O PORTABLE BAROMETlfiR. 



ally traverse it. The contrary is however the case, and the 



small niimber of observations of this kind may he attributed to 



Caiisps. TJie several causes. The instruments are of considerable expcnce, 



instmineiits f^,^(] jY(>ni their Complicated construction easily liable to be out 



;iie costly, lia- , . , , . mi i 



l)le to be'de- ^'^ order in the course ot a hmg journey. The observations 



raiiEfed.aiidthe themselves, though each not taking up any very long time, yet 



demand time ^vhcn multiplied on cvcr\ hill and valley, as they ought to be, 



and care. foi- tlje purpose of obtaining a just idea of the country survey- 



cfl, ir. the aggregate consume much of the traveller's time, 



and the constant unpacking and repacking the instrument be- 



( o^n■'^ a greater labour than our natural indolence easily sub- 



mirs fo. 



Tuu o'osfrvris 'It has moreover been generally supposed, that two instru- 



rnstrmi'ciirs ^ nio'.Us and two observers making simultaneous observations at 



have {Toiiejaiiy ihc upper and lower stations of the height to be measured, are 



i'tc"'^.saiv^^''^''^-''^*^'''i"''^'''^'*'y "^f-'c^sf^'T- 1'^'^ ^f course would put it out of 

 tlic power of a solitary traveller to make any observations at 

 II n. Whclher from these or other causes, the fact is, that 

 3^cnoc it is that whoever reads the numerous tours, surveys, and reports of dif- 

 aiid Impressions ^'^'''^^'- P^'"^^ *^^ !°^"' ^^^^^^^ published within these last twenty 

 of the tr.ce of years, alid many of them professedly with a view to science, 

 of\f'Wi utility ^'^^^'^^' °^ agricidture. mineralogy, ov geology, will be perpetu- 

 ond interest, ally disa])pointed by meeting widi mere guesses at the eleva- 

 ted in ti^'veir""^'^"^ ^^^ ^''^ tracts of country descriix'd, though a knowledge of 

 those elevations is almost indispensable to the geologist, miner- 

 alogist, and military surveyor, — highly useful to the scientific 

 agriculturist, and very interesting to every one who from mere 

 motives of enlarged and enlightened curiosity reads books of 

 travels, or employs his own leisure in traversing the countries 

 described by other voyagers. 

 The impedi- 1 cannot therefore but hope, that by simplifying the baro- 

 vSion^^'ro^^o-"^'^^*^''"' ^""^ thereby rendering the instruancnt much less cx- 

 sed to be le- pensive and its use at the same time more easy, and shewing 

 plifsinff the™' ^^^^ ^^'^ considerable accuracy may be attained by a single 

 instrument and observer, this most useful branch of science may be cultivated 

 tinT^oli^erver ^^ ^° ^^'^^^ ^" extent, that in the course of a few years we may 

 may obtain va- have almost as perfect an idea of the relative heights of the 

 luable results, ^(jfl-pj.^.,,^ p^,.^^ ^,C' |.;jigiand as we now have of their horizontal 



distance. 

 Portable baro- A baruiuclcr, ncarlv similar to that which 1 am now about to 

 meter of Dr. ' describe 



ion. " 



