174 Lieut. Foster’s observations on the diurnal changes 
indications of such changes having taken place ; and it is only 
on these occasions, that the expression for the magnetic in- 
tensity of the horizontal needle is at variance with the irregu- 
lar motion of the neutralized needle. 
On looking over the observations it will also be seen, that 
when the north end of the needle was directed to the south- 
ward, between N. 85° E. and S. 85 0 W. its motion during the 
time of westerly daily variation was generally towards the 
left hand, but when directed to the northward, between N. 85° 
E. and S. 85° W. its motion was then most commonly to the 
right hand (see the figure in Plate IV.); and that when held 
between N. 85° E. and north, a greater daily change ob- 
tained than at any of the other positions, amounting in one 
instance to 50 degrees ; but when directed to S. 85° W. no 
daily variation, or at least a minimum, exhibited itself. 
With respect to the effect produced on the needle when 
held between N. 85° E. and north, it appears, from observa- 
tions on the times of vibrations of a horizontal needle, that an 
increased intensity generally took place about noon, at which 
time also, the maximum westerly daily variation generally 
happened ; and as we have already seen, that the motion of 
the north end of the needle in this position, during the time 
of westerly daily variation, was to the right hand, or towards 
the magnetic meridian, the effect of an increased intensity 
would be to draw it still further in that direction, and there- 
fore, produce the extraordinary amount noticed. But with 
the north end of the needle, held between S. 85° W. and 
north, where its motion is still to the right hand at the time 
of westerly daily variation, the effect of increased intensity 
then, would be to draw the north end of the needle to the 
