60 MR. BROOKE ON THE AUTOMATIC REGISTRATION OF MAGNETOMETERS, 
is inserted in the opposite corner, that the lamp may, if necessary, be supplied without 
removal ; it will, however, contain more than enough for twelve hours’ consumption. 
The plane of the wick is inclined at an angle of 4° or 5° to the axis of the pencil of 
light, which passes through a slit 0-25 inch long, and O'Ol inch wide in the side of a 
copper chimney : the chimney is supported on glass feet, to prevent the heating of 
the camphine by conduction, and for the same purpose the burner passes through a 
piece of wood. As the burner may occasionally require a vertical adjustment, it 
passes through a small collar with a set-screw ; and as a minute quantity of resinous 
matter, resulting from the imperfect combustion of the camphine, will sometimes 
trickle down and interfere with the mobility of the collar, it is protected by a small 
concave rim attached to the burner. To prevent the escape of light from beneath 
the chimney, and also to protect the flame from the influence of slight currents of 
air, at the same time without excluding a due supply, a ring of metal is placed outside 
the glass supports, which rises about one-fourth of an inch above the bottom of the 
chimney. To render the combustion of the camphine more perfect, the draught in 
the chimney is confined by an obtuse conical diaphragm, having an aperture a little 
longer and wider than the burner, the exact size and position of which are repre- 
sented in Plate V. figs. 4, 5, 6. The small obliquity of the wick is for the purpose of 
accumulating as much light as possible in a narrow pencil. 
When the camphine is fresh, the lamp will burn for twelve hours without any 
deposition of carbon on the wick, or sensible diminution of the intensity of the light. 
The application of gas has not been attempted, as the apparatus would probably be 
applied in situations not accessible to the ordinary supplies of gas. For the purpose 
of actual observation, and especially wherever it may be proposed to obtain, not 
merely relative, but absolute determinations from the registers, it will be found 
desirable to detach the fine slit from the lamp, and to fix it by a suitable support to 
an immoveable stand on which the lamp is placed. It is also desirable that one edge 
of the slit should be adjustible by a fine screw, that the width of the aperture may 
be varied at pleasure # . 
The second object has been attained by a paper prepared with the bromide of 
silver, which is well known to be affected by rays distributed over a larger portion of 
* Since the paper was read the frequent use of the apparatus has suggested various modifications and im- 
provements, both in its construction and practical application ; these will be inserted in the form of notes for 
the sake of preserving the integrity of the original papers, and at the same time presenting all existing infor- 
mation on the subject. 
The lamps now in use have been constructed by Watkins and Hill, having a detached slit with a fine 
adjustment (see fig. 7, Plate V.) : much nicety is requisite in their arrangement, to enable the camphine to bum 
without smoking, at a point nearly approaching the maximum of illumination. 
If the lamp and slit by which the base-line is described be similarly fixed in position, and the angular value 
of the distance between the base-line and the register at any given time determined, the declinations may be 
read off from the registers, with a limit of error depending on the length of scale and the definition of the line. 
—May 1847. 
