[71J U. S. FISH COMMISSION STEAMER ALBATROSS. 73 



and the shield effectually preserves them from obliteration. The part 

 of the .stem which foruis the background to the graduations is enameled 

 v.hite to give distinctness to the mercury. 



To make this instrument available for deep-sea use it is necessary to 

 provide some reliable method of turuing the bulb upward at the proper 

 time; also, to prevent it from turning down again before the surface is 

 reached and the tejnperature read. 



Plate XXXVIII shows a metal frame devised by Commander Mag- 

 naghi of the Italian navy. It is described as follows in an advertise- 

 ment of Messrs. Negretti & Zambra: 



NEGRETTI & ZAMBRA'S PATENT IMPROVED FRAME STANDARD DEEP- 

 SEA THERMOMETER. 



"Thj apparatus will be best understood, short of inspection, by refer- 

 ence to Plate XXXYIII, Figs. I and 2. A is a metallic frame in which 

 the case B containing the thermometer is pivoted upon an axis H, but 

 not balanced upon it. is a screw-fan attached to a spindle, one end 

 of wliicli works in a socket D, and on the other end is formed the thread 

 of a screw E, about half an inch long, and just above it is a small ])in 

 or stop, F, on the spindle. G is a sliding top-piece against which the 

 pin F impinges when the thermometer is adjusted for use. The screw 

 E works into the end of the case B, the length of play to which it is 

 adjusted. The number of turns of the screw into the case is regulated 

 by means of the pin and stop-piece. The thermometer in its case is 

 held in position by the screw E and descends into the sea in this 

 position (Fig. 1), the fan C not acting during the descent because it is 

 checked by the stop F. When the ascent commences the fan revolves, 

 raises the screw E, and releases the thermometer which then turns over 

 aftd registers the temperature of that spot, owing to the axis H being 

 below the center of gravity of the case B as adjusted for the descent. 

 Each revolution of the fan represents about 2 feet of movement through 

 the water, so that the whole play of the screw requires 70 or 80 feet 

 ascent; Iherefore, the space through which the thermometer should 

 Ijass before turning over must be regulated at starting. If the instru- 

 ment ascends a few feet by reason of a stoppage of the line while at- 

 taching other thermometers, or through the heave of the sea, or any 

 cause whatever, the subsequent descent will cause the fan to carry 

 back the stop to its initial position, and such stopi)ages may occur any 

 number of times provided the line is not made to ascend through the 

 space necessary to cause the fan to release the thermometer. 



When the hauling in has caused the turn-over of the thermometer 

 the lateral spring K forces the spring L into a slot in the case B and 

 clamps it (Fig. 2) until it is received on board, so that no change of 

 position can occur in the rest of the ascent from any cause. 



The case B is cut open to expose the scale of the thermometer, and 

 is also perforated to allow free entry of the water." 



