Messrs. Negretti and Zambra on a Deep-sea Thermometer. 309 



been partly filled with alcohol instead of with mercury ; but that 

 has nothing to do with the principle of the invention. 



We hare therefore a protected bulb thermometer, like a siphon 

 with parallel legs, all in one piece, and having a continuous com- 

 munication, as in the annexed figure. The scale of this thermo- 

 meter is pivoted on a centre, and, beiug attached in a perpendi- 

 cular position to a simple apparatus (which will be presently de- 

 scribed), is lowered to any depth that may be desired. In its 

 descent the thermometer acts as an ordinary instrument, the mer- 

 cury 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 siphon bend at the top, and thence into the right-hand 

 tube, where it remains, indicating on a graduated scale the exact 

 temperature at the time it was turned over. The woodcut 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 cy- 

 linder ; C is the space of rarefied air, which is reduced if the outer 

 casing be compressed ; D is a small glass plug on the principle of 

 our Patent Maximum Thermometer, which cuts off, in the mo- 

 ment 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 E is the indi- 

 cating 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 even- 

 tually falls into the tube E, when this tube resumes its original 

 perpendicular position. 



The contrivance for turning the thermometer over may be de- 

 scribed as a short length of wood or metal having attached to it a 

 small rudder or fan ; this fan is placed on a pivot in connexion 

 with a second, and on this second pivot is fixed the thermometer. 

 The fan or rudder points upwards in its descent through the water, 

 and necessarily reverses its position in ascending. This simple 

 motion or half turn of the rudder gives a whole turn to the ther- 

 mometer, and has been found very effective. 



Various other methods may be used for turning the thermo- 

 meter, such as a simple pulley with a weight which might be released 

 on touching the bottom, or a small vertical propeller which would 

 revolve in passing through the water. 



