NARRATIVE OF THE CRUISE. 89 



is to again turn it over slowly, when the mercury in the tube F will fall into the enlarged 

 part E, and from thence into the other tube, rejoining the portion in the bulb, after which 

 it rises or falls in the tube as the temperature increases or decreases. The bulb of the 

 thermometer is protected from pressure by an outer bulb partially filled with mercury. 



" From this description it will be seen that the instrument consists of two parts — the 

 thermometer for recording the temperature, and the machine for rotating the ther- 

 mometer at any required depth. The contrivance for turning the thermometer over 

 may be described as a vertical propeller to which the instrument is pivoted. So 

 long as the instrument is descending the propeller is lifted out of gear and revolves 

 freely ; but as soon as the ascent commences the action of the propeller is reversed, 

 and it falls into gear with a pinion connected with the thermometer, and by these 

 means the thermometer is turned over. After one revolution it becomes locked, and 

 remains immovable. The woodcut (fig. 29 A) shows the general arrangement — T being 

 the thermometer, S a metal screw connected with the frame of the thermometer by a 

 wheel and pinion movement at W ; S + is the stop for arresting the movement of the 

 thermometer when it has made one revolution. It was found in practice that the 

 propeller being arrested, after it had turned over the thermometer, brought such a strain 

 on the cogwheel W as to twist it off the spindle and cause its loss. 



" This defect was remedied by Mr. Ferguson, the Chief Engineer of the Challenger, who 

 applied an ingenious apparatus by which, when the thermometer has made one complete 

 revolution, the pinion is lifted clear of the cogwheel, and thus the propeller is allowed to 

 revolve as freely in its ascent to the surface as it did in its descent. Fig. 29 B shows 

 Mr. Ferguson's improvement. The pinion Z is lengthened considerably, and is connected 

 to the rod L which turns the thermometer by a key on the rod and a slot in the pinion, 

 allowing it to move up and down the rod. M is a brass nut attached to the rod L, and 

 movable up and down that portion of it which has a screw ; from this nut two arms 

 descend, and are attached to a collar round the upper part of the pinion Z. The nut M 

 is kept from revolving by being lengthened sufficiently to clasp one of the supports of the 

 apparatus. As the instrument descends, the wheel W is lifted clear of the pinion as 

 before ; directly it is reversed it falls into gear, but, as the pinion and rod revolve, the 

 nut M is raised on the screw part of the rod lifting with it the pinion, and as long as the 

 rod revolves the pinion is rising ; the length of the pinion is so arranged that when the 

 thermometer has made a complete revolution the lower part of the pinion is just lifted 

 clear of the upper part of the cogwheel, consequently the screw S and cogwheel W can then 

 revolve freely. The apparatus, as thus improved, has been found to answer admirably. 



" Several thermometers for use in the apparatus were forwarded from time to time. 

 A great number were found broken when they reached the ship, owing either to imperfect 

 packing or negligence in the transport, but a sufficient number arrived in safety to 

 admit of their having a fair trial. 



(naer. chall. exp. — vol. i. — 1884.) 12 



