392 Proceedings of the British Association. 



and one minimum in the mean daily curve, which corresponds nearly 

 in epoch with the principal maximum and minimum of the curve for the 

 entire year. In the winter months, on the other hand, there are three max- 

 ima and three minima, the evening maxima appearing to break into two. 

 The epoch of the morning maximum moves forward as the time approach- 

 es the winter solstice, appearing to depend upon the hour of sunrise, which 

 it precedes by a short interval. The epoch of the principal minimum is 

 nearly constant throughout the year. The daily range is greatest in the 

 month of July, when it is about "0045 of the whole intensity ; it is least 

 in the month of January, being then about -0008 of the whole. 



Total intensity and inclination. — The total intensity appears to vary 

 very little throughout the day. It seems to be least about 9 A. m., and 

 then to increase, attaining a double maximum in the afternoon. The 

 total range, however, being very small, the variations of the two com- 

 ponents of the intensity are dependent chiefly upon the changes of the 

 inclination. The inclination is greatest between 10/t. and 10/t. 30m. a. m. 

 and least about 6 p. m., the epochs corresponding with those of the least 

 and greatest values of the horizontal intensity. The daily range is 

 about two minutes in the early part of the year, and increases to more 

 than double of that amount in summer. If we combine the changes of 

 declination and inclination, the former being multiplied by the cosine of 

 the absolute inclination, we obtain the whole movement of the north 

 end of the magnet in free space, or the curve formed by the intersec- 

 tion of the magnetic axis with the sphere whose radius is equal to unity. 

 The whole movement during the first six hours of the day is inconsid- 

 erable. It appears, on a review of these facts, that the diurnal changes 

 in the direction of the magnetic force are (as might be expected) con- 

 nected with the diurnal movement of the sun, and its times of rising 

 and setting. The changes of the intensity appear to be influenced in ad- 

 dition by some other cause, or by the same cause operating less directly. 



Prof. Wheatstone made a Report on the Electro-Magnetic Meteoro- 

 logical Register, constructed for the observatory of the British Associa- 

 tion, which was represented as nearly complete. It records the in- 

 dications of the barometer, the thermometer, and the psychrometer, ev- 

 ery half hour during day and night, and prints the results, in duplicate, 

 on a sheet of paper in figures. It requires no attention for a week, du- 

 ring which time it registers 1,008 observations. Five minutes are suffi- 

 cient to prepare the machine for another week's work ; that is, to wind 

 up the clock, to furnish the cylinders with fresh sheets of paper, and 

 to recharge the small voltaic apparatus. The range of each instrument 

 is divided into 150 parts ; that of the barometer comprises three inches, 

 that of the thermometer includes all degrees of temperature between 

 — 5° and -[-95°, and the psychrometer has an equal range. 





