62 



NEGEETTI AND ZAMBRA, HOLBORN TIADUCT, K C. 



turned over. Fig. 69 shows the 



position of the mercury after the 



instrument has been thus turned on 



its centre. A is the bulb ; B the 



outer coating or protecting cylinder ; 



C is the' space of rarefied air, which 



is reduced if the outer casing be 



compressed ; D is a s mall glass plug 



on the principle of Negretti and 



Zambra's Patent Maximum Ther- 

 mometer, which cuts off, in the 



moment of turning, the mercury in 



the tube from that of the bulb, 



thereby insuring that none but the 



mercury in the tube can be trans- 

 ferred into the indicating column ; 



E is an enlargement made in the 



bend so as to enable the mercury 



to pass quickly from one tube to 



another in revolving ; and F is the 



indicating tube or Thermometer 



proper. In its action, as soon as the 



Thermometer is put in motion, and 



immediately the tube has acquired 



a slightly oblique position, the 



mercury breaks off at the point D, 



runs into the curved and enlarged 



portion E, and eventually falls into the tube F, when this 



tube resumes its original perpendicular position. 



The contrivance for turning the Thermometer over 



may be described as a metal frame with a vertical screw 



propeller; to this frame (fig. 70) the instrument is attached- 



In its descent through the water the screw is lifted out of 



gear and revolves freely on its axis ; but so soon as the 



apparatus is pulled up towards the surface the screw falls 



into gear and revolves in the contrary direction, turning 

 the Thermometer over once, and then becoming locked and immovable, 

 the temperature is recorded for that moment. Price 10 10 



This arrangement of Deep Sea Thermometer (fig. 70) having been found defective, Negretti 

 and Zanibra have abandoned its manufacture it being norc quite superseded by their recently 

 improved Thermometers, particulars of which vill be found in the following pages. Our 

 description is therefore only inserted as a matter of history in connection with the 

 invention of Deep Sea Recording Instruments. 



FIG. 69. 



