SEXTANT Optical Law
SEXTANT ERRORS A Adjustable errors
5. Vernir error (adjustable by marker) B Non adjustable errors
1. Centering error / / / / / / / / / / Index bar \qHkcsuf pivot onf graduation arc \ center wGif r&SdaomaMumifh
jzpfonfh error jzpfonf/ ¤if; error &Sdr&Sdod&ef index bar udk arc ay:wGif a&SUaemufa&TUMunfhygu index bar
ESifh graduation arc Mum;tuGmta0;onf wpfae&mESifhwpfae&m rwlygu ¤if; error &Sdrnf/ Error rsm;vQif od
omí error enf;vQif laboratory wGifom &SmEdkifonf/
2. Graduation error / / / / / / / / / / Sextant wGif graudate vkyfxm;aom degree trSwftom;rsm; rrSefuefrIaMumifh
jzpfaom error jzpfonf/ ¤if; error udkodEdkif&ef object ESpfckMum;axmifhudk sextant jzifhwdkif;jyD;? &aomwefzdk;ESifh theodolite jzifh wdkif;í&aom wefzdk;ESifh EdIif;,SOfjcif;jzifhodEdkifonf/ odkYr[kwf altitude wlaom Mu,fESpfvHk;Mum;
axmifhudkwdkif;jyD; ¤if; Mu,fESpfvHk;Mum;wGif&Sdrnfh axmifhwefzdk;udk wGufMunfhjcif;jzifhvnf; check vkyfEdkifonf/
3. Micrometer error / // // // // / Micrometer wpfywfvSnfhvQif graduation arc ay:wGif index mark onf 1 degree a&TUvmrnf/ xdkodkYra&TUvQif error &Sdrnf/
4. Shade error / // // // // / Shape glass rsm;onf plane of the sextant ay:wGif axmifhrSefrusvQifaomfvnf;
aumif;? rsufESmjyiftcsif;csif; rjydKifvQifaomfvnf;aumif; shape error jzpfrnf/ Optical error [kvnf; ac:Edkif
onf/ &Sdr&Sd check vkyf&ef object ESpfckMum;axmifhudk shape glass xnfhí wdkif;jyD;? shape glass rygbJwdkif;aom reading ESifh EdIif;,SOfMunfhygu odEdkifonf/ Negligible error jzpfonf/
5. Prismatic error / / / / / / / / / / Index mirror, horizon glass ESifh shape glass rsm;\ a&SUESifhaemuf rsufESmjyif
rsm;onf wpfckESifhwpfck rjydKifaomaMumifh tvif;wef;rsm;,dkifjyD; jzpfay:vmaom error jzpfonf/ ¤if; error udk check vkyf&ef object ESpfckMum;&Sdaxmifhudkwdkif;yg/ xdkYaemuf index mirror udkjzKwfjyD;? wpfbufodkYvSnfhí jyefwyfyg/
xdkYaemuf object ESpfckMum;&Sdaxmifhudk jyefwdkif;yg/ axmifhwefzdk;ESpfckuGmjcm;ygu error &Sdonf/
6. Worm and Rack error / / / / / / / / / / Micrometer wGifyg&Sdaom tangent screw \ 0uftl&pf (worm) ESifh sextant lower limb wGif&Sdaom gear (rack) rsm; wdkufpm;oGm;aomaMumifh jzpfay:aom error.
Sextant Parallax
The angle subtended at an object by an index glass and the horizon glass of a sextant. I.E ESifh side error r&Sdaom sextant jzifhta0;wGif&Sdaom object wckudk sextant zero set vkyfí telescope
xJwGif reflected ESifh true image onfwxyfxJ&Sdrnf/ object rS index mirror udk½dkufaom ray onf object rS horizon glass udk½dkuf ray 2 ckMum; object wGifjzpfay:aomaxmifhonf tvGefao;i,fNyD;r&Sdoavmufjzpfonf/
xdkYaMumifh ¤if; ray 2 ckwpfxyfwnf;usonf[k ,lqEdkifonf/
odkYaomf dist; eD;aom object wckudk zero set vkyfNyD;MunfhvQif wpfxyfwnf;rusawmhay/ tb,faMumifh
qdkaomf ray 2 ckMum; object wGif jzpfay:aomaxmifhonf odompGmjzpfay:vmaomaMumifhjzpfonf/ Object onf
eD;vmonfESifhtrQ object wGifjzpfay:aomaxmifhonf ydkNyD;BuD;vmrnf/ ¤if;axmifhwefzdk;udk sextant parallax [k
ac:onf/
¤if; Parallax wefzdk;udkodvdkvQif reflected object ESifh true object udkxyfatmif micrometer udka&TUNyD; reading udkzwfvQif&onf/
2 miles xufeD;aom object rsm;wGif sextant parallax &Sdonf/
* Sextant \ \ \ \ \ arc onf onf onf onf onf 1/6 or a circle 60•om&SdNyD;tb,fhaMumifh om&SdNyD;tb,fhaMumifh om&SdNyD;tb,fhaMumifh om&SdNyD;tb,fhaMumifh om&SdNyD;tb,fhaMumifh arc wGifwGifwGifwGifwGif120•yg0ifoenf;/yg0ifoenf;/yg0ifoenf;/yg0ifoenf;/yg0ifoenf;/
- Sextant principle aMumifhjzpfygonf/
- Sextant onf object 2 ckMum;&Sdaxmifhudkwdkif;aom instrument jzpfonf/
- Sextnat jzifh object 2 ckMum;axmifhudkwdkif;aom observer taejzifh ¤if;axmifhwefzdk;udk arc ay:wGif
Object wckudk index glass jzifhzrf;,lNyD; horizon glass rSjrif&aom true object ESifhwpfxyfwnf;usatmif
a&TU&onf/
- xdkodkYawGYvQifrSef2 ckMum;wGif Angle jzpfay:onf/
- ¤if;wefzdk;rSm Arc ay:wGif index bar awGU&onfh arc yrmPESifhnDrQonf/ - Sextnat \ arc onftrSefwu,f 60•om&Sdonf/
- Index bar udk arc ay:wGif 60•xdawGUvQifrSef2 ckMum;axmifhonf 60•&Sdrnf/
- odkYaomf Sextant principle t& object ESpfck Mum;axmifhwefzdk;onf rSefESpfckMum;&Sd axmifwefzdk; \
2 q &Sdonf/
xdkYaMumifh Graduation rsm;udk mark vkyf&mwGi frSefESpfckMum;wGifajymif;vJoGm;rnfh axmifhwefzdk; 60•udktjyif
wGifajymif;vJoGm;rnfh axmifhwefzdk; 120° jzpfatmif pdyfxm;jcif;jzpfonf/ Sextant wGif mark vkyfxm;aom 1°
onf ¤if; arc \ 1/2 degree om&Sdonf/ Graduation wefzdk;rsm;onf arc \wu,fhwefzdk;udk az:jyxm;jcif; (udk,f
pm;jyKjcif;)r[kwfyJ angle rsm;udk udk,fpm;jyKxm;jcif;jzpfayonf/
Back-lash of a micrometer sextant
- Sextant \ index bar (index mark) udk zero setting vkyfNyD; minute tenf;i,fa&TUyg/ - Star wpfvHk;udkMunfhyg/ reflected star ESifh true star txufatmufuGJaernf/
- Reflected ESifh true star wdkYudkwxyfwnf;jzpfatmif micrometer udkvSnfhNyD;xyfyg/ (bring up vkyfonf
[kac:onf/)
- xdkuJYodkY Reflected ESifh true wpfxyfwnf;jzpfonfhtcsdefwGif H.Z glass ESifh index mirror parallel jzpf
onf/ xdktcsdefwGif main arc ESifh micro meter f index mark rsm;onf zero udkjyae&rnf/
- Zero rSuGmaeoavmufyrmPonf I.E jzpfNyD; “on the arc” udk (-) tjzpfowfrSwfí off the arc udk (+) tjzpfowfrSwfyg/ I.E yrmPudkrSwfxm;yg/ xdkYaemuf micro meter udk anteclock wise vSnfhyg/ - txufygtwdkif; star 2 ckvHk;udkxyfatmif “brining up” jyefvkyfyg/
- xdkYaemufI.E yrmPudkzwfyg/
* ¤if; I.E yrmP2 ckwlnD&rnf/ rnDvQif ¤if; I.E 2 ckjcm;em;í &aomyrmPonf back-lash jzpf
onf/ (¤if;udk total back-lash [kac:onf/)
* ¤if; back-lash yrmPrsm;vQif correction vkyfay;&rnf/enf;2 enf;jzifhvkyfEdkifonf/
(a) Clock-wise direction ESifh bringing up vkyfí&aom I.E ESifh anti- clock wise direction ESifh bringing up vkkyfí
&aom I.E 2 ckaygif;\ mean I.E udk sextant observation wGif apply vkyfyg/ (back-lash azsmufNyD;om;jzpfrnf/) (b) Sextant altitude wGif clock-wise (odkY) anti-clock wise direction ESifhbringing up vkyfí&aom I.E udk apply
vkyfyg/ &&Sdvmaom observed altitude wGif total back-lash udk apply vkyfyg/
* Bringing up udk “on the arc” wGifvkyfxm;aom I.E jzifh apply vkyfygu back-lash udk observed altitude wGifEIwfyg/
* Bringing up udk“off the arc” wGifvkyfxm;ygu back-lash udkaygif;yg/ * New instrument wGif back-lash onf negligible jzpfonf/
* Vessel udk astern qGJpOf propeller rS,ufxkwfvdkufaom a&rsm;udkvnf; back-lash water [kkac:onf/
Sextant Certificate wGif - (rdwf? quf? a&? vD? yg? yg? 'dwf? qdkif;)wGif - (rdwf? quf? a&? vD? yg? yg? 'dwf? qdkif;)wGif - (rdwf? quf? a&? vD? yg? yg? 'dwf? qdkif;)wGif - (rdwf? quf? a&? vD? yg? yg? 'dwf? qdkif;)wGif - (rdwf? quf? a&? vD? yg? yg? 'dwf? qdkif;)
1. Maker's name, 5. The magnification power of the telescopes,
2. Sextant Serial Number, 6. The permanent errors at various angles,
3. Radius of the Sextant, 7. Date of Manufacture,
BAROMETER
Atmospheric presure udkwdkif;aom instrument jzpfonf/ Pressure unit udkoHk;onf/
Pressure = Fore per Unit Area
S.I. system wGif pressure unit rSm BAR jzpfonf/
1 bar = 10 tonnes weight per square meter (10 ts. / M2 )
odkYr[kwf
1 Kg weight per square centimeter (1 Kg / cm2 ) 1 mb = 1 bar / 1000
Imperial system wGif pressure unit rSm inch of mercury jzpfonf/
1 inch of mercury = 14.7 lb. / in.2
urÇmajrrsufESmjyifteD; (ground level) wGif avxk\ average pressure onf 1 bar xuf slightly
rsm;onf/ Standard Barometric Pressure (S.B.P) onf S.I unit wGif 986.9 mb jzpfonf/ (987 mb) Imperial unit wGif 14.5 lb. / in2 jzpfonf/ S.B.P. &&SdEdkif&ef vdktyfaom standard rsm;rSm -
Latitude 45º N/S jzpfjyD; height onf mean sea level jzpfonf/ Temperature rSm standard temperature
jzpf&rnf/ ¤if; standard oHk;ckESifh udkufnDaomtajctaewGif &&Sdaom barometer reading onf S.B.P jzpfonf/ Nautical publication rsm;ESifh weather charts rsm;ay:wGifazmfjyxm;aom pressure rsm;rSm S.B.P rsm;jzpfonf/
Barometer ESpfrsdK;&Sdonf- (1) Mecurial barometer
wpfbufyGifhzef>yef (Marine tube) about 1 M (36 inches.) xJwGif R.D. 13.6 &Sdaom mercury
udkjznfhjyD; tube udk ,m,Dydwfí cistern (cGuf) xJodkYarSmufcsvQif zef>yefxJrS mercury rsm; cistern xJodkY avQmusvm
rnf/ odkYaomf 25 cm cefYomavsmhusoGm;jyD; tube xJwGif 75 cm cefYusefaernf/ Mercury rsm;ukefatmif
rxGufoGm; jcif;rSm cistern xJodkY a&mufoGm;aom mercury rsm;\ surface udk tjyifrSavxku
zdxm;aomaMumifhjzpfonf/xdkavsmhusoGm;aom av[me,fudk "Torricelli vacuum" (after torricelli) [kac:onf/ Torricelli av[me,fxJodkY avvHk;av;rsm; (air bubble) rsm;0ifoGm;vQif barometer reading wGif error rsm;jzpfvmEdkifojzifh marine tube xJwGif air trap udkwyfqifí umuG,fxm;onf/
Mecurial barometer wGifatmufyg error wdkYjzpfay:Edkifygonf-
(1) Pumping error : vessel onf seaway wGif vIyf&Sm;aeaomaMumifhvnf;aumif;? gusty winds
aMumifhvnf;aumif; tube xJrS mercury level onfvIyf&Sm;jyD; wdusaom reading udkr&&SdEdkifyg/
¤if; error udkumuG,fEdkif&ef marine tube xJwGif air trap \txufydkif;ü capillarity tube udk
wyfqifxm;onf/
(2) Capillarity error : capillarity tube udk xnfhxm;aomaMumifh mercury \ surface wGif "meniscus" (Mercury level cHk;jcif;) jzpfay:aponf/ xdkuJhodkYjzpfjcif;rSm mercury \ surface
wGif tension jzpfaejyD; tube ESifh mercury wdkYtMum;jzpfay:aom friction aMumifhjzpfonf/ ¤if; error udk compensate vkyf&ef mercury \ top level ESifh tube udkxdaeaom level ESpfcktMum; mean udkzwf&rnf/
(3) Capacity error : mecurial barometer wGifxnfhxm;aom mercury yrmPonf constant
jzpfonf/ Marine tube xJrS height of mercury udkwdkif;&ef cistren xJrS mercury level udk
tajccHxm;onf/ odkYaomf avxk pressure ajymif;vJaomtcg cistern xJrS mercury rsm;onf tube xJodkY xdk;0ifoGm;jyD; level edrfhusoGm;onf/ xdkYaMumifh height of mercury udkwdkif;&mwGif standard level ajymif;vJoGm;ojzifh reading wGif error jzpfaponf/ xdkuJhodkY rjzpfap&ef enf;ESpfck
jzifh compensate vkyfxm;onf/
- Kew pattern cistern xJrS edrfhusoGm;rnfh mercury level twdkif; graduation udk avQmhcs
jyD; mark vkyfonf/ xdkYaMumifh inch barometer rsm;wGif pressure rsm;vmonfESifhtrQ
jrifhwufoGm; rnfh tydkif;rS graduation rsm;onf actual 1 inch xuf 1/25 inch avQmhí marking vkyfxm; onf/
- Fortin pattern cistern xJwGif mercury level jr§ifh^ESdrfhí&atmif pDpOfxm;jyD; standard level xufajymif;vJoGm;onfESifh level adjust vkyfí reading zwfEdkifatmif pDpOfxm;onf/ (4) Observational error :
- Marine tube xJrS torricelli vacuum udk mercury rsm;u balance vkyfxm;jcif;jzpfonf/
- Barometer reading vkyfonfhtcg observer \ eye level onf Marine tube wGif&Sdaom
ta&SUESifhtaemuf vernir mark rsm;ESifh wpfwef;wnf;jzpfaeap&rnf/ rjzpfvQif reading error jzpfEdkifonf/
- Mercury level rzwfrD attached thermometer udkt&ifzwf&rnf/ Observer \ body heat
aMumifh reading wGif error jzpfEdkifonf/
(5) Height : nautical publication rsm;ESifh chart rsm; map rsm;wGif azmfjyxm;aom barometer pressure rsm;onf S.B.P rsm;jzpfonf/ xdkYaMumifh vuf&Sdae&mwGif zwfí&aom barometer reading udk sea level wGif&Sdrnfh reading tjzpf ajymif;ay;&rnf/ Barometer onf mean sea level xuf approximately 10 M (30 ft.) jrifhoGm;wdkif; + 1 mb vkyfí? edrfhoGm;wdkif; -1 mb
vkyfay;&rnf/ Gold slight jzifhvnf; correction vkyfEdkifonf/
(6) Latitude : urÇmBuD;\ surface onf polar regions rsm;wGif center ESifheD;jyD; equator wGif center ESifh a0;onf/ xdkYaMumifh mercury wGifoufa&mufaom gravitational force onf equator
rSmxuf pole wGif ydkrdkcHpm;&onf/ xdkYaMumifh latitude 45º N/S udk standard latitude
tjzpfowfrSwfí vuf&Sda&mufaeaom latitude ESifh latitude 45º uGmjcm;rnfh yrmPtwGuf correction vkyfay;&rnf/ ¤if; correction udk her mesjecty's stationery office (HMSO) table
rsm;wGif &Sm,lEkdifonf/ odkYr[kwf gold slight jzifh correction vkyfEdkifonf/
(7) Temperature : tube xJrS mercury onf thermometer xJu mercury uJhodkY ylvQifyGí
at;vQif usHKUonf/ xdkYaMumifh temperature rwlaomae&mrsm;rS barometer rsm;onf wlrnfr[kwf
acs/ xdkYaMumifh Correct reading &&SdEdkifrnfh standard temperature wpfckudk owfrSwf&onf/ Standard temperature = latitude 45º wGif mean sea level ü barometer udk correct reading
jzpfaprnfh temperature jzpfonf/ Milibar jzifhazmfjyaom barometer trsm;pk\ standard temperature onf 285ºK (12º C) jzpfjyD;? inch of mercury jzifhazmfjyaom barometer rsm;wGif standard temperature onf 28.6º F jzpfonf/
- Latitude 45º wGif&Sdrnfh standard temperature udk vuf&Sd position latitude wGif &Sdrnfh temperature tjzpf correction udk apply vkyfvdkufvQif fiducial temperature [kac:onf/
- Fiducial temperature udk vuf&Sd position height wGif&Sdrnfh temperature tjzpf correction apply vkyfvQif adjusted fiducial temperature [kac:onf/
- Adjusted fiducial temperature ESifh vuf&Sd vessel a&mufaeaom ywf0ef;usif temperature (actual temperature) udkjcm;em;vQif correction vkyf&rnfh temperature &rnf/ ¤if; correction
vkyf&rnfh temperature yrmP 6º K &Sdwdkif; ± 1 mb correction vkyfay;&rnf/ (actural temperature uenf;vQif +, rsm;vQif - )
Oyrm Lat. 60º N, barometer with standard temperature 285º K (12º C) reads 1014.2 mb, height of barometer 60 ft. above sea level, attached thermometer reads 288º K (15º C), find S.B.P. Standard temperature of barometer (12° C) = 285.0º K
For Lat. correction (15º ) = 7.5º K (from HMSO table)
Fiducial temperature = 292.5º K
Height correction (for 60 ft.) = 12.0º K (1º for 5 ft.)
Adjusted fiducial temperature = 304.5º K Actual temp. (from attached thermometer) = 288.0º K
Temperature for correction = 16.5º K
Require correction = 16.5º / 6º = 2.75 mb (1 mb for each 6º K difference)
Barometer reading = 1014.2 mb
Corrections = 2.75 mb
Correct sea level reading = 1016.95 mb
Gold Slide Operation
vuf&Sda&mufaeaom position lat. eJY high above mean sea level udk wpfwef;wnf;jzpfatmifxm;yg/ Attached thermometer \ top level ESifh wnfhwnfhrS apply vkyf&rnfh correction wefzdk;udk zwf,lyg/ ¤if; correction barometer reading wGif apply vkyfyg/
PRECISION ANERIOD BAROMETER