunlight com+ f ! ,enl>g]1 & at a di/ance ( fifte5 or tw5ty feet f x1 ! light passes 9 /raight l9es & only 9 "o direction ?r\gh ! front picture to ! s5sitive plate beh9d4 ,i h n be5 able to see "u ^! circum/ances any p]ceptible dim9ution 9 %>pness1 ?\gh ! plates _h be5 #a_/af ( an in* ap>t4 ,x is p]fectly feasible to use wet collodion in/ead ( dry plates1 no risk ( scrat*+ by contact is incurr$1 & ! :ole op]ation is easily & quickly p]=m$4 ,! "t ( exposure1 #e seconds1 is ( conv5i5t l5g?1 b may be increas$ by putt+ a less reflect+ surface or an unsilv]$ glass mirror 9 ! helio/at4 ,a diaphragm ) an ap]ture ( half an in* if plac$ at e1 ,fig4 #df1 to %ut out ne$less light1 & avoid injur+ ! %>pness ( ! rev]se by diffusion ?r\gh ! room4 ,9 enl>g+ o!r diaphragms are also = ! same reason put 9 ! place ( ?is "o4 ,= a half moon = in/ance1 a yell[ pap] ) a half circul> ap]ture1 ^: size may be f\nd by trial 9 a few m9utes1 is p9n$ aga9/ e4 ,! enl>g$ pictures obta9$ by ?is app>atus are mu* bett] ?an c be obta9$ by any o!r me?od kn[n at pres5t4 ,! effect1 = in/ance1 ( a portrait1 made life-size1 is v /rik+4 ,"s a/ronom]s h suppos$ t advantages w\ld arise f tak+ orig9al lun> negatives ( l>g] size 9 ! telescope1 t is1 f enl>g+ ! image two or ?ree times by a suitable eyepiece or concave a*romatic1 be=e x rea*$ ! s5sitive plate4 ,b ap>t f ! fact t a reflector w\ld !n h all ! disadvantages ( an a*romatic1 ! atmosph]ic difficulties1 :i* 9 reality con/itute ! great ob/acle to success1 w\ld n be dim9i%$ by su* means4 ,! app>5t advantage1 t ( n magnify+ defects 9 ! collodion1 is n ( mu* mom5t1 = :5 developm5t ( ! photographs is prop]ly conduct$1 & ?or\gh cleanl9ess practis$1 imp]fections are n produc$1 & ! size ( ! silv] granules is n objectionable4 b4 ,high ,p[]s4 ,al?\gh negatives ( a/ronomical objects h n z yet be5 made :i* c\ld /& ! high p[]s ( ! arrangem5t ab\t to be describ$1 yet !y be> ! l[] p[]s well1 & give promise ( improvem5t 9 ! future4 ,photography ( microscopic objects z usually describ$1 consi/s 9 pass+ a beam ( light ?r\gh ! transp>5t object into ! comp\nd body ( ! microscope1 & receiv+ x on its exit f ! eyepiece ^u a gr\nd glass or s5sitive plate4 ,! difficulty :i* besets ! in/rum5t g5]ally1 & int]f]es ) ! production ( f9e results1 arises f ! unc]ta9ty ( asc]ta9+ ! focus or place = ! s5sitive plate4 ,= if ! collodion film be put :]e ! image on gr\nd glass seems be/ def9$1 ! result+ photograph w n be %>p1 because ! act9ic rays d n =m _! image !re1 b ei!r f>!r f or ne>] to ! l5ses1 dep5d+ on ! am\nt ( ! *romatic correction giv5 by ! optician4 ,practically by repeat$ trials & v>iation ( ! place ( ! s5sitive comp\nd1 an approximation to ! focus ( ! rays ( maximum photographic int5sity is rea*$4 ,illu/ration3 ,fig4 #dg4 ,microscope = ,photography4 ,dur+ my fa!r's exp]im5ts on light1 & m p>ticul>ly :5 engag$ 9 ! inv5tion ( portrait photography1 he f\nd t ! ammonio-sulphate ( copp]1 a deep blue liquid1 w sep>ate ! m refrangible rays ( light1 ! rays conc]n$ 9 photography1 f ! re/4 ,if a beam ( sunlight be pass$ ?r\gh su* a solution1 inclos$ betwe5 p>allel plates ( glass1 & !n cond5s$ ^u an object on ! /age ( a microscope1 a blue color$ image w be =m$ on ! gr\nd glass1 above ! eyepiece4 ,if ! place ( be/ def9ition be c>efully asc]ta9$1 & a s5sitive plate put 9 ! /ead ( ! gr\nd glass1 a %>p photograph w always result4 ,besides1 !re is no dang] ( burn+ up ! object1 z !re w\ld be if ! unabsorb$ sunlight 7 cond5s$ on x1 & h5ce a mu* l>g] beam ( light & mu* high] p[]s c be us$4 ,! be/ results are atta9$ :5 an image ( ! sun produc$ by a %ort focuss$ l5s is made to fall ^u & co9cide ) ! transp>5t object4 ,9 #ahef we obta9$ photographs ( frog's blood disks1 navicula angulata1 & sev]al o!r simil> objects "u a p[] ( #gjj diamet]s1 excell5tly def9$4 ,s9ce !n sev]al hundr$s ( microscopic pictures h be5 tak54 ,9 ! figure1 a is ! helio/at1 b a l5s ( ?ree in*es ap]ture1 c ! glass cell = ! ammonio-sulphate ( copp]1 d ! object on ! /age ( ! microscope e1 f ! cam]a = ! gr\nd glass or s5sitive plate4 ,above ! figure ! c\rse ( ! rays is %[n by dott$ l9es4 99 99 99 99 99 ,9 conclud+ ?is acc\nt ( a ,silv]$ ,glass ,telescope ,i may answ] an inquiry :i* d\btless w be made by _m ( my read]s1 :e!r ?is k9d ( reflector c ev] rival 9 size & effici5cy su* great metallic specula z ^? ( ,sir ,william ,h]s*el1 ! ,e>l ( ,rosse1 & ,mr4 ,lassell8 ,my exp]i5ce 9 ! matt]1 /r5g!n$ by ! rec5t successful attempt ( ,m4 ,f\cault to figure su* a surface m ?an ?irty in*es 9 diamet]1 assures me t n only c ! f\r & six feet telescopes ( ^? a/ronom]s be equall$1 b ev5 excell$4 ,x is m]ely an affair ( exp5se & pati5ce4 ,i hope t ! m9ute details ,i h giv5 9 ?is pap] may lead "s "o to make ! ef=t4 ,,ha/+s1 ,,we/*e/] ,,c\nty1 ,,new ,,york1 #ahfc4 ,po/script4--,s9ce writ+ ! above ,i h complet$ a photograph ( ! moon #ej in*es 9 diamet]4 ,! orig9al negative f :i* x has be5 made1 be>s ?is magnify+ well1 & ! picture has a v impos+ effect4 ,,publi%$ ,,by ,,! ,,smi?sonian ,,in/itution1 ,,wa%+ton ,,city1 ,,july1 #ahfd4