| OCR Text |
Show . _,.' i '- , . . "' .' H"'* . , 1 .‘ _ v . . an.» .' . -,, , - ,~ ‘ . .A. - .. .- ,. , ,; .4 .~ .._ A. ,_ \_ , : "-‘y‘ ,1i, h. I; .. . . ,7 . n- , . fee . DIAN. TO FIND A TRUE MERI /" ' A MANUAL OF LAND SURVEYING. 108' s t, the common engineer' firs , rk wo s thi for ed ne We piece of tical are or circle. A transit fitted with ver not be useful though it is l wil ss gla rk da or e shad imperative. place within a minute or e th of de itu lat e Th . Second taken from a map. two. This can readily be raction containing less ref an me of le tab A Third. . res. than half a hundred figu This declination of the sun. Fourth. A table of the nt h._ Hence only tude and slowly in‘azimut own ect azimuth which is sh an error in altitude will aff e th acazimuth compared with in ge an ch ll sma e th by izon-, nge. Now bring the hor companying altitude cha ing sure that tal plates to zero and, be o for the colthe vertical circle reads zer (or note its in. limation line horizontal E nting at the' m n dex errors) and take a poi o a: u can be gained .a sun. A better centering '1 l cross wire E by bringing the horizonta "'4 h gives a ar the upper limb whic ne y ver , r figure. is a vest-p makers. A good form C. A ller, of Washington, D. out by George N. Saegmu show how triangle involved will glance at the spherical , ed to determine azimuth. us be y ma n su e th ily eas =2 s the In the figure, P represent P time of place of the sun at the cal tri- eri observation. In the sph it‘is angle SPZ we know PZ, for ce. the co-latitude of the pla Nbfilzbfl' Al a. {1) °~ ' bisected. '_small segment to be ‘33 i" a" f per limb of th zontal wire to the up and sight the se the alidade plate vertical circle and loo e horizontal circle. ZS which is the complement of AS, sun at latter is the altitude of the nsit. as measured by the tra the time of observation from d of the sun and is foun PS is the co-declination lina- by subtracting the dec the table of. declinations lina- . ed to the sign of the dec des =co-1atitude, and z = coin which p =co-altitude; azi z. This angle'gives the clination and S=p+s+ reckoned instant of observation muth of the sun at the angle The supplement of the nt. poi th nor the om fr _ nt, referred to the south poi would show its-azimuth muth. the usual origin of azi Shown by the gained horizontal slow motion er low e th th wi ng vi Ha e horimotion quickly move th center, with the vertical e sun. Readlthe ~ m " tion from 90°, paying he angle e three sides of the tri tion. We then have th the by compute the angle at Z known and can readily formula sin ( 1} S-p') sin ( a: 8-5) sin 1lZ: sin p sin 5 \ 109 t except near noon, time of the day will do raction for uncertainties in ref favorable time except s, since or sunset. This appear would be near sunrise the aziand from it compute de itu alt e th e ur as me we y in altisun is changing rapidl muth at' the time the that part of instrume tis by many of our table is furnished gra ocketpamphlet sent zenith éx ._ e n or eight o'clock in th Field Work.-- About seve nsi afternoon set the tra t morning or at five in the a some prominent mark, as over a point commanding y An ola to some building. church spire, flag pole or cup but the most BY THE DIAN on OTHER LINE To FIND A TRUE MERI SUN. Z the celestial pole of the earth, the d of the observer, an S .. . ‘ . and read th selected terrestial mark rmina- pend upon a single dete Should we care not to de four times, y be repeated say ma ion rat ope s thi tion ce as aconly a mean value twi thus furnishing us not reement of ation but by the ag erv obs gle sin a as curate lves we can judge . se em th g on am s ult res the individual the seciability. By taking rel l era gen ir the of much rument in ations with the inst ond and fourth observ mitfull vertical circle per he -t on ti si po ed ers the rev from both the error resulting ly tru ting this-we eliminate nt not being of the instrume the horizontal axis vertical circle. index error of the and the horizontal and the made Aug. 24, 1895, Sample observationsn, are given on the followmg io method of computat . page. . v,‘ |
