746 J. A. BROUN ON THE LUNAR DIURNAL VARIATION OF 



Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 



Area f Day, 6"20 3'-05 2'-96 2'-59 l'-66 2'-25 2'-18 2'-23 l'-94 l'-01 2"34 4-47 



observed, \ Night, 1'39 l'-45 l'-60 1'17 0'-85 0'-60 0' 98 0'-85 1'07 l'-23 1"26 l'-44 



Ratio, jAv 4-5 21 1-9 22 2-0 3-8 2-2 2-6 1-8 0-8 1-9 3-1 



Ranges J Day, 0'-85 0"38 0'-43 0'-35 0'-20 0'-31 0'-35 0'-27 0'-29 0"17 0'-37 0'-64 

 calculated, { Night, 0'- 20 0'-22 0'-19 (M8 0'13 0'-07 0'14 0"09 0'-16 0'-16 0'-20 0'-20 



Ratio, ^^ 4-2 1-7 22 1-9 1-5 4-3 2-4 30 1-8 11 18 3-1 



Area f Day, 6'-29 3'-06 2'-95 2'-60 l'-33 2'-22 2"16 2'-08 l'-86 0'-98 2'-37 4'-39 

 computed, (Night, l'-25 l'-41 l'-56 l'-20 0'-80 0'-49 0'-97 0'-61 0'-99 1'12 l'-13 l'-39 



Ratio, tft~ + 50 2-2 1-9 2-2 17 45 2-2 34 1-9 0-9 2-1 32 



' JNiglit) 



The computed ratios are probably the nearest to the truth, as they are free 

 from the irregularities due to accidental disturbances. From the ratio for the 

 areas of the computed curves (for which the sums of the co-ordinates are 

 employed) the day is to the night as 5 to 1 in January, and as 4| to 1 in June. 

 The ratio is least in May and October, the two months in which the curve be- 

 comes inverted, the day and night areas for the latter month being nearly equal. 



29. This is a fact which is wholly independent of the question as to its cause, 

 whether connected with the varying positions of the moon or not. The law of 

 variation, however, for the day hours in each month of the year is so consistent, 

 that it becomes exceedingly probable that the change of law previously found 

 as apparently connected with the moon's varying declination is chiefly, if not 

 altogether clue to this cause (the different action in sunlight and in the shade 

 of night). The law deduced from the night hours shows a variation of such 

 small range, that it is comparatively more affected by the irregularities due to 

 change of the daily mean declination and other causes. 



30. If the law of lunar diurnal variation really depends on the moon's position 

 in declination, then the method just described will give results, in which some of 

 the diurnal curves for any month will be made up of the parts of the curves 

 belonging to the day hours for the moon's different positions, and others to the 

 parts belonging to the night hours. We can, perhaps, best judge to what extent 

 the moon's declination (or longitude) is connected with these results by an exami- 

 nation of the projected curves derived from the discussion for the moon's 

 declination."- 



Thus, to begin with January, the curve for the week with the moon farthest 

 north shows the maximum of easterly declination, which happens near the 



* Postscript. — When this was written it was intended to give the projected curves for the different 

 positions of the moon in declination ; this the Postscript (43) and the Plate (XXVIL), with curves for 



