l64) MEASUREMt-VT OF \N ARC ON THE 



The angles in general have been taken three and 

 four times, and every time that the object was ob- 

 served, both microscopes were read off thrice, and 

 two separate field books kept for making out the 

 angles. What are here recorded, are the means 

 taken from the two books. In case a difference in 

 those angles, noticed at the time, left any reason 

 to suspect an error in the instrument, the division 

 between the dots was carefully examined, as well 

 as those to the right and left, and if any error was 

 discovered, allowance v/as made accordingly. 



SECTION V. Triancles. 



North End of the Base from the South End of the 

 Base 40006,4. 



