240 



On a New Deep-sea Thermometer. 



[Mar. 



sa y s : "With a view to obviate this failing, Messrs. Negretti and Zambra 

 undertook to make a case for the weak bulbs, which should transmit 

 temperature, but resist pressure. Accordingly a tube of thick glass is 

 sealed outside the delicate bulb, between which and the casing is a space 

 all round, which is nearly filled with mercury. The small space not so 

 filled is a vacuum, into which the mercury can be expanded, or forced by 

 heat or mechanical compression, without doing injury to 

 or even compressing the inner or much more delicate 

 bulb." 



The thermometers now in use in the ' Challenger' Expe- 

 dition are on this principle, the only difference being that 

 the protecting chamber has been partly filled with alcohol 

 instead of with mercury ; but that has nothing to do with 

 the principle of the invention. 



We have therefore a protected bulb thermometer, like 

 a siphon with parallel legs, all in one piece, and having a 

 continuous communication, as in the annexed figure. The 

 scale of this thermometer is pivoted on a centre, and 

 being attached in a perpendicular position to a simple 

 apparatus (which will be presently described), is lowered 

 to any depth that may be desired. In its descent the 

 thermometer acts as an ordinary instrument, the mercury 

 rising or falling according to the temperature of the stratum 

 through which it passes ; but so soon as the descent 

 ceases, and a reverse motion is given to the line, so as to 

 pull the thermometer to the surface, the instrument turns 

 once on its centre, first bulb uppermost, and afterwards 

 bulb downwards. This causes the mercury, which was 

 in the left-hand column, first to pass into the dilated si- 

 phon bend at the top, and thence into the right-hand tube, 

 where it remains, indicating on a graduated scale the ex- 

 act temperature at the time it was turned over. The wood- 

 cut 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 com- 

 pressed ; D is a small glass plug on the principle of our 

 Patent Maximum Thermometer, which cuts off, in the 

 moment of turning, the mercury in the column from 

 that of the bulb in the tube, thereby ensuring that none 

 but the mercury in the tube can be transferred 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 



