IPS- 



Snccefs of the 

 inftrument. 



Probable future 

 advanta|;es. 



Method of con. 

 netting all the 

 obferved angles 

 in one com- 

 inon centre. 



Application of 

 the procefs. 



Inaccuracy to be 

 (jxpefted from 

 an inexperiened 

 ebferver. 



AEROSTATIC MACHIfJES. 



This inflrument, arranged in the manner here defcribed, 

 produced every defired efkGt in our experiments. The ii » 

 vention, as fimple as it is happy, may become very important 

 from the ufefiil applications of which it is fufceptible; and there 

 is already reafon to hope thai, by bringing this to perfection, 

 or by the formation of feme analogous inftrument hereafter, 

 there will be a poffibiiity of executing trigonometric operations 

 with much corre6tnefs, by the afliftance of aeroflatic machines^, 

 notwithfcanding their continual motion. 



It was not enough to have difcovered the means of conneclri 

 ing the angles with the plane of the horizon: it was ftill de- 

 firable, that all the angles obferved during afcents in any one 

 place, fliould have a relation to the common centre of obfer- 

 vation. To accomphfti this, it was necefTary to keep a regifter, 

 by fome means, of the (ituation of the machine at the precife 

 moment of meafuring each of thefe angles. This was done by 

 dropping from the aeroflat, at that inflant, a fmall flake, leaded 

 and furnitiied with an iron point. This flake fell rapidly to the 

 earth, into which it ftuck, and marked a point correfponding 

 to the fummit of the angle meafured. It was then eafy to 

 compare the pofition of 'this point, with that of one taken for 

 the common centre of the obfcrvation, and thence to deduce 

 the neceflary corre6lions. It muft however be noticed, that 

 the flake, when abandoned to itfelf, acquires, at the inflant of 

 its fall, a compound motion which partakes of that of the 

 aeroftat, and confequently is not exaclly vertical; but the er- 

 ror which refults from this deviation is but flightly perceptible 

 in pra6tice. 



The calculations and ordinary procefles of defcriptive ge- 

 ometry will furnifli all the means of making ufe of thefe differ- 

 ent obfervations, and of expreffing the refults on paper; not 

 only for their application to the conflruftion of maps, but alfo 

 to afcertain heights compared with the level: but we fliall 

 not in this place enter into any details on that head. 



The obferver engaged making thefe firfl experiments, 

 foon perceives that the involuntary embarraffment, occafioned 

 by the novelty of his fituation, when he finds himfelf infulated 

 and fufpended at a height of feven or eight hundred metres, 

 has' a confiderable influence both on the fidelity of his ob- 

 fervations and on the time necefTary for making them. All 

 pertjiinty depends^ in fad, upon the confidence and readinefs 



of 



