12 



horizontal force, and vertical force, magnetometers, — the barome- 

 ter, its height and temperature, — the dry and wet bulb external 

 thermometers, and the thermometers of the two force magnetometers. 

 To these were added observations of the weather. 



The magnetic inclination, or dip, has been observed since the com- 

 mencement, with a few exceptions, twice a-week. 



Since July 1841, the monthly periods, named Terms, have been 

 regularly kept. The terms are periods of twenty-four hours, which 

 occur once a-month, on days previously agreed upon, and during 

 which simultaneous observations of the magnetometers are made in 

 all the magnetic observatories. At present, the three magnetome- 

 ters are observed every five minutes of the 24 hours, meteorological 

 observations being made hourly. In this way, each term produces 

 388 observations of each magnetometer, comparable with the obser- 

 vations made at the same instant in the other observatories. 



Finally, observations for the absolute declination and absolute 

 horizontal intensity of the earth's magnetism have been made as 

 regularly as possible at different periods of the year. 



The second class of observations is irregular, and comprise all 

 those observations of phenomena which are irregular in their pe- 

 riods. The most important of this class are the extra magnetic ob- 

 servations. "Whenever the magnets are found to have assumed posi- 

 tions differing unusually from those at the previous observations, they 

 are watched, and if found to be moving, extra observations are im- 

 mediately commenced. Wlien the disturbance is moderate, the three 

 instruments are observed every five minutes, as on term days ; if it 

 be considerable, an instrument is observed every minute. 



Much attention has been paid to the magnetic disturbances in 

 1844. Upwards of 60,000 extra-readings of the magnetometers 

 having been made in that year, giving about 26,000 mean posi- 

 tions. 



The aurora borealis is as carefully observed as due attention to the 

 magnetic disturbance with which it has here been found invariably 

 accompanied, will allow. Attention is paid to the measurement and 

 description of halos, parhelia, and paraselenae. 



The reductions are at present in a considerable state of forward- 

 ness ; and it is expected that the volume for 1843 will be ready to 

 place in the printer's hands as soon as that for 1841 and 1842 is 

 issued. 



