158 
of a delicate Galvanometer, a large deflection is observed 
when the axis of rotation forms any considerable angle with 
the line of magnetic dip. On first trying the instrument I 
perceived that its sensibility was such as to promise an 
extremely sensitive means for measuring the dip. Accord- 
ingly, soon after I had a small and more portable instrument 
constructed for this special purpose ; but up to this time I 
had not given it any sufficient trial. On the occasion of a 
recent visit, Dr. Joule assisted at some experiments with this 
instrument. The results have convinced us both that it 
will be quite practicable to improve it so that it may serve 
for a determination of the dip within a minute of angle. 
I hope, accordingly, before long to be able to communicate 
some decisive results to the society, and to describe a con- 
venient instrument which may be practically useful for the 
observation of this element. 
* Further Remarks on the Galvanometer/’ by William 
Jack, M.A., Professor of Natural Philosophy at Owens 
College. 
Dr. J oule’s results, given in the last number of the Pro- 
ceedings, suggested to me to inquire whether the ordinary 
formula which I gave in my last communication allowed a 
deviation of different sign for a short magnet and for one 
of considerable length. When the needle is at the centre 
of the circle, the formula gives, putting 
= n , and sin 2 ct = x, 
r 2 
and making some simple transformations 
64 E-r.tana ( 
( 31 5g + 12(h 
A 180.315 , 
' 84 87696) 
oi \ 
945 ' 2t n 
\ 945 > 
945 2 1 
: 315 315* j 
- E F 
