590 FISHERIES OF THE UNITED STATES. [7S] 



Belknap cylinder No. 2 being shown in a foot-note on page 44. In that 

 discussion the following are named as amongst the requirements of a 

 perfect sounding rod for work with wire: 



1. Certainty of not detaching the sinker during the descent. 



2. Certainty of detachiDg on striking any character of bottom. 



3. Certainty of not rebooking or of fouling with the sinker in any way 

 after the same has once been tripped. 



4. Adaptability to getting a specimen from the various kinds of bot- 

 tom material. 



5. Certainty of not grappling irretrievably with the bottom. 



6. Certainty of retaining the specimen against the wash of water in 

 the ascent. 



7. Handiness for extracting the specimen and for cleaning the parts 

 of the rod. 



8. Freedom from changing its form under the severe pressure in deep 

 water. 



9. Strength, simplicity, cheapness, lightweight, and freedom from 

 corrosion. 



In the Sigsbee-Belknap rod it has been attempted to cover these points. 

 While the rod might be made lighter, its great strength serves a good 

 purpose on hard rock. In his efforts to obtain a good form of sounding 

 rod — one that would require but little watchful care in its operation — 

 Commander Sigsbee, after much practice and experimeut, decided to 

 modify Captain Belknap's cylinder No. 2, and to apply his own detacher 

 to this modification. The results with this rod have been most grati- 

 fying after more extended use than has probably ever been given to any 

 other rod in sounding with wire. Commander Bartlett was the first to use 

 it, in 1878-'79 ; on his first cruise he used it 250 times, and in no instance 

 did it fail. Since that it has been used in hundreds of casts, and no 

 complaints have been made of its operation. With the rod itself, and 

 detailed drawings on exhibition, no special description of the rod is 

 deemed necessary in this catalogue. 



APPARATUS FOE PHYSICAL OBSERVATIONS, &C. 



The Bailie-Tanner Thermometer Attachments, for serial and deep-sea tem- 

 peratures, with the Negretti and Zambra deep-sea thermometers. 



United States Fish Commission. 



Case for use with a messenger. — The Negretti and Zambra deep-sea 

 thermometers, which register by tripping, were adopted for use by the 

 United States Fish Commission in 1878, and have been employed since 

 then in all the explorations of that survey. During the first two years, 

 the wooden case with shifting weight furnished by the makers was the 

 only one used, but it frequently proved unreliable, especially when the 

 vessel was rolling much. In 1880, Lieutenant Tanner, United States 



