1881.] 5*55 [Chase. 



noou, making the total range .00123). The arithmetical mean of any cu- 

 mulative disturbances which are occasioned by the accelerations and retar- 

 dations of alternate half-daily fall towards and rise from the Sun, should 

 occur at 12h ~- l/5~from midnight, or at 8h. 29m. A.M. and 3h. 31m. P.M. 

 These hours correspond very nearly with those of mean disturbance, both 

 in the horizontal and in the total force : 



Noon. 12 P.M. Mean. Time of Mean. 



H. F. +.001099 —.000481 +.000809 8h. 31m. A.M.; 3h. 16m. P.M. 

 T. F. +.00095 —.00043 +.00026 8h. 45m. A.M.; 3h. 42m. P.M. 



The greatest observed deviation from the theoretical times is 16m, in 

 the morning mean of total force ; the least, 2m., in the morning mean of 

 horizontal force. The mean deviation of horizontal force is 8.5m. ; of total 

 force, 2.5m. 



121. Lunar Daily Gomparison. 



The lunar disturbances, both of the barometric and of the magnetic means, 

 are of a higher order than can be accounted for by mere disturbances of 

 weight or pressure, or by any pther known activity of our satellite ex- 

 cept the accumulation of energy in currents (t^). We have no reason to 

 think that the moon exerts any specific chemical (/5), luminous (y), or 

 thermal (8) influence of her own, but her tidal disturbances of the elas- 

 tic or quasi-elastic currents of the rotating earth (s ^ tj) are very impor- 

 tant. 



Schiapparelli, Loomis and Chase have shown that long-continued ob- 

 servations, at various stations, demonstrate the existence of an evident 

 lunar influence on the precipitation of rain, and, consequently, on the elec- 

 trical condition of the atmosphere. Each station has an "establishment" 

 of its own, which can be determined, where the meteorological conditions 

 are most uniform, by observations extending over a period of three or 

 four years. This influence, which is undoubtedly due to tidal disturb- 

 ances of atmospheric currents, is further shown in the lunar modifica- 

 tions of the direction and velocity of the wind, which have been pointed 

 out by M. Bouquet de la Grye.* 



Both in the lunar and in the solar tables the critical periods of horizon- 

 tal and total force are nearly synchronous. In the lunar variations the 

 vertical force increases as the horizontal force diminishes, and vice-versa. 

 Each of the lunar magnetic tides is of the same general character as the 

 oceanic and atmospheric tides. The lunar horizontal force and total force 

 are greatest and the vertical force is least when the barometric currents are 

 moving most rapidly away from the Earth's centre ; the horizontal and 

 total force are least and the vertical force is greatest when the currents 

 are moving most rapidly towards the centre. 



The range of lunar disturbances of vertical force (from + .000072 to 



* Comptes Rendus, Isxxviii, 345-8. 



