Jo1y—Geological Investigation of Submarine Rocks. 511 
The armature and field magnets of the motor are indicated 
diagrammatically by the letters A and F. The drill-shaft, it 
will be seen, is continued as a uniform cylinder axially through 
the Feriatuze. In this it is free to move vertically ; but, owing 
to the restraint imposed by projections from the cylindrical shaft 
of the drill engaging in vertical slots in the interior of the arma- 
ture (not shown), is turned with the rotation of this latter. The 
upper extremity of the drill-shaft is furnished with a screw-fan 
which, reacting against the inertia of the water when the drill 
is being rotated, produces the requisite pressure of the latter 
against the rocky bottom. The amount of this pressure is of 
course adjustable, depending upcn the dimensions and pitch of 
the blades of the fan as well as on the rate of speed at which this 
is driven. Experiment must decide the best conditions of velocity 
and pressure for any particular dimension of apparatus. , 
_ When being lowered to the bottom, the spiral spring, shown 
_In section as coiled around the drill-shaft just beneath the fan, 
retains the drill in its highest or most raised position. The fan 
is covered in with a covering of thin sheet-iron, freely perforated, 
or wire-netting, and elsewhere it will be seen that the entire form 
of the apparatus is such as to ensure it against being entangled in 
sea-weeds. 
When the eldch ania of the lowering wire indicates that the 
apparatus has attained the bottom, the current is switched on to 
the motor. An insulated twin-wire connects this with the surface. 
The observer is provided with voltmeter and ampéremeter. 
It is evident that for each voltage read there corresponds a 
particular position of the drill in its vertical path. This is due 
-to the fact that, for slow rates of speed, the fan is working only 
against the reaction of the spring. A few experiments made in 
shallow water will show at what level the driil will stand when 
such-and-such a voltage is indicated. I will suppose now that 
the first lowering of the drill has not been upon a suitable spot ; 
may be it has descended on sand, may be just over a small 
erevice. The observation of the voltage will reveal this at once. 
We find in this case that, as we urge the drill downwards, the 
voltmeter reveals that the armature is still running away without 
meeting any appreciable resistance, or that only an inappreciable 
2P2 
