' v * 1 *0on V.

% ar > Jle dismisses an engineer in it, to make the neces-on .®" e ®ents for constructing a chart, and to give as'” ea of the level of the country as possible. Fearing,

“Oty (

«»ti 0n Hi at, should the balloon be suffered to change its® a <l fru 8 * Vei l \ ie earth, the enemy might anticipate his design( ''frer eil t r: J te 'b he permits the engineer to raise himself toj,j a 'Htudes in the atmosphere, if necessary, but not to"’'th atl . Perpendicular station. The engineer is providedHso furn' 1 !!' Ument ^ or ^ le measul ' eme nt of angles, which isetl 8ine er l. ! et ^ with a plumb-line : it is asked, how can the11 Sol u( Ulm the object of his general ?

Sar He v (;t ,- i °”-T The engineer must take two stations in the^ring lca ' Hne, whose difference he may ascertain by mea-j® die oth C ° r< ^ ^ et out > to ra >se the balloon from one station^ >ne a „ er ' one of these, the lowest, for example, letdirg^ 1 ® Hie angles made by the zenith with the visualMedline ^ towan ' s the points whose position he wishes toS ,-ct 0l)e ° n Hie chart ; then, among these points, let him'Hi d en ’ .''eh he will consider as the first, and which we

!, B Sles £!° mi

tl <3 ‘® s for — nate A ’ ^ et H'™ a l so measure successively thest ' dir e j ne( ' Hre visual ray directed to the point A, andtf 11 ' 011 ) leu • towai ’Hs all the other points. In the secondf! <: Hsual * llri raea sure the angles formed by the zenith withHie Sp ra T s directed to all the points of the country : andi '^hen ° >Serva Hons, he may construct the chart required.^Htli ar e acquainted with the angles formed by the

%! rds H>e tle '

on

^Ola,

tiro,;, '"’o

two visual rays directed from the two stationssame point, we know that such point is at oncet a Mliu ' ba. ( eterill >iiate and known conic surfaces, withtl^ of tiu S ’ *' av ' n g their axes in the same zenith, the dis

^ Cor »m

} ^' r ecte|j e j! c 1 ua ' r| ted with the angle formed by the visualHorn the first station to this point, and by that

6 tw ° sta. 6 ' 1 ' a P' ces equal to the difference of the altitudes ofth 6 „„ 1Qns ’ an( f the angles formed by their generators

non axis equal to the angles observed. Also,

i* '>eot„j e acc l ua inted with the1 'ect nJ tea

'lie'll kase USt ( IKew ' se be on a third conic surface, with a cir-

> ' w uose inclined axis is the visual ray directed fromRation - - J

„ -''-u ar<Js Hie point A, we know that the point con-

"Wb^stlike •

l ! ® r 8'

‘‘ tst st at r“ uon Awards the point a, having its apex in thepotato,! 0 ”’ an(i forming an angle between its axis andf 6 M, tl,. <r l>ial to the angle observed. The point consi-vei«, re f or e, will be found at the same time on conic sur-th l'^tlv* • Cn 0,, lar bases, of known form and position ; con-«, .ycon U ttlUst l >e the point of their common intersection ;t|, lr >t(;r s „ truct 'ng the horizontal and vertical projections otl c ' la n Ct !° n ’. We shall obtain the position of the point onVi,,. ^Viti;' v 'ni its elevation above or below others.

Hl, n hia v ? Ut Va rying from these considerations, the construc-f>y .7 rendered more simple, by some of the methods

,i ?t 4 *tt 2 ^ bed: for wUh a knnw,pd<rA nf n,i ’ T Ja

- for with ‘a knowledge ^of^the^angles

ki w nt a' 16 first stat ' on b y H‘f visu , al , ia J„ vds a il the otherJ*** \ a i an ^ by the rays directed to * ^ 0 f these

v ‘t V 'Hti?o" OV, ' in o Hie angles i ' ornied ^ hem t0 the horizon,it,*' V zenith, it is easy to reduce them ge i eC t-

bip' ruc Hng their horizontal projec i • represent

00 chart, an arbitrary point,to rep

Hie zenith of the balloon, of

%^\ Hne through it, to represent th<ip throug h

directed towards A ; drawing • t5on 0 f

ri ^ ht Hues, making with ^ projec _ ^ . gkS 1 tl,i les e qual to those reduced to the l or -, zcm talof these lines must contain ^the 1 ^ ^■^iti' 1 ', 8 ’ ther lts cor respondent point of co y. country'VJ z to fmd the distance of this P 0,n t ; ca l pro-N?' P or this purpose, take, m the, ^on the projection of the zenith of dm d ^

Hieh in p ar t s of the scale are distan3 Y

other equal to the measured distance of the two stations, andthrough these points draw right lines making with the zenithangles equal to those observed for an identical point ofcountry ; which lines will cross each other in a point whosedistance from the zenith will be the distance required ; andby measuring it on the corresponding ray, beginning from theprojection of the balloon, we shall have on the chart, theposition of the point of country. The same two right lines,in the vertical projection, will, by their intersection, determinethe height of such point ; therefore, by taking on the verticalprojection, the heights of all the points of country above acommon horizontal plane, we shall be able to determine thequotas suitable for all the points of the chart, and likewisethe level of the country.

“ This construction is so easy, that it does not require afigure.

“ The right line drawn from the projection of the zenithof the balloon to that of the first point, a, observed, havingbeen in the first instance traced upon the chart arbitrarily,it follows that the chart is not adjusted to the cardinal points,and, indeed, in the observations laid down, we find nothingby which to determine the objects observed towards them.But if an engineer observe on the earth, the angle made bythe meridian with a visual ray directed from the foot of thezenith towards one of the points placed on the chart, and ifhe describe this angle upon its projection, he will have thedirection of the meridian, and the chart will be adjusted tothe cardinal points.”

The great length to which our extracts from Monge’swork have extended, will be, we trust, pardoned, in consi-deration of the value of those extracts ; and of our desire todo the most ample justice to the learned and ingenious author.Though many works of a similar kind by eminent writershave since issued from the press, the Geometrie Descriptive of Monge still holds a most distinguished place; and will con-tinue to be regarded as one of the best elementary books ofmodern times.

DESICCATION, (Latin , desicco, to dry), the act ofmaking dry; it is the chemical operation of drying bodies,and is effected in different modes, according to the nature ofthe substance. The term, Desiccating Process, has beenapplied to a patented invention, (Davison and Symington’sPatent), for seasoning or drying a great variety of sub-stances. It is said to have been used with success in season-ing wood.

DESIGN, ( designo , Latin ; dessein, French ), an originaldrawing of a building to be executed, comprehending theinvention, composition, and arrangement of the whole. Adesign includes plans, elevations, and sections of the buildingintended to be carried into execution, besides other drawingsof details, or parts at large. The number of these will, ofcourse, depend either upon the nature of the building, that is,on its being more or less complex, or as it is intended to showit more or less fully. A small simple house will only requireone plan and an elevation. A large edifice, with great varietyof parts, will require plans of each story, elevations of thedifferent fronts, a longitudinal and transverse section, and, ingeneral, as many drawings as will be sufficient to explain allthe parts. All the minute parts, as bases, capitals, architraves,friezes, cornices, and other mouldings, are to be exhibited intheir true geometrical proportion, at full size.

There is, perhaps, a certain prejudice against drawings ofthis kind, from an impression too generally entertained, thatthey are unintelligible except to the initiated. This feelingwould be easily removed, were unprofessional persons to takethe pains to examine a complete set of well-prepared architec-tural drawings. A very little explanation renders these draw-