[ no ] 



have the accuracy which in aftronomical ufe, and like circum- 

 ftances, the plummet affords. 



It is eafy to conceive that the greater the fize of this level is made in length, 

 when it is conftrufted in the form in fig. 8, the more accurate will it be, and fteady 

 in reCfting the agitation of the wind. Alfo that this fafhion of it admits the more 

 eafy adjuftment, as the mirror can be turned quite round on its axis, and the 

 higheft and loweft place of the image inftantly difcovered, confequently its error, if 

 it has any. 



