AND OTHER METEOROLOGICAL INSTRUMENTS, BY PHOTOGRAPHY. 75 
Fig. 6. The development of a recent impression, and the decay of another made 
twelve hours previously, and very near the former. 
Figs. 7 , 8. The comparative effects of the camphine and oil lamps, they having been 
exchanged for the purpose of experiment. 
Fig. 9. The commencement of the magnetic storm of September 5th, 1846. The oil 
lamp was in use, and this shows its inability to impress the photographic 
paper during rapid movements of the magnet, when the registration is 
most important. 
Fig. 10. The greatest magnetic shock that has been observed during the year*. It 
occurred on April l d 5 l1 20 m . 
Figs. 11, 12, 14. Examples of shocks, of these No. 12 is the least impulsive. It may 
be remarked, that in these and in all other recorded shocks, the first im- 
pulse has been to the west, and has been followed shortly after by a second 
to the east. 
Fig. 13. Tremor continuing for more than an hour. This occurred on April 25 d , 
between 20 h and 22 h , and from the habitual quietude of the streets at such 
a time, cannot probably be attributed to local causes. 
Fig. 15. A register of July 12 d 3 h to 8 h , showing an unusually frequent repetition of 
small oscillations. These oscillations, which have been frequently noticed, 
differ considerably from the shocks ; the magnet appears to be disturbed 
from a state of rest by gradually increasing oscillations, which, after having 
attained a maximum, subside in nearly an equal time : the period of these 
disturbances is from two or three to ten or fifteen minutes. 
Fig. 16. The effect of a maximum local disturbance — a quadrille party in the adjoin- 
ing house. The unsteady movement of the magnet is well-contrasted with 
the preceding disturbances. 
Fig. 17. A disturbance which occurred on April 15 d 8 h to 9 h . This differs more 
essentially from the Greenwich observations than any that has been com- 
pared: in the curve laid down by points from the observations made at the 
Royal Observatory, two sharp cusps correspond in time to mere undula- 
tions in the register. May it not be inferred that in this instance the 
disturbing cause was sensibly nearer to Greenwich than to Keppel Street ? 
Fig. 18. The register of August l d 2 h to 1 l h , during which period the great hail-storm 
occurred. 
Fig. 19. A register obtained at the Royal Observatory, without a damper. The 
oscillations of the magnet gradually diminished, and after 6 h 40 m it returned 
to a state of rest. 
Fig. 20. The register of April 6 d l h to 13 h , one of the great disturbances of the year 
1846. A very close agreement may be observed between the register and 
the Greenwich extraordinary observations, made between 8 h and 10 b . In 
all the figures of this Plate, except fig. 5, the scale is that of 20' to 1 inch. 
* All the dates except that of fig. 8, Plate IX. refer to the year 1846. 
L 2 
