744 



J. A. BROUN ON THE LUNAR DIURNAL VARIATION OF 



tions in the different weeks, the differences due to the lunar action (and irre- 

 gular causes) were arranged in columns under the lunar hours to which they 

 respectively belong, as in the following scheme, where the short lines indicate 

 the + or — differences.""" 



Lunar 

 day. 



H. 







H. 

 1 



H. 



2 



H. 



3 



H. 



4 



H. 



5 



H. 



6 



H. 



7 



H. 



8 



H. 



9 



H. 



10 



H. 

 11 



H. 



12 



H. 



13 



H. 



14 



H. 



15 



H. 



16 



H. 



17 



H. 



18 



H. 



19 



H. 



20 



H. 



21 



H. 



22 



H. 



23 



H. 



24 



H. 







1 



2 

 3 



4 

 5 

 6 

 7 

 8 

 . 9 



1° 



28 









— 



— 







1 









— ' 





— 





— 



— 









The first difference under h. with which the lunation begins is that derived 

 from the observation made half an hour after noon (the lunation always begin- 

 ning with the new moon), and corresponding to the moon on the meridian. 

 The difference under 6 h. in the first lunar day corresponds to after sunset, while 

 that under 17 h. corresponds to before sunrise. Thus the differences before and 

 after sunset are separated by a light zigzag line, while those before and after 

 sunrise have a thicker zigzag between them. 



It is obvious that, if each horizontal line represents the lunar diurnal varia- 

 tion during a lunar day, and if this variation obeys the same law, or nearly the 

 same law, throughout a lunation, it does not matter how we obtain the means 

 from the vertical columns of differences ; and the means obtained from the 

 night hours (those within the zigzag lines commencing with 6 h. to 17 h.) should 

 give the same result as those to be obtained from the day hours. If, however, 

 the law varies with any argument, such as the moon's declination or phase, this 

 will be proved by a comparison of the results for different lunations in different 

 months of the year. 



* It will be seen in the scheme that the lunar day has been considered equal to 25 hours (it is equal 

 to 24 h. 50 m. nearly), and consequently the lunar hour angle is equal to only 14°' 4. Also h. is 

 repeated in the last column. This was always done in order to find the correction due to changes of 

 mean declination, which caused the variations to increase or diminish from the 1st to the following h., 

 especially in means derived from limited series of observations. It was found ultimately that it would 

 be preferable to repeat 1 h., and perhaps even 2 h. in order to obtain this correction with more accuracy. 

 Other details as to the precautions taken in these discussions will be found in the first volume of 

 Trevandrum Observations. 



