a slight manipulation of the hinge overcame this difficulty. The 

 resistance that the door offers to manipulation is nil in an open position. 

 It reaches its maximum when closed and this maximum is one-third 

 of the maximum which would be required for a door with a horizontal 

 axis (sine 1 8°= 0-30902). Even reduced to one-third, this resistance 

 would still be too great to allow the door to be opened with one hand. 

 That is why we also placed a torsion-spring around the hinge. The 

 principle of this spring is explained in the Appendix and, in fact, 

 permits the door to be opened and shut very easily with one hand. 



A rubber ring which is pressed automatically against the joint of the 

 door, as soon as it is closed, ensures watertightness. 



So that the door may remain well closed, even if the external 

 pressure of the water is slight, a small screw placed opposite the hinge 

 keeps it in position. 



This method of closing gave us complete satisfaction. It allowed 

 very rapid opening and closing and did not require the great effort 

 which was necessary to close the door of the FNRS 3. Moreover one 

 could, to go through the manhole, use the entire width of the opening, 

 of which the diameter was 16-9 in., whilst in the cabin of the FNRS 2 

 and the FNRS 3 it was generally necessary to leave in place the closing 

 ring, which is only 14-56 in. in internal diameter and which, for 

 certain people, made getting in and out much more difficult. 



After the dive it can happen that the door adheres to the greasy 

 walls. It was easily unstuck by means of another little screw placed 

 beside the first one. 



JOINING THE HEMISPHERES 



Fig. 10 shows how the two hemispheres a and b are joined together. 

 To the edge of each of them is joined a sort of flange : the two flanges 

 are clamped together by means of two rings g and h which are them- 

 selves riveted and welded to each other. The exact centring is ensured 

 by a circular pin /which enters into two grooves machined into the 

 flanges. A rubber band c thermally insulated by a layer of asbestos d , 

 placed over the joint and stretched lightly around the two hemispheres, 

 functioning as an autoclave, ensures a perfect seal.^ As a precaution, 



1 From many points of view it would have been simpler to give enough 

 breadth to the flanges to allow them to be fixed directly by bolts and rivets. 

 However, for reasons of manufacture we gave up this solution which, as well, 

 would have necessitated an accumulation of material prejudicial to uniform 

 distribution of the stresses. 



[89] 



