52 PROTO-BATHYSPHERES 



about with such Leather bags fas were mentioned beforej 

 to keep out the water. It will not be convenient perhaps 

 that the motion in these voyages should be very swift, be- 

 cause of those observations and discoveries to be made 

 at the bottom of the sea, which in a little space may 

 abundantly recompense the slowness of its progress. 



"If this Ark be so ballast as to be of equal weight with 

 the like magnitude of water, it will then be easily movable 

 in any part of it. 



"As for the ascent of it, this may be easily contrived, 

 if there be some great weight at the bottom of the ship 

 (being part of its ballast) which by some cord within may 

 be loosened from it; As this weight is let lower, so will 

 the ship ascend from it (if need be) to the very surface 

 of the water; and again, as it is pulled close to the ship, 

 so will it descend. 



"For direction of this Ark, the Mariners needle may be 

 useful in respect of the latitude of places; and the course 

 of this ship being more regular than others, by reason it 

 is not subject to Tempests or unequal winds, may more 

 certainly guide them in judging of the longitude of places. 



"3. But the great difficulty of all will be this, how the 

 air may be supplied for respiration: How constant fires 

 may be kept in it for light and the dressing of food; how 

 those vicissitudes of rarefaction and condensation may be 

 maintained. 



"It is observed, that a barrel or cap, whose cavity will 

 contain eight cubical feet of air, will not serve a Diver 



