thk new-york exhibition illustrated.

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tronomy have not even yet furnished lunar tables of all the esna e accuracy.Yet of all astronomical methods, that of moon culminations, when checked hycorresponding and nearly simultaneous observations on the moon s posi ion, mat 6at standard observatories, is, on the whole to be preferred. This check effectual ybanishes errors of lunar theory from the results by making the time .accumulate very brief. Such check observations are made for the cons sui yseveral American observatories, and copies of the Greenwich o servo, '

also promptly furnished by Mr. Airy for its use. Mr. Walkei gave a "S*of perfection to the method and details of reducing moon culminations.. ®

provements of lunar theory by Longstreth’s corrections, Pi of. leicestions, and various contributions from other sources, as embodied m ie aeican Nautical Almanac, give hopeful promise that the time is at ian ,

accuracy with which the lunar tables will predict the moon s place, may rorre _

to exceed that of any single observation; a result which will masponding observations at standard observatories unnecessary. ,.

But foremost and best of all, where the existence oftelegiap ° .

wires makes it available, is the method of comparing local times y 1 ^

telegraph. An astronomical clock is arranged to make an automatic re ...seconds on a fillet, cylinder, or disc of paper. The observer recor 8 .

of observation by touching a key which governs the opening or c osmg 1

arranged to interpolate an instantaneous record of the touch on 16 ,

sheet which receives the record of seconds, or clock-beats. Whet ler touchbe in the circuit, a thousand miles from the recording appaiatus, or v ,

of it, whether he telegraph transits or clock-boats, or whethei the c oc <its own beats, the result is that the local act of opening or c oslI1 S ^ ’

makes its instantaneous record at the recording station, which recorinterpolated among the clock seconds records, can be read wit grea ^

and gives the local time of the key touch exactly, save the smal oorre j° o . t ] ietime of current transmission, and that for armature time. The , V6 °. flnsm ittin"galvani? current has been found from many experiments, ma e ^ ^ „ 000 miles

signals successively in opposite directions, to be between 15,000 anc i , ngtan _in a second, and to depend somewhat on the conducting me liim. .

taneous interchange of signals to any extent, brings into the closes posMtion the two local times or the longitudes. Telegraphic longituc e i e ^

be determined with an accuracy very nearly identical with t la w i ‘given to the local time determinations. The transit instrument use ^ instru .local times, gives to this element a high degree of accuracy. n ® ° Those

ments, belonging to the Coast Survey, is exhibited at theCiysta aused in this work, are from twenty-six to forty-eight inches in oca eare constructed by Simmes of London, and Wurdeman of Washington.

On the whole, telegraphic longitude differences need scarce y a s i ,

best latitude results in reliable accuracy. Thus for the first time as l para ppossible to compare the astronomical and geodetic measurements o arc .

lels in such a manner as to give valuable results. The coast survey wi. e0( j ea yembrace some excellent arcs of parallels, from the discussion ownmay expect some important data, bearing on the earth’s figure.

To connect American and European longitudes with the utmos possracy, most elaborate observations have been made by all the preva en ’

for the purpose of obtaining the exact difference between Greenwich andbridge Observatory times. Great numbers of chronometers have een ^

across the ocean, a single expedition, under the immediate c irec ioBond, carrying one hundred and seventy-five. The aceomp is ie ir , . g

Liverpool Observatory, Mr. Hartnup, united in the observations neces ^

expedition, the results of which are undergoing computation, un er ithe Superintendent, by Prof. George P. Bond. The mean result for the me no ychronometers—that by moon culminations, and that by occu ta ions,eclipses,—strange to say, agree less perfectly with each other, iansets of observations by each method do. The adopted longitu e oObservatory from Greenwich, based on the observations up to *> i29.5s. To this point, all Coast Survey longitudes are at present refene d o thata close connection is established between all well deteimine pom

An incidental reference to azimuth observations, may not be a ’conducting a trigonometrical survey, the lines between stations m . ^

not only by latitudes and longitudes, but the horizontal angles which^hey makewith the meridian, or their bearing from the North, must be meastned atoet ^stations by observations, on circumpolar stars. These o seiva twenty-

the Coast Survey at the primary latitude *^5 the triangulation,

four inch theodolites, used for measuring the honzonta fe

Two methods are ik use, each of which is available both by nighami.by <lay.

fn the first, circumpolar stars are observed tomgthe ^ western elonga-and the forty-five minutes following their gieatest . ,

.tions, the motion in azimuth being then very slow and reducib y Pmula. Polaris is principally, and Delta and Lambda Ursa toons, and 5

Cephei are occasionally, used. Sets of aboo ‘^wthe 0«Mrtmade at each elongation. In the second method, wh P

Survey, corresponding observations, at equal times before and after the star cul-minates, are made in sets, which require for their reduction nothing but the tak-ing of their mean. These culmination observations, of course, depend on an accu-rate knowledge of the local time or meridian, an element always necessary forother purposes at each astronomical station. A meridian determined from thefast-moving equatorial stars, by a forty-six inch transit, is exceedingly accurate forslow-moving Polaris. Errors from this source are really trifling in comparisonwith those which occur in referring the star to the horizon. These observationson culminations are read on different portions of the theodolite limb, and are thusfree from that approach to identical readings, which exists in elongation records.This method, though new, is now much used, and is found to give results quiteequal to that by elongations. The stars observed, and the arrangement of sets ofobservations, are the same in both. Where the theodolite is small, the starimage in an artificial horizon is observed upon as a substitute for the stridinglevel. In observing azimuths, a lamp by night and a mark by day, are placed on thesame vertical about a mile off, and the star positions are referred to them in thefirst instance. The angle between tho lamp or mark and the station is then meas-ured, either on the theodolite limb, or by the micrometer of the telescope. Ob-servations for both of these angles require to be so multiplied on successive daysand nights, as to eliminate tho effects of irregular lateral refraction. Thus atOausten’s 120, at Mt. Pleasant 70, and on Jehossee Island 329 observations weremade. When possible, fore and back azimuths, or those at each extremity of tholine should be observed,—this furnishing a criterion of accuracy and of stationerrors. On discovering the general prevalence of station errors on the Const Sur-vey, Prof. Baclie proceeded to multiply azimuth stations very much, and the fruitof this is found in the fact, that these azimuths give not merely an independent,confirmation of station errors in a general way, but even afford a close numericalverification of their precise amounts: a result truly surprising and we beliovequite without precedent. So much has thus been achieved in making out thofacts relating to local deviations, as manifested in these station errors, that wogrow impatient to learn from the pendulum, if tho intensity of gravity also un-dergoes variations corresponding to those of its direction.

In reviewing what has now been said of latitudes and longitudes, and of themeans and methods employed in determining them, we see much occasion forcongratulation, in the rapid progress hitherto made in giving perfection to theways and means for these fundamental elements of geodesy, in the liberal spiritwhich actuates alike republican and imperial governments to contribute to thepractical development of the earth’s geometry, and finally in the honorable posi-tion which not even prejudice can deny to our young nation, already the contrib-utor to science of American methods for both latitude and longitude determina-tions, marked by superior simplicity, practical facility, and accuracy of results.

LITHOGRAPHY.

A LOYS SENEFELDER, the inventor of lithography, the indicator of nearlyall its applications, and a man of true genius, was born at Prague, in 1771.Ilis father belonged to the court theatrical troupe of Munich, and was anxiousthat his son should become a lawyer, and sent him to the University of Ingolstadtwith that view; but a strong dramatic inclination on the part of Aloys fortu-nately led him to abandon legal studies, and to undertake, with true enthusiasm,the composition of dramas. To this occupation he joined the role of an actor fora time, but after a brief experience of the disgusts incident to this vocation, hedevoted himself in Munich to literary labor, passing through the usual ordeal otdiscouragements which so constantly awaits an unknown author. A publishercontracted to make a specified payment for his works if the printing was finishedat a stipulated time; but though the poor author himself worked vigorously, bothat the case and at the press, tho printing was not done in time, and he lost hiswork both of head and hand. Smarting under this infliction, he conceived theidea of dispensing with the inoro costly aids of printing, and becoming a froe andindependent author, by doing every thing himself except the buying and reading,for which he mainly expected the public to volunteer.

It is interesting to watch the progress of this brave mind, isolated by poverty,reduced to a defiant chartism in respect to mechanical ways and means, tryingone expedient after another, but never conceiving of despair in this strugglefor independence. He first invented stereotyping in sealing wax, whichproved too brittle a material for the purpose. He then had recourse to themethod of writing in reverse on a copper-plate etching ground of varnish, andthen eating the letters into the plate with acid. But this would not do, for hisplate wore away too fast. He then tried tin plates, hut the acid action wasfound inadequate. His free recourse to erasing in these trials, consumedpumice stone to such an extent, that tho poor hero’s pocket grow gaunt underthe expense even of this cheap material. Then it was, that his memory recurred,to the white stones he had seen on the banks of the Iser, the true lithographic

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