76 MR. BROOKE ON THE AUTOMATIC REGISTRATION OF MAGNETOMETERS, 
PLATE VIII. 
Fig. 1. Register of April 15 d 4 h to 12 h , another great disturbance. The Greenwich 
observations made during the principal part of the disturbance agree well 
with the register. Scale 20' to 1 inch. 
Figs. 2, 3. The greater part of the term-day, August 28 d 10 h to 29 d 10 h , on the scale 
of 10' to 1 inch. These registers show a general agreement with the 
Greenwich observations ; but it appears that the excursions of the regis- 
tered magnet have been generally less than those of the Greenwich magnet. 
No. 3 shows a constant succession of small disturbances. 
Fig. 4. A register of the thermometer and barometer combined, the two instruments 
being placed on opposite sides of the cylinder. The base-line drawn by 
the barometer lamp may be distinguished through the paler tint produced 
by the light passing through the empty portion of the thermometer tube. 
PLATE IX. 
Fig. 1. Register of August 20 d , showing an unusual absence of disturbance: this is 
not however a solitary instance. 
Fig. 2. Register of September 5 d 0 h to 1 l h 30 m , the greatest magnetic storm of the 
year 1846. It may be remarked, that the excursions of the registered 
magnet, though agreeing in direction, were considerably greater in extent 
than those of the Greenwich magnet. The contrary took place in figs. 2, 3, 
Plate III. This and the preceding are on the scale of 20' to 1 inch. 
Fig. 3. Portion of a register on another piece of the same sheet of paper as the pre- 
ceding, but on the scale of 10' to 1 inch ; to show, cceteris paribus, the re- 
lative intensity of the actinic rays. 
Fig. 4. Register of September 5 d 12 h to 23 h , showing the gradual subsidence of the 
storm. Scale 20' to 1 inch. 
Fig. 5. Portion of the succeeding register of September 6 d 0 h to ll h , on part of the 
same sheet as 4. Scale 10' to 1 inch. The line is equally well-defined, 
but fainter. 
Fig. 6. Register of a term-day, September 23 d 10 h to 22 h , with a photographic base- 
line ; on which the Greenwich observations were laid down at the Royal 
Observatory. This register well illustrates a fact that has been frequently 
noticed, namely, the gradual subsidence of slow excursions into small and 
brief disturbances. The scale is 15' to 1 inch. 
Fig. 7. Another of the great disturbances of 1846; November 17 d 0 h to 12 h with 
base-line, and register of barometric variations magnified five times. The 
nearly horizontal portion of the line between 6 h 20 m , and 30 m , indicates 
the most rapid movement of the magnet that has been recorded by photo- 
graphy. No point of it could have been illuminated more than 16 s . The 
