Weekly national intelligencer. [volume] (Washington [D.C.]) 1841-1869, 1853-11-26


only the determinations OF relative positions.
But the computing departments has other and higher
duties On it deyoyes the combination Of all the results
by the various observers Of the survey and the emna
ton of the great facts Of the earths figure by the
nected discussion OF Of merdans and Of parallels
The geodesy Of the survey must its definite shape
and mature all its grand results in the computing depart
ment, and through these labors must be the world
wide laurels for the work as whole The formul@ foi
computations and discussions, although shaped hand
in similar early geodetc works ought to be cons
dered as past Improvement and much has already been
done (though enough still remains to invite effort
in simplifying and expanding the grasp of these funda
mental instruments. In organizing the system of com
putatons for the Coa Survey, the geodetic formula
were examined and carried to closer degree of ap
Proclamation, tested by reference to the maxma of the
functions involved and put into forms convenient
for computing The formula for computing azmuths has
also been much smplfed Uniformity of computations
Tor the entire work has been secured by the use Of print
ed forms.
There is great variety of delicate and difficult sub
ects connected with the probable of methods and
sets of observations the character of catalogues and
particular Instruments the general physical elements
observinglike refracton, personal equation &c-be-
side some abstract Investigations in pure and APP
piled analysis; all Of which demand for their successful
treatment clear heads skilfp mastery Of mathematical
TOOLS and quick perception Of the relations between alb
stract and physical elements Thus it will be that
the computing department needs combination Of
skill and sagacty, with the ordinary attribute of
practical efficiency in the routine of work of computation
and in the systematic arrangements and preservation
results In all these respects we believe it is part-
oularly fortunate.
The computations incident to the study of tidal pheno-
mena for local tide tables and for general discussions
performed either under the Superintendent eye
by the efce tidal computers these being not exactly
part of the Computing Department but acting under
separate direction.
Next in order is the Drang Department. In this the
Typographical and photographic sheets which usually
made scales of 1100 00h and l-20000th of nature
are reduced to the scales proper for publication and their
details prepared for engraving The opographer by
the plane table and its auxaries, determines the var-
accidents of the ground in their positions and
relations, and delneates them in Clear strong but
finished style proper for his large scale He represents
hills by contour lines level curves twenty feet apart
vertically while fields, marshes, houses forests &c.
indicated by appropriate conventional deineatons The
office draughsman takes the several plane table sheets
covering the ground of the final map, indicated by
map project and reduces all these to the publication
SCALE thus making what is called reduction. The first
step in making reduction is accurately to plot the
fresh sheet all the triangulaton and well determined
plane table points within its limits, which points afford
constant check and means of correctly COM
bining the various original sheets.
Three modes of reducing constantly employed in
this office. The most elegant and rapid though hardly
the most accurate, is that by means of the idd
IN which, by regulating the projection squares of the
original exactly to coincide in apparent position
with corresponding squares the reduction all their
contents traced by the pencil in their reduced CORE
lative forms and positions This is probably the best
method of reducing soundngs and it affords excellent
means of yerifcaton The is limited in its power
of changing scales by the ratio Of about to FOUR
beyond this it loses dstinctness and makes
intermediate reduction. 1t is also found to be very
trying to the eyes, that the draughtsman must often
take respite The of the lens correct the camera
for paraax is due to Mr. BORDEN, the Director Of the
Massachusetts survey
The method by corresponding squares is the one most
used especially for outlines and is rather preferred for
the finest reductions In this process either frames with
squares made of fine thread applied to the original
n rula tlv iy;p al
on an attached sheet of tracing paper fish glue Cor
squares then either ruled the reduc
ton Sheet represented by reducing frame of the
proper scale Then the lines and points transferred
by the eye from each original square its reduced cor
relative Much practice is requisite for the and
rapid use either of the camera method of that by
squares but experience gives the draughsman great ia
cility and high accuracy in using either
The pentegraph is the third mode Of reducing in USE
depends almost entirely for its utility and
the workmanship and combination of the particular
made in the Coast Survey Office several years since
but the results unsatisfactory to the
method TO be thrown aside Recently, however, it has
been revived by using much perfect instrument
made by Mr.. WIN. WURDEAAN, of Washington and IL
may now be said to be trial. with a fair prospect of
better This requires good draughsmen FORTS
use-one to move the tracing point and watch the
reducing pencil. 1t is a great desderatum to OBJ
tain pencipoint which will retain its sharpness for
some time and yet make clear linea problem yet
quite solved by FABER.
The contour lines either reduced In pencil and
made the guide for the hdcureaq the hills
by short perpendicular pen-sroke the are re-
duced in ink and the engraver puts in the hachures
course only practicable, however, with a few first class
engrayers The best reductions have almost microsco
pic accuracy Of detail while in point finish and style
they rarely much inferior and sometimes superior
the engraving They executed great part under
a magnityng glass In reducing the photography only
limited selection of the soundipgs actually made is
tanned, the choice being made view to presenting
important characteristics
Curves of depth carefully made out and these serve
guides for the engravers in sanding the bottom slopes
The drawing department has much work do in prepar
ing sketches for the annual reports and in
calls for information by traced copies.
Next order the EngrapiRg Department. In this
the finished reductions and sketches of the drawing de-
transferred by engrayers onto or into copper
plates all the lettering Of sailing directions, Names
script and the views Of headands and harbor entrances
are engraved or etched from the originals.
The processes Of the copperplate engravers few
and simple, though the attainment Of skill in their use
requires long practice The engraycr first the
outlines and details Of his work on sheet Of
fsh-glue Having flashed delicate film Of wax over the
surface Of his he reyerses his tracing its
correct position the flm and so transfers the
black lines Of his tracing the plate The lines being
thus printed the wax he follows them with tracing
point and lightly them into copper SO as to afford
sufficient guidance for the detailed strokes Of the graver
Most Of the Office engraving is executed with the graver
and the dry point but the process Of etching is employed
for Of the views and too for reconnos
topography In this process the engaver lays his
ground Of wax and then with ueede-point draws the
desired lines through the coating. When he has
completed this drawing he cncoses his engraved in
dyke, and pours an acid solution which is
suffered for carefully regulated interval into the
copper along the lines Of drawing the surface being else
where protected by the coating The lettering is all
done with the graver in pure English letters and
Coast Survey letter specimens perhaps superior in
nth ate urnvinfr