512 Scientific Proceedings, Royal Dublin Society. 
amount of work is being done. The readings of the voltmeter 
are, in fact, those we observed when we ran the drill in shallow 
water with the cutting edge unemployed. Finding this, we raise the 
-apparatus a little, and shift our ground, and so make trials. till 
we find that the drill becomes engaged after we lower the drill 
but a little way. The readings in this case change character. 
The voltage and current now not only tell us that the drill is 
at work, but we may ‘tell immediately at what rate it is doing 
work. The presence of the spiral spring thus confers a pore 
of feeling its way upon the apparatus. 
To guard against the tendency of the whole mathe to turn 
with the drill, considerable mass is conferred, in addition to the 
heavy nature of the machinery, by the presence of a heavy base of 
lead beneath the motor, and sharp claw-like feet. But in con- 
ferring the best form upon these feet, experiment will probably be 
needed, in the case of the coral reef, standing at a high slope, a 
much wider base would be required. 
I may observe here that it is probably unadvisable to seek to 
render any part of the apparatus watertight. The internal space 
around the motor may, if desired, be filled with a thin oil, such 
as paraffin, before submergence. 
It will be perceived that, in the diagram, the drill is depicted 
in its lowest position ; the ring carrying the fan-blades has come 
‘into meeting with the collar encircling the spiral spring. It 
-would save loss due to friction if this collar, which stops the down- 
ward descent of the drill, was a prolongation of the tubular shaft 
containing the drill, and hence turning with it. Similarly the 
spring might well rotate with the outer shaft. In this design, the 
vertical range of the drill is only something about an inch. It 
is intended for both hard and soft rocks. A greater range would 
be desirable in the case of the coral reef. In the diagram, the 
vertical cut is supposed to be completed. The drill has attained 
‘the lowest point in its vertical range. 
The mechanism by which the dissevering of the bored-out 
plug is effected remains to be described. Near the lower extremity 
of the drill, just above the cutting edges, two horizontal slots 
are carried through the thickness of the metal. ‘These house 
two curved saws, armed with diamonds, These are pivoted 
