74 



DISCUSSION OF THE INFLUENCE OF THE MOON 



The coefficients are in decimals of scale divisions (1 div. 0.000087) parts of the 

 horizontal force) ; the angle a counts from the superior culmination, giving a curve 

 of which the general features are in exact accordance with those deduced from the 

 Philadelphia observations, viz : a principal maximum after Upper Culmination, fol- 

 lowed by the secondary minimum ; the secondary maximum after the Lower Cul- 

 mination, followed by a principal minimum. The times and amount of these values 

 are compared in the following Table X. 



Probable error of any single representation of the Philadelphia values = + O d .25 

 = +_ 0.000009 parts of the horizontal force = + 0.000038 in absolute measure. 



Investigation of the Horizontal Force in Reference to the Lunar Phases. The fol- 

 lowing process of reduction has been adopted : After marking the days of the full 

 and new moon, and also the days preceding and following, the daily means of the 

 horizontal force readings were taken (already corrected for difference of tempera- 

 ture and progressive change.) In the place of any disturbed observation, the 

 monthly normal, belonging to the respective hour, was substituted before taking 

 the daily mean. All accidental omissions in the record of the hourly or bi-hourly 

 series were supplied by the hourly normal of the month. The means thus obtained 

 are independent of the solar diurnal variation. The monthly normal was next 

 compared with each daily mean and the differences (normal minus mean) were 

 tabulated. 



A positive sign signifies a greater ; a negative sign, a less force than the normal 

 value. As the results deduced from a single year are yet too much affected by the 

 incidental irregularities of the observations, the collective results from the five 

 year series (1840-45) are herewith presented. 



