98 



The principal minimum at 14 10 Makerstoun mean time. 



A secondary maximum at 20 SO 



A secondary minimum at 22 50 



The principal maximum at 5 30 



A third minimum at 12 10 



A third maximiun at 13 10 



The third maximum and nunimum are but faintly marked. The 

 form of the diurnal curve, and the periods and number of maxima 

 and minima, vary throughout the year ; neglecting the inferior 

 maximum and minimum, the diurnal curve is single in winter and 

 double in summer, the principal minimum occurs at noon in summer. 



The diurnal range is greatest at the equinoxes, and least at the 

 solstices, the range at the former being nearly two and a half times 

 that at the latter. 



Each of the mean values of the vertical component at 21*^ and 

 O'' , is nearly equal to the mean for the year. The secular varia- 

 tion is negative. 



The investigation for the relation of the variations of the vertical 

 component to the moon's hour angle, gives for the mean of the two 

 years 1844 and 1845 — 



The principal minimum about 5 hours before the moon's passage of the inferior meridian. 



The principal maximum about 3 hours after 



A secondary minimum about 4 hours before superior 



A secondary maximum about 1 hour after 



The results for each year differ little from the mean of both ; the 

 secondary maximum and minimum are not so well shewn in 1844 

 as in 1845. The observations of single months, when free from 

 magnetic disturbances, have been found to give the same periods. 



Investigations were made for a period connected with the moon's 

 phase or synodical revolution ; each of the years 1844 and 1845 

 indicates maxima of the vertical component near the quadratures, 

 and minima near the syzygies. 



4. Two Verbal Notices. (1.) On the Geology of Arthur 

 Seat. (2.) On the Dentition of the Walrus. By the 

 Rev. Dr Fleming. 



(1.) Dr Fleming read the following passage from Townson's 

 " Tracts and Observations in Natural History," Edin. 1799, when 

 treating of the " Rocks in the Vicinity of Edinburgh :" — " The first 

 of the chains or ranges of rocks that I lately described, as lying at 



