688 SEC. 14. METEOROLOGY. 



the clock, and when the hand arrives at the hour determined upon, and to 

 which the clock is set, as in setting an alarum clock, a spring is released, and 

 the thermometer turns over (as in the case of the patent deep sea thermo- 

 meter), transferring the mercury from the thermometer to the auxiliary or 

 recording tube. 



2827d. Board of Trade Thermometer. Original instru- 

 ment, as used formerly in Her Majesty's service. 



Negretti and Zambra. 



The scale is brass, which, after constant use in salt water, soon becomes 

 corroded and the figures obliterated. 



2827e. Board of Trade Thermometers, with porcelain 

 scales as patented by Negretti and Zambra, and now universally 

 adopted. Negretti and Zambra. 



2827f. Negretti and Zambra's Patent Self -register- 

 ing Standard Maximum Thermometer. 



Negretti and Zambra. 



This instrument consists of a tube of mercury fitted on an engraved scale. 

 The tube above the mercury is entirely free from air, and at a point in the 

 bend above the ball is inserted and fixed with the blowpipe a small piece of 

 glass, which acts as a valve, allowing mercury to pass on one side of it when 

 heat is applied ; but not allowing it to return when the thermometer cools. 

 When mercury has been once made to pass the valve (which nothing but 

 heat can effect) and has risen in the tube, the upper end of the column 

 registers the maximum temperature. 



2827g. Negretti and Zambra's Standard Minimum 

 Registering Thermometer, on Rutherford's principle ; an 

 alcohol thermometer for recording the lowest temperature during 

 tiny given period of time. Negretti and Zambra. 



2827h. Negretti and Zambra's Patent Recording and 

 Deep Sea Thermometer. Negretti and Zambra. 



In shape this instrument is like a syphon with parallel legs. At the bottom 

 on the left hand side there is a small glass plug or contraction on the plan of 

 Negretti and Zambra's patent maximum thermometer. The mercury rises or 

 falls as in an ordinary thermometer, but at the moment the temperature is 

 desired to be recorded, the thermometer by a simple contrivance (which may 

 be termed a vertical propeller) is made to pivot on its centre, causing the 

 mercury to break off at the plug, and to pass into the right hand leg, where it 

 remains fixed, indicating the exact temperature. The bulb is protected from 

 the water pressure by an outer covering of thick glass, the intervening space 

 being nearly filled with mercury. 



2827i. Vacuum Solar Radiation Thermometer. 



Negretti and Zambra. 



The instrument consists of Negretti and Zambra's patent maximum ther- 

 mometer with a blackened bulb enclosed in a glass tube and globe from which 

 all air has been exhausted. This form of instrument was first made by 

 Negretti and Zambra. An important addition (patented by Negretti and 

 Zambra) to the instrument has since been made by inserting with the ther- 

 mometer a small mercurial vacuum gauge, thereby showing whether a perfect 

 vacuum has been obtained. 



