is'J 



No. 9. — Reports of the Results of Dredging, under the Supervision of 

 Alexander Agassiz, on the East Coast of the United States, hy 

 the U. S. Coast Survey Steamer " Blake,'' Commander J. E. Bart- 

 LETT, U. s. jsr. 



VII. 



Description of a Gravitating Trap for obtaining Specimens of Animal Life 

 from Intermedial Ocean-Depths. By Lieut.-Commander C. D. Sigsbee, 

 U. S N. 



The old practice of dragging for animal forms at intermedial depths 

 by means of a tow-net, which, dm-ing the several operations of lowering, 

 dragging, and hauling back remained open, was not regarded by Pro- 

 fessor Alexander Agassiz as affording acceptable evidence of the habitat 

 of such specimens as were obtained, and he frequently referred to the 

 subject during our association on board the " Blake" in 1878. 



In March, 1880, it having been arranged that Professor Agassiz should 

 make another cruise on board the " Blake," Commander J. R. Bartlett, 

 U. S. N., commanding, he asked my co-operation in devising an apparatus 

 to meet the rigid demands of the work in question. This resulted in 

 the apparatus described herein, which is presented in the precise form 

 used with success by the " Blake," although, as may readily be seen, it 

 is open to great improvement, especially in minor details. 



The " Challenger " had examined intermediate depths by means of tow- 

 nets trailing from the dredge-rope while hauling the dredge or trawl. 

 In such a practice it must have been that the depths to which the nets 

 were sunk depended in some degree on the amount of slack rope payed 

 out, and also on the strain upon the dredge-rope due to the resistance en- 

 countered by the dredge when dragging ; it cannot therefore be said that 

 strictly determinate depths were examined by that method, even assum- 

 ing that the nets gathered nothing while being lowered and hauled back. 



It occurred to me that by using an apparatus in connection with a 

 line and lead, payed out vertically as in sounding, and by dragging ver- 

 tically, instead of horizontally as formerly, there would be at least as 

 much certainty with regard to depths as in the old method, and that 

 simple mechanical devices could be invented to satisfy the conditions of 



VOL. VI. — NO. 9. 



