478 Pierre H. Willm 
if the electrochute is blocked. In any case, the ballast is automatically released in the 
event of a power failure. 
External pressure acts freely on the petrol through a stabilizing hole, in the bottom of 
the float. Unfortunately, this petrol has an important drawback: it is very compressible. 
When the bathyscaph sinks, the petrol is compressed and sea water enters the float. 
The resulting increase in weight is markedly greater than the apparent decrease in 
weight due only to the increasing density of sea water. Therefore, once the bathyscaph has 
started to sink, it descends quicker and quicker. It is necessary to discharge shot during 
the descent, in order to slow down this movement and to avoid sinking into the soft muddy 
bottom from which it would perhaps be difficult to break loose. On the other hand, once the 
bathyscaph starts going up, its speed increases progressively and it is impossible to stop 
it. The maximum speed under such conditions is approximately 1 metre per second. 
Sphere and float are joined by a metal frame. The float is surmounted by a narrow deck 
running from stem to stern, with a conning tower in the center, in order to protect from heavy 
seas, during the towing of the bathyscaph to the diving site, the various external fittings 
that have to be placed there and the upper hatch of the entry shaft to the sphere. This 
entry shaft runs vertically through the float and enables passengers to enter or leave the 
sphere while the bathyscaph is afloat. It also acts as the submersible’s water-ballast; that 
is to say, being normally empty on the surface, it fills with water during diving. The 
increase in weight when it is flooded with water is enough to make the machine submerge. 
Added to this, there are also devices enabling one to tow the bathyscaph on the surface, 
to fill the entry shaft (by a flooding valve in the bottom) and to empty it (by means of com- 
pressed air), to land on the bottom with the aid of a guide chain, and to drive it horizontally 
while under water. There is exterior lighting, for detection of the sea floor and of obstacles 
ahead, and means of communication with the outside world while under water or on the sur- 
face, various measuring instruments, and so on. I shall give a fuller description of these 
accessories in the next section concerning the FNRS-3. 
THE BATHYSCAPH FNRS-3 
The sphere of the FNRS-3 is made of cast steel containing nickel, chromium, and 
molybdenum, with a yield point of 95 kg/mm? after heat treatment. It was built by the 
Emile Henricot steel works, at Court St Etienne, in Belgium. Its inside diameter is 2 
metres, and its thickness 9 centimetres, reinforced to 15 centimetres around the hatch and 
porthole. It is composed of two hemispheres separated by the equatorial plane normal to 
the porthole-hatch axis. The joint consists of the two metal faces bearing one upon the 
other. The hemispherical parts are held together, with an initial force of 24 tons, by 400 
steel clamps gripping two flanges machined on both sides of the joint. 
Water tightness at low depth is ensured by a synthetic rubber ring which is fitted on 
the sphere before setting up the clamps. The viewing portholes, made of Plexiglas, 150 
millimetres thick, are shaped in a frustum of a cone, with two parallel planes and forming 
an angle of 90 degrees at the apex. The internal and external planes have a diameter of 
100 and 400 millimetres, respectively. At great depths, the watertightness of the joint 
between porthole and sphere is ensured by the plasticity of the Plexiglas. The hatch is 
made up of a steel frustum of a cone with two parallel planes and an angle of 45 degrees at 
the apex. At the center, it has a porthole which is similar to the viewing port. This hatch, 
weighing about 140 kilograms, is hinged about an axis and balanced in all positions, like a 
