AEROSTATIC MACHINES. 199 



ef Uie obferver; and it cannot be concealed, that it may 

 produce great inconveniences, becaufe this difficulty of ope- 

 rating opens wide limits for the errors which it is poffible to 

 commit. 



From this laft obfervation it will be feen: ift. That it is in- CondUions ne- 

 difpenfably neceflary to have acquired a great aptitude for thefe ^^^ycQ obfer- 

 fort of obfervations, to be able to execute them with precifion : vations. ' 



2d. That the procefTes juft defcribed are more fatisfadory iri 

 theory than they would be in thofe applications which require 

 firict accuracy; and, that though there are lituations in 

 which nothing can be fubftiluted for their ufe in the conftruc- 

 tion of fome figured plans, it is at leaft proper never to ufe 

 them in preference to thofe means of obfervation which are 

 better known, and which can be employed with more cer- 

 tainty. 



But it cannot be too often repeated, at the fame time, that Advantages t* 

 aeroftats furnith the means of giving the moft lively intereft to f"^^^ ^l^^ 

 the delineation of the figure of the earth, in maps of all de- loons in lurvey- 

 fcriptions; and tliat their ufe is of the greateft affiftance in the '"S coantnes. 

 formation of plans, the outline of which may be fufficiently 

 defined by a fimple eye-fketch. The aerial obferver, by 

 difcovering a vaft extent of country, accuftoms himfelf fully 

 to confider the general organifation of the afperities of the 

 country, and even the particulars of its varieties, as well 

 as the tone of colour, which appear to give a different charac- 

 ter to each portion of territory. If this new method of obfer- 

 vation be cultivated with affiduity, it will doubtlefs lead to a 

 fenfible improvement in the art of drawing plans. But to be- 

 nefit by the advantages which it affords, it is neceffarv, that 

 thofe who are deflined to this employment fhould join a pro- 

 found knowledge of geometry to a great facility in defigning 

 landfcapes. May they be convinced of the importance of this 

 truth, and affure therafelves that no part of the plan can arrive 

 at perfedtion, either ornamental or relative to civil and mili- 

 tary purpofes, unlefs ftri6l accuracy in the outline is accom- 

 panied by that fidelity of expreffion which is capable of pro- 

 ducing in thofe who infpe6l the plans, all the ideas which the 

 obferver had formed from the afped of the country. 



From all that has been faid, we may conclude, that tho aero- Valuable pro- 

 ftaticartcombinespropertiesnolefs valuable than unqueftionable perties pofleffed 

 in topographic operations and military relearchesi that its per- chines. 



fedion 



