INSULATING WATER-BOTTLE 39 



preciable change within a period of from six to eight 

 minutes, which is amply sufficient for the moderate 

 depths for which it is suitable. At greater depths the 

 readings become inaccurate on account of the pressure, 

 as will be explained below. 



The construction will be understood by reference 

 to the figure. The body of the water-bottle consists 

 of a number of concentric cylinders, of metal and some 

 non-conducting material alternately, and is fitted to 

 slide freely on the two guide bars at the side. These 

 bars are connected at the bottom by a metal plate 

 fitted with a tap and a number of rubber washers. 

 A similar plate is arranged to slide on the guide bars 

 above the body of the water-bottle, and instead of a 

 tap it is provided with a small air valve and a central 

 hole, through which the bulb and the lower part of the 

 stem of the thermometer pass ; they are secured by a 

 gland and rubber washer. A thermometer guard, in 

 the shape of a slotted tube, is fixed to the upper side 

 of this lid and carries two hooked arms at its upper 

 end. To set the water-bottle for use, the lid is raised 

 and the hooks at the top of the thermometer guard 

 are made to engage with the lower part of the spindle 

 of the releasing gear. The striker plate is then raised 

 and the lid is fixed. The body of the water-bottle is 

 next raised until the lugs, which project on each side 

 from its upper rim, engage with the two swinging arms 

 shown pivoted to the lid, and the two small locking 

 levers at the end of the arms are folded upwards, until 

 they pass a spring catch which holds them in position. 

 The lid, body, and bottom plate are now held apart 

 from one another so that the water can pass through 

 freely. The taps and air valves are then closed, and 

 the water-bottle is lowered to the desired depth by 

 means of a steel cord passing through the striker plate. 



