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of steam, which in rushing from a boiler under high pressure 
draws all surrounding light bodies into it, and urges them up- 
wards ; the same phenomenon is shown in rapidly flowing water. 
The jet generates rapid currents on every side ; these increase 
the diameter of the moving mass, and it progresses, continually 
increasing in size ; all the currents rushing in towards a moving 
centre, and upwards through that centre as through an inverted 
funnel. The barometer is the truthful indicator of a diminish- 
ing pressure as the centre of the storm approaches the place of 
observation ; and thus the mariner is, by careful attention to this 
instrument, enabled to determine the exact position in which 
his ship may be placed relative to that centre. 
The importance of a knowledge of the Law of Storms, and 
consequently of the means of escaping from the influence of 
these hurricanes, and of indeed employing them to aid the 
ship’s progress, cannot be overrated. The development of the 
'Law furnishes a fine instance of the value of observation. 
Examples of a similar kind might be quoted in connexion 
with electrical science. Careful observation has dispelled the 
erroneous idea of metals being lightning attractors ; and we 
must be charged with negligence if we allow any elevated 
building to be without its pointed rod, by which the thunder 
cloud may be quietly discharged. The lightning is no more 
attracted by a pointed metal rod than is the rain falling upon 
a housetop attracted by the pipes placed so as to allow the 
water to flow to a lower level ; the rods furnish the channel 
through which the electricity freely flows ; and tower or ship 
may be surely protected if provided with bands or rods of 
copper sufficiently large to carry off the accumulated electricity, 
and to restore the equilibrium of forces. 
The electricity of mineral veins has been a subject of much 
interest; it having been supposed that the currents detected 
were indications of the operations of this agency in producing 
the metalliferous deposit. From my own investigations in the 
principal mines in Cornwall I am disposed to consider these 
electrical currents as due to the chemical decomposition going 
on within the lode itself. It must, however, be admitted that 
the peculiar disposition of dissimilar ores within the same 
B 
