74 MR. BROOKE ON THE AUTOMATIC REGISTRATION OF MAGNETOMETERS, 
extremity of the hour-hand, that engages with the carrier on the axis of the 
cylinder. 
Fig. 4. A sketch of the apparatus for carrying a vertical cylinder, with the requisite 
arrangement of lenses for combining the registers of the balanced mag- 
netometer and barometer, or of the thermometer and psychrometer. 
Fig. 5. A vertical cylinder, with its outer cylinder. A hole in the centre of the cap 
fits over a pin in the centre of the plate on which it rests, and is carried 
round. 
Fig. 6. The horizontal plate on which the cylinder rests. The under surface of this 
plate rests on the edges of three equidistant vertical friction wheels or rollers, 
attached to the frame beneath it. A vertical pin fixed to the centre of the 
under surface of the plate passes down between the edges of three equi- 
distant horizontal rollers, which are attached to the under surface of the 
frame, and on this pin the carrier is fixed. 
Fig. 7- A frame supported on three legs, to which the friction rollers above described 
are attached. By this arrangement the motion is so easy that the effect of 
the drag on the rate of the time-piece is scarcely sensible. 
Fig. 8. The time-piece, the rim of which is let into the surface of the stand. In doing 
this great care should be taken that the axis of motion of the hour-hand is 
continuous with the axis of the cylinders, and of the plate on which they 
rest. In registering the balanced magnetometer, as in the declinometer, 
the cylinder makes two revolutions in 24 h , and two 12 u lines are traced on 
the paper ; but for the thermometers, the cylinder, and consequently the 
hour-hand makes only half a revolution in 24 h , and each of the two ther- 
mometers is registered on one-half the paper during that time. The cylin- 
der is about 19 inches in circumference, which suits the length of a sheet 
of folio post writing-paper. 
Fig. 9. An elevation of the bifilar carrier. 
Fig. 10. A side view of the same. The centres of gravity of the carrier, the mirror, 
and the magnet, are very nearly in the same vertical line. 
Fig. 11. An elevation of the thermometer tube. 
PLATE VII. 
Figs. 1, 2. Show the increased sensibility of the paper by the addition of a very small 
quantity of the iodide of potassium to the first solution. 
Fig. 3. Shows the effect produced upon the line by the want of horizontal adjust- 
ment of the plane of incidence and reflexion, compared with 
Fig. 4, in which this adjustment has been carefully made, all other circumstances 
remaining the same. 
Fig. 5. Specimen of a well-defined line, on the scale of 10' to 1 inch. 
