On the Use of the Pocket Box-Sextant. 57 



the apparatus, by which an active and intelligent officer has sur- 

 veyed large tracts of mountainous country, with the necessary 

 degree of accuracy and despatch required in such operations. 



Without depreciating the larger and truly valuable instruments, 

 the pocket-sextant may be safely recommended to such persons and 

 for such purposes as have been detailed, as a means of adding 

 much useful information to their journals, almost without an addi- 

 tional pound weight to their baggage ; but it is by no means wished 

 to be understood, that very scientific surveys are to be superceded 

 by this more simple method : practical accuracy is alone aimed 

 at and most certainly attained, but we do not go beyond that ; 

 and in pointing out the advantages of the pocket-sextant to mili- 

 tary men and travellers, the writer is desirous of making a marked 

 distinction between the practical results it produces, and the very 

 minute and hairbreadth measurements of a geodesical survey. 



To apply so small an instrument to astronomical purposes might 

 seem frivolous ; but, when it is considered that mere approxima- 

 tions are sometimes useful where greater accuracy cannot be 

 obtained, it will perhaps be conceded, that even this little instru- 

 ment will furnish useful information in the absence of those that 

 are more expensive and less portable ; particularly in difficult and 

 and dangerous journeys upon mountains, volcanoes, and other 

 places where heavy apparatus is not easily transported, and 

 very likely to be put out of order, or possibly rendered useless : it 

 was possibly for this reason among the instruments taken by a 

 late traveller up Mont Blanc. 



The following set of latitudes are inserted just as they came out, 

 in order to shew the utmost variations to which they are liable ; 

 all the corrections were applied as usual with capital instruments 

 and from the best tables, that the whole error might fall upon the 

 instrument and the observer. 

 1822. April 13, Regulas 51° 19' 23,8" 



28, SpicaVir 51 19 58.48 



29 51 19 58.08 



30 51 19 53.35 



