Lovering and Bond on Magnetic Observations at Cambridge. 9 
the table; the chord at right angles to the magnetic meridian 
is the projection of the scale which is read in the observations ; 
Cis a Gauss Magnetometer which is fitted up after the style of 
those at the Gottingen Observatory. The three circles at Care 
the feet of three posts, ten feet long, which unite at the top eight 
feet above the floor and give a stable point of suspension to the 
needle. The rectangle, enclosed within the feet, is the box which 
surrounds the magnet and protects it from currents of air. Within 
the box may be seen this magnetized bar in the magnetic meridian, 
with a mirror firmly fixed to its south end to reflect the scale at D 
into the tube of the Variation-Transit. The bar is suspended by 
a copper wire silvered, 0.011 of an inch in diameter, 5 feet 6 inches 
long, and with its fixtures weighs about 3 pounds. 
From this arrangement it follows, that as the bar varies in its 
position it must carry the mirror with it. The place of the mirror 
determines the mark on the scale which is reflected into the centre 
of the telescope ; so that as the reflecting surface moves the marks 
of the scale that are successively seen are read off and employed 
to ascertain the motions of the bar. The scale at Cambridge is 
so divided that the angular motion of the needle is read directly 
from it without any reduction. This novel mode of observing 
changes of magnetic Declination is a great refinement upon the old 
methods, and has given an accuracy to the determination of this 
magnetic element which has hitherto been considered attainable 
only in astronomy. For a more minute description of the Gauss 
instruments and the directions to be obeyed in observing with them, 
the reader is referred to Taylor’s Scientific Memoirs, Parts V. and 
VI. It is necessary to omit in this place any further details except 
such as are required in order to understand the remarks which fol- 
low. As all the observations embraced in this paper were made 
2 
