22 



MAGNETICAL OBSERVATIONS. 



OBSERVATIONS AT SAN ANDRES CHALCHECOMULA. 



Description of Station No. IV. — The town of San Andres is situated in a plain 

 at the foot of the Peak of Orizaba, and this volcano rises, to the east of it at a 

 distance of about ten miles, to the height of 10,000 English feet above the plain, 

 which is elevated 7,800 English feet above the level of the Mexican Gulf. 



The instruments were mounted in the yard of the house of Mr. Canto. The 

 azimuth of a very distant tree (A) was originally determined by observations of 

 the sun, but after the declinometer had been mounted this tree was obscured by 

 fog, and the magnetic azimuth of another, nearer mark (B), having nearly the 

 same direction as A, was determined. Afterwards the angle between A and B 

 was measured and found A 32'. 3 to the right of B. This quantity has to be 

 added to the circle readings of B to get the corresponding readings for the mark A. 



Deflections have not been observed at this station. 



Station No. IV. San Andres. 

 Latitude 18° 59'. Longitude 97° 15' W. of Greenwich. 



