§84 SURVEY OF THE COAST 



quaintcd wiili these subjects, as to render such description 

 unnecessary. Plate IV. presents both a horizontal and ver- 

 tical view of the whole apparatus, as when actually employed 

 in the measurement. 



The safe transportation of the boxes between their placing 

 and removal, from under the microscopes, will requiie con- 

 siderable care, and also an arrangement to prevent the box 

 from being put out of shape, in carrying it upon uneven 

 ground, and by which in an extreme case even the bars 

 might lose their contact. It will therefore be proper to ad- 

 just these bars, in case of any suspicion of this kind. 



There being two complete sets of instruments in the col- 

 lection intended for the survey, and a case seldom occurring 

 in which l)oth sets shall be employed at the same dme, it may 

 be convenient to use more than one full set in an operation. 

 For instance, take more than three microscope stands. For 

 greater security, take the directing telescope of tlie set not 

 in use to make the back verifications of the line, by placing 

 it at the other side and end of the box. Take additional rol- 

 lers, thermometers, changes of legs, tripods, ^c. ^c. 



The manner in which the journal of the measurement of 

 a base line should be kept requires minute care, on account 

 of the great number of observations and remarks to be in-^ 

 serted. 1 would here give a sketch or extract of such a jour- 

 nal, had I completed the measurement of a line with ths appa- 

 ratus ; but the survey of the coast was interrupted before this 

 could be effi-cttd. I shall however insert a few remarks, 

 which occurred to me in Switzerland, when measuring with 

 Mr. Tralles. now Member of the Academy of Berlin, in 1791 

 and 1797, a base line of alwut 42000 feet in length, and upon 

 which the triangulation was founded. This base was mea- 

 sured twice : first, with a chain similar to that made by 

 Ran\sden for the Rnglish survey, — and secondly, with an ap- 

 paratus of four toise bars, somewhat similar to that above de- 

 scrilied. 



1 shall place these remarks under the following heads : — 



