INTERNATIONAL EXHIBITION AT SOUTH KENSINGTON. 289 
wet portion rejects it. There is, however, this difference in 
the heliotype plate, that it is somewhat of a spongy nature and 
swells, leaving the picture also more or less depressed according 
to the depths of the tints as well as proportionately adhesive to 
ink. The rapidity with which this process can be applied was 
well exemplified in the present instance. The order to take 
the negative was given to the Stereoscopic Company at the 
Exhibition at 8 a.m.; the negative was delivered to a mes- 
senger at 10 o’clock, sent to Willesden Lane, wdiere the Helio- 
type Works are located; two hours were taken up by telegra- 
phic communications, through an accidental omission in for- 
warding instructions for dimensions, the negative having been 
taken on a large glass ; the proof was sent for inspection by 
post, returned, and the printing of the plates for this journal 
was actually commenced at ten o’clock the next morning, 
being regularly continued at hand press until the whole 
required number was completed. Ten thousand impres- 
sions can be printed from a single gelatine plate without 
deterioration, and of course any number of gelatine plates 
for working at any number of presses can be taken from the 
same photographic negative ; and these being done during 
the same period would, of course, produce results almost exactly 
identical. 
Turning to other less familiar applications of inventive skill, 
we may take Admiral Inglefield’s Hydrostatic Steering Hear, 
which has been applied to some of her Majesty’s large iron- 
clad ships with perfect success. To steer such ponderous 
monsters is very far from being easy ; in rough weather from 
twenty to even forty men are required at the tiller, and the 
force of the waves wfill even then sometimes cast the whole of 
them adrift. At the bottom of a deep ship such as these 
there is the great hydrostatic pressure due to the twenty or 
thirty feet of water in which the ship swims. Admiral 
Inglefield uses this as the source of a most powerful inter- 
mittent force. He allows the water to come into cylinders, 
and to work pistons within them much after the manner 
steam would do in an ordinary engine ; and thus he acquires, in 
small hydraulic rams attached to the tiller, a motive power 
equal to 1,000 lbs. to the inch of surface. A single man now, 
by this method, can steer the largest ship in the wildest 
weather. This example typifies admirably the class of inven- 
tions brought to a practical application. 
In Mr. Tommasi’s model for utilising the tides as a source of 
power for machinery, we have an idea not yet practically realised, 
and typical of another class — unrealised inventions. Men long 
ago have looked to this solemn source of enormous but totally 
