67G 



MR J. A. BROUN ON THE DIURNAL VARIATION OF THE 



Variations for each Day in the Month of March. 



We are, as yet, still ignorant of the manner in which the law changes from 

 one form to another in March and October. In order to study this question, 1 

 have projected the hourly observations during several months. I shall give here 

 the projections of those only for January, February, and March 1859, a year of 

 considerable disturbance, and for the same months in 1864, a year of slight dis- 

 turbance. Plates XLII. and XLI 



An examination of these curves will show that the law of diurnal variation 

 does not pass regularly from one form to another in the month of March, either 

 by a sliding transfer of maximum to minimum, or by a diminution of movement 

 till the inversal takes place. On the contrary, there appears an utter absence of 

 continuity in any way : the curves are sometimes inverted from one day to the 

 next ; sometimes follow in part the law for January, in part the law for June ; 

 sometimes resemble wholly the one or the other ; frequently resemble neither in 

 any way : and this change appears to occur without order. 



The daily curves in March may be distributed into four categories. (I shall 

 include also the conclusions from the months of March 1854 and 1856, the curves 

 for which months I have projected, but which it does not appear to me necessary 

 to give here.) 



1st, Those curves, which resemble in some degree that for January, having a 

 minimum near 7 a.m., and a maximum between noon and 4 p.m. ; to this class 

 the curves for the following days belong: — 



1854, March 6, 7, 8 ? 18, 22. 



1856, „ 3, 4, 5, 6, 7, 19, 20, 21, 24, 29. 



1859, „ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 16. 



1864, „ 1, 2, 4, 5, 10, 15. 



2d, Those resembling the curve for June, in having the maximum about 7 a.m., 

 and a minimum near noon. To this class may be given the curves for 



1854, March 14, 16 ? 23, 24, 25, 27- 



1856, „ 11, 13, 15? 18, 31. 



1859, „ 19,26,28,29,31. 



1864, „ 7, 8? 11, 12? 17? 18? 25, 26, 29, 30, 31. 



3d, Those which approach the second class, but have the maximum near 10 

 or 11 a.m., and minima near 6 a.m., and 1 to 4 p.m., namely, — 



1854, March 9, 10, 11, 12, 13, 21. 



1859, „ 22, 25, 26, 27 (also April 1, 2, 3, 4, 5, 7, 8). 

 1859, „ 11? 12? 13, 14, 17, 18, 25? 30, 31? 

 1864, „ 17? 19, 21,23, 24? 



Mh. Those which resemble none of these, and happen on the remaining days 

 of each month (not including Sundays, when there were no observations). 



