78 Dr. E. Obach on an Improved Constniction 
of Messrs. Siemens Bros. & Co. at the same time enables me 
to place the instruments before you for inspection. 
Ere proceeding further, allow me to say that I shall not on 
this occasion touch upon the theory of the instrument, which 
is already given elsewhere, but confine myself wholly to de- 
scribing the recent improvements in its construction, adding 
a few series of measurements in order to prove the high degree 
of accuracy obtainable. 
I propose to deal with the different parts of the instrument 
under separate headings; and will first speak of 
The Magnetic Needle akd its Pointer. 
The older instruments had a flat magnetic needle fixed to a 
light vertical axle, pivotted at both ends between jewels to 
prevent any dipping, which the needle would otherwise expe- 
rience with great inclinations of the ring. This arrangement 
answered sufficiently well with ordinary care; but still the 
delicate pivots were likely to be damaged, thus impairing the 
sensitiveness of the needle. As now constructed, the dipping 
of the needle is completely avoided in the manner illustrated 
by the annexed figure. The needle, n s, is fixed to a thin 
Half nat. size, 
its upper end, the lower end of the 
axle being provided with a cylindrical brass weio-ht, w. This 
weight offers but little additional momentum to the whole 
system round the vertical axis, whereas the movement round 
the horizontal axis is completely prevented. The aluminium 
