592 FISHERIES OF THE UNITED STATES. [80] 



previously placed upon the sounding wire, and hangs suspended from a 

 hook attached to the guiding pulley of the sounding machine. The ther- 

 mometer is now lowered in the ordinary way, and after it has been 

 down a sufficient length of time the messenger is dispatched with a quick 

 throw. No failure to trip the thermometer by this means has been noted 

 since the introduction of this style of case. It has been used success- 

 fully and repeatedly down to depths of 700 and 800 fathoms, but in very 

 deep water too much time would be required for the downward passage 

 of the messenger, and for such purposes an automatic attachment i§ 

 substituted for the messenger head. 



The weight of this case is such that, having once tripped, no move- 

 ment of the vessel while rolling can cause it to revert to its original 

 upright position, even for a short interval of time. For taking serial 

 temperatures, as many of these cases as are required may be attached 

 to the same soundiug wire, and arranged at suitable distances apart. 

 The same number of messengers are strung upon the wire, the upper 

 one being suspended from the sounding machine and the remainder in 

 succession from the hook of each thermometer case, excepting the 

 lower. The tripping of the upper case frees the messenger hanging 

 from it, which falls to the second case, and so the action continues 

 to the end of the series. When taking serial temperatures the larger 

 size of sounding wire, (No. 18, American gauge), elsewhere described, 

 is necessary to sustain the extra weight of the several thermometer 

 cases. 



Automatic attachment. — The automatic attachment devised by Mr. 

 Bailie replaces the messenger head on the above-described case, when 

 working in such depths of water that too much valuable time would be 

 lost in the descent of a messenger. It consists of a cylinder 3 inches 

 long by 2 inches across outside, containing a spindle furnished about 

 the middle with three curved propeller blades, each If inches long and 

 three-fourths of an inch broad. The cylinder is fitted above with 

 an open-work screw cap, having a nut in the center ; below it is cut 

 broadly away on two sides, to permit of the free entrance of water, and 

 is joined to a smaller cylinder, about If inches long, which screws onto 

 the tube containing the thermometer. The slip-hooks are hinged to- 

 gether in the center, pass out through a large square slot in the side of 

 the smaller cylinder, and are closed at the. points by being pressed to- 

 gether at their inner ends, the reverse action allowing them to open. 

 The spindle, which extends vertically through the larger cylinder, is 

 furnished with a screw thread above the blades, by means of which it 

 screws up and dowu through the nut in the cap. The lower part of the 

 spindle is 2 inches long and smooth ; for the upper 1£ inches of its 

 length it is over one-fourth of an inch thick, but beyond that it rapidly 

 diminishes in size to a diameter of less than one-eighth of an inch. 

 This termination of the spindle is called the cone end. The entire 

 lower portion of the spindle, below the blades, is free to enter the 

 smaller cylinder through a small hole in the top, providing no obstruc- 



