94 



THE VOYAGE OF H.M.S. CHALLENGER. 



Magnaghi, Hydrographer to the Royal Italian Navy, by means of which the thermometer 

 may be attached to any part of the line during the descent ; and after the first regular 

 haul in of from 10 to 80 feet, according to adjustment, any number of stoppages or any 



amount of line may be afterwards run out without 

 altering the temperature obtained at the commence- 

 ment of hauling up. 



The apparatus will be best understood by 

 reference to fig. 31. A is a metallic frame in 

 which the case B, containing the thermometer, 

 is pivoted upon an axis H, but not balanced upon 

 it. C is a screw-fan attached to a spindle, one 

 end of which 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 

 pin or stop F on the spindle. G is a sliding stop- 

 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 being 

 adjusted as necessary. 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 the position shown in the left hand figure, 

 the fan C not acting during the descent because it 

 is checked by the stop F. When ascent commences 

 the fan revolves, raises the screw E, and releases the 

 thermometer, which then turns over and registers 

 the temperature at that spot, owing to the axis H 

 being below the centre of gravity of the case B as adjusted for the descent. Each 

 revolution of the fan represents about 10 feet of movement through the water upwards, so 

 that the whole play of the screw requires 70 or 80 feet of ascent; therefore the space through 

 which the thermometer should pass before turning over must be regulated at starting. 

 If the instrument ascends a few feet by reason of a stoppage of the line while attaching 

 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 stoppages 

 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 thermometer to turn over, the lateral spring K forces the pin L into a slot 

 in the case B and clamps it (as seen in the right hand figure) until it is received on 



Fig. 31. — llagnaghi's reversing apparatus for 

 Negretti & Zambra's Thermometer. 



