Royal' Society. 341 



At Singapore, the extreme Avesterlj' variation occurs in December 

 at 19 iiours, or 7 a.m. ; in January at 20'' ; in February at 21^ ; in 

 Marcli, or the month in which the sun passes the equator, there is a 

 slight retrogression ; in April the extreme westerly variation is at 

 21''; in July and August at 23'' ; in September at 22'* ; in October 

 at 21 ^ and" in November at 20 hours. In the winter the extreme 

 westerly variation is at 20 hours ; in spring at 21 hours ; in summer 

 at 23 hours, and in autumn at 21 hours ; agreeing in this respect 

 witii the spring curves, but differing very materially as regards the 

 progression of the needle eastward in the afternoon. The oscillation 

 has much the greatest range during the winter months ; autumn 

 comes next, and preserves an almost perfect parallelism with the 

 winter. The spring and summer curves preserve their parallelism 

 during the afternoon. '■ '' i ■!''■' ■ 



The mean curves of each of thfe three years have an almost perfect 

 resemblance. There are two most decided maxima at 18'' and at 3 

 or 4' hours, and one minimum at 21''. There are besides two other 

 minima at 10'' and 17'', and another maximum at I4< hours, making 

 in all three maxima and three minima. If we turn to the seasons, 

 wc find in the winter only one strongly defined maximum and mini- 

 mum. In spring two maxima, ()ne minimum ; in summer and autumn 

 two maxima and two ndidma. The amount of oscillation is greater 

 in winter than in summer. The sun is a longer time to the south 

 of the line of minimum force than to the north of it. Singapore is 

 in north latitude 1'^ 18', and the lines of no dip and minimum force 

 cross the meridian of Singapore in latitude 8° north nearly, and 

 therefore the sun is to the south of ' these lines about 220 days of 

 the year. If we compare the oscillations of tiie declination at the dif- 

 ♦■•^rent stations with the Singapore curves, wc see that of the sixteen 

 stations two do not agree, one is doubtful, and the other thirteen do 

 agree with the march of the needle at Singapore. Of the three not 

 in accordance, the one that is doubtful is in the vicinity of the lines 

 of no dip and minimum force, Mliilst the two which do not agree, 

 viz. Madras and Moulmein, are both to the north of the line of no 

 dip, and of the line of minimum force. The Moulmein observa- 

 tions were made in the month of April; the hours of morning maxi-' 

 mum and niininuim are 21 and noon, whereas at Singapore the hour 

 of morning minimum is 21, which is that of the maxinmm at 

 Moulmein. Again, the Madras observations were taken in the 

 autumn, the morning maximum and minimum being at 20 hours 

 and at noon ; there is no well-defined morning maximum at the 

 same period at Singapore, but the morning minimum occurs at 21 

 hours. We see, therefore, that the stations south of the line of no 

 dip and of mininuuu force, with the exception of Keemnh in the 

 Celebes, all are in ))erfect accordance with the march of the needle 

 at Singaport!. Sandjooanga, in the island of Mindanao, is nearly 

 on the line of no dii), and agrees generally with the Singapore 

 curve; but it is to bo observed, that as wc proceed northerly and 

 approach the lines of no dip and of minimum force, the similarity 

 to the Singapore curve becomes much more ftxint, although agreeing 



