HISTORY OF DEEP-SEA SOUNDINGS 17 



who first introduced the use of isobathic curves in a 

 map which he published in 1737. His view, that the 

 depths of the ocean are simply prolongations of the 

 conditions existing in the neighbouring sea -coasts, 

 though too wide in its generalization, has been shown 

 to be true as regards the sea-bottom in the immediate 

 vicinity of Continental coasts and islands ; and un- 

 doubtedly it helped to attract attention to the problem 

 of what is taking place at the bottom of the sea. 



Actual experiment, however, advanced but slowly. 

 So early as the fifteenth century, an ingenious Cardinal, 

 one Nicolaus Cusanus (1401-1464), had devised an 

 apparatus consisting of two bodies, one heavier and 

 one lighter than water, which were so connected that 

 when the heavier touched the bottom the lighter was 

 released. By calculating the time which the latter 

 took in ascending, attempts were made to arrive at 

 the depths of the sea. A century later Puehler made 

 similar experiments ; and after another interval of a 

 hundred years, in 1667 we find the Englishman 

 Robert Hooke continuing on the same lines various 

 bathymetric observations ; but the results thus obtained 

 were fallacious, and the experiments added little or 

 nothing to our knowledge of the nature of the bottom 

 of the ocean. In the eighteenth century Count Mar- 

 sigli attacked many of the problems of the deep sea. 

 He collected and sifted information which he derived 

 from the coral -fishers; he investigated the deposits 

 brought up from below, and was one of the earliest 

 to test the temperature of the sea at different depths. 

 In 1749 Captain EUis found that a thermometer, 

 lowered on separate occasions to depths of 650 fathoms 

 and 891 fathoms respectively, recorded, on reaching 

 the surface, the same temperature — namely, 53°. His 

 thermometer was lowered in a bucket ingeniously de- 

 vised so as to open as it descended and close as it was 

 drawn up. The mechanism of this instrument was 



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