Some observations of the diurnal variation of the magnetic declination at Cuajimalpa near the city of Mexico

The following observations were made on September 15, October 1 and 15, November 1 and 15, and December 1 and 15, 1902, at Cuajimalpa, situated about 11 miles southwest of the City of Mexico. The approximate geographical position of the station is: latitude, 19° 20′N., and longitude, 99° 13′ or 6 h 37 m , west of Greenwich. The observations on the first four days mentioned were obtained with an Elliott magnetometer, whereas in those on the last three days a Mascart declinometer was used, referring the readings to the Elliott magnetometer. The mean results are contained in the following table. The mean of all the hourly readings gives the value D = 7° 27′.56 East. By subtracting this mean from the hourly values, the figures for the diurnal variation in the last column were derived, the sign + meaning hence an excursion of the needle to the east of the mean position.