Joty— Geological Investigation of Submarine Rocks. 513 
on strong vertical spindles, contained in vertical slots carried 
up in the walls of the drill for a few inches. Above, the 
spindles carry each a semi-cylindrical fan which may fold 
down upon the drill-shaft, or swing outwards so as to extend as 
vanes from either side of the drill-shaft, as seen in the plan of 
the drill-saws. These vanes are not rigidly attached to the saw- 
spindles, but only engage upon them when opened into such a 
position as shown in the full lines on the plan. Any further 
opening of the vanes must be accompanied by corresponding 
angular rotation of the saw-spindles. Finally, after a certain 
range of rotation, the vanes are hindered from further deflection 
by stops affixed upon them at the back, which then bear against 
the wall of the drill-shaft. These details of construction are 
omitted. 
Looking at the sectional elevation, it is seen that the vanes, 
when the drill-shaft is in its lowest position, just escape the base- 
plate above them. When the drill occupies a higher position, 
the vanes are, in fact, folded down upon the drill-shaft, and con- 
tained within the hollow armature of the motor. They are sprung 
a little upon their seats, so that upon the descent of the whirling 
drill to its lowest position, as in the drawing, the vanes are released, 
spring out a little, immediately catch the water, and are then 
pressed open till they engage upon the saw-spindles. After this, 
they can only open wider by rotating these spindles, and, in doing 
so, urge the cutting edges of the saws inwards upon the column of 
rock still left standing within the drill. The high rate of rotation 
of the drill ensures that the pressure so brought to bear upon the 
cutting edges of the saws is very considerable, and it is steadily 
maintained till the vanes attain their extreme deflection under the 
pressure of the water. In this position, the saws have met within 
the rock, and occupy the dotted position of the plan. The space 
occupied by the rotating vanes is shut in below by a removable 
perforated plate, and a bodily swirling of the water is checked by 
fixed vanes projecting from the sides. 
When this horizontal cut is finally effected, the measuring 
instruments in circuit at once reveal the fact to those above. ‘lhe 
motor runs away, and the counter e.m.f. generated indicates on 
the voltmeter that the apparatus may be raised. An approxi- 
