MAURY'S APPARATUS. 141 



from his description, how it was to be known when 

 the plummet was at the bottom. 



As in all such cases, difficulties and disappoint- 

 ments only stimulated invention. Somebody sug- 

 gested that a quantity of common wrapping twine, 

 marked off into lengths of a hundred fathoms, and 

 rolled on a reel in a definite quantity, would make a 

 good deep-sea line, with a cannon-ball for a plummet. 

 It was thought that as soon as the ball was on the 

 bottom, the reel would stop ; then the twine being 

 cut away, and the remainder measured, the length 

 run off would be known, and the depth obtained at 

 the cost of a cannon-ball and a few pounds of shop- 

 twine. The simple suggestion was presently adopted, 

 and some very deep casts were reported; 34,000, 

 39,000, 46,000 and 50,000 feet of line were run off, 

 but no bottom found, except in the third of these 

 cases, upon which circumstances afterwards threw 

 doubt. It was only now discovered that in great 

 depths the line would never cease to run out of its 

 own accord ; so that there was no means of knowing 

 whether the shot had. reached the bottom. 



These experiments were not, however, lost labour. 

 For by invariably using a ball of the same form and 

 weight, and twine of the same make, it was found 

 that the rate of descent was according to a regularly 

 diminishing scale. This having been well ascertained, 

 it could be determined with approximate accuracy 

 when the shot ceased to carry out the twine, and 



