268 Observations on Surveying Instruments. 



Art. VI. — Observations on Surveying Instruments, and the 

 means of remedying their imperfections ; by Lucius Lyon, 

 Surveyor and Civil Engineer — {with a print.) 



Detroit, Michigan Territory, Jan. 26th, 1828. 



Magnetism is the well known name of a mysterious pow- 

 er, manifested only by its effects, and of whose ultimate 

 cause we are ignorant. 



Among its effects, none is more important, than that which 

 results from the application of one of its familiar properties, 

 to the art of surveying. 



By no other means at present known, can lines be run, 

 new lands be laid off, estates subdivided, their boundaries de- 

 fined, and the local position of places ascertained, with so 

 much facility as by the magnetic needle. To perform the 

 same services, in any other way, with any tolerable degree of 

 accuracy, would be an interminable labor. 



But, although the magnetic needle affords great facilities 

 for the practice of surveying, and in most cases is the only 

 means which it is practicable to employ ; it ought not to be 

 relied on as entirely correct. 



It is subject to many irregularities, to which our present 

 limited knowledge of the laws which govern magnetism does 

 not enable us to apply corrections. Although more than 

 three hundred years have elapsed, since Columbus, with 

 astonishment, discovered the variation of the magnet from 

 the poles of the earth ; little or nothing has yet been done 

 toward finding out its cause, or satisfactorily explaining the 

 reasons for the different variation at different places, or the 

 change of variation, at the same place. 



Great improvement has, however, been made, in the ap- 

 plication of the magnet to practical purposes, in the manu- 

 facture of magnetic needles, and in fitting them to the instru- 

 ments with which they are used ; as well as in perfecting the 

 form, and increasing the accuracy and convenience, of those 

 instruments. In this respect we seem to have improved more 

 than other nations, in proportion to the unsettled state of the 

 boundaries of extensive tracts of our lands, the newness of 

 much of our country, and the consequent necessity for using 

 surveying instruments. Of the truth of this remark, any per- 

 son who is a competent judge, and who will take the trouble 

 to compare American with English compasses,, will be 



