98 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [96] 



course, and find the depth,. 1,000 fathoms, in the difference of latitude 

 column (taking one-tenth of the amount), 100.4 being the nearest num- 

 ber. Opposite to this, in the distance column, is 131, which being mul- 

 tiplied by 10 gives 1,310 fathoms, the hypotenuse of the right triangle 

 we have constructed. As the rope has a catenary curve it is necessary 

 to make an allowance in order to insure the trawl reaching and remain- 

 ing on the bottom. Experience has taught us that about 200 fathoms 

 is sufficient with the above depth and angle ; therefore, with a scope of 

 1,500 fathoms, and the angle of the rope maintained between the limits 

 of 35 degrees and 40 degrees, a successful haul may be anticipated as far 

 as the landing and dragging of the trawl on the bottom is concerned. 

 The speed can be easily regulated, after a little practice, so as to confine 

 the rope between the above limits. 



The quadrant is made double in order that it may be used on either 

 side of the vessel, whether steaming ahead or backing. 



SIGSBEE'S GEAVITATIWa TRAP (PLATES LIU, LIV, AND LV). 



The tow net was among the first apparatus used by naturalists to ol) 

 tain minute animal forms from the surface of the sea, and the same ap- 

 paratus has been used for collecting at intermediate depths, various 

 methods being employed for sinking it. The range was confined within 

 narrow limits, generally not exceeding a few fathoms below the surface, 

 and even then it was not altogether satisfactory, as specimens mi^ht be 

 taken while sinking the net, or hauling it up, their habitat still remain- 

 ing a mystery. 



The dredge rope was brought into requisition on the Challenger, the 

 tow net being secured at the point required to sink it to the desired 

 depth, but the same cause for doubt still existed as to the locality in 

 which specimens were caught in the open-mouthed net, which was twice 

 dragged through the intervening space between the surface and the 

 working depth. The same practice was followed on board of the Fish 

 Hawk until we improved upon it by adopting the wing nets, which were 

 secured to the ends of the trawl beam and acted as collectors from the 

 surface to the bottom, along the bottom as far as the trawl was dragged, 

 and again from the bottom to the surface. There was no pretense of 

 locating the habitat of the myriads of specimens taken in this manner, 

 the nets being used for the simple purpose of making the capture. 



The specimens procured by any of the methods above mentioned can- 

 not be assigned to determinate depths. Feeling the need of some de- 

 vice by which this desirable end could be obtained. Prof. Alexander 

 Agassiz, in 1880, requested Lieut.-Oommander C. D. Sigsbee, U. S. Isf., 

 to co-operate with him in devising the necessary apparatus. 



Sigsbee says, with reference to the matter (Bulletin of the Museum of 

 Coniparative Zoology, Cambridge, vol. vi, pp. 155-6) : 



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

 ,Une and lead, paid out vertically as in sounding, and by dragging vei- 



