74 INTRODUCTION. 



nature, would perhaps be advantageous ; perhaps 

 a brass wire might be used for the purpose, such as 

 is employed in some places, as at TenerifFe, for 

 instance, in fishing. A more convenient contriv- 

 ance for drawing up the line, such as a kind of 

 windlass of considerable diameter, might contri- 

 bute to facilitate this very interesting experiment. 



To remedy this and other difficulties, in measur- 

 ing the depth of the sea, instruments have long 

 since been contrived, which are known by the 

 name of bathometers. Most of these are, at the 

 bottom, no more than repetitions of the proposal of 

 Dr. Hooke, which chiefly consists in the following 

 contrivance. To a long pole of liglit wood, a 

 heavy w^eight, for instance a cannon ball, is fast- 

 ened in such a manner, that, in sinking, it carries the 

 pole with it ; but when it strikes the bottom, re- 

 leases the pole by the knocking out of a hook ; so 

 that the pole rises to the surface by its specific 

 lightness. At, first it was attempted to deduce 

 from the time the pole remained under water, the 

 depth which it had reached, but as this implied 

 difficult experiments, and the moment M^hen the 

 pole re-appeared might be easily missed, it was 

 afterwards found better to fasten to it a kind of 

 hodometer (or way-measurer,) such as had been 

 proposed, instead of the common logs, the wheel- 

 work of which was immediately stopped on taking 

 it off. To this, in itself, ingenious idea, nothing is 

 to be objected, but the difficulty of immediately 



