APPENDIX. 947 



very small instruments are found to act quite as correctly as the largest, and 

 are much more convenient ; they maybe had with a range sufficient to measure 

 heights of 20,000 feet, with a scale of elevation in feet, as well as of pressure 

 in inches. 



2822. Thermometers. The set of fourteen employed by the 

 Exhibitor in experiments on the sensitiveness of thermometers. 

 (Quarterly Journal Meteor. Soc., Vol. ii, p. 123.) G. J. Symons. 



282 7 a. Plain Thermometer, Thermometer with 

 Enamel Tube. Negretti and Zambra. 



A plain and an enamel thermometer placed side by side, showing the 

 immense advantage of the enamel over the plain. The extremely delicate 

 investigations of medical and scientific men could not be carried on by the aid 

 of such sensitive thermometers as are now manufactured had the process of 

 enamelling not been introduced. 



The enamel tube was invented by Negretti and Zambra. 



282 7b. Negretti and Zambra's Patent Mercurial 

 Minimum Thermometer. Negretti and Zambra. 



This thermometer has a plug of platina wire inserted in a small supple- 

 mentary tube. When the thermometer is inclined, the mercury flows from 

 the end of the supplementary tube until it reaches the platina plug, then by 

 affinity of the mercury for the platina the column is maintained at the existing 

 temperature ; on a decrease of temperature the mercury recedes in the long 

 or indicating tube, but on an increase of temperature it rises in the short 

 tube, leaving the column of mercury in the thermometer indicating the 

 minimum temperature. 



2827c. Negretti and Zambra's Patent Recording 

 Thermometer is upon the same principle as the deep-sea 

 thermometer, but without the protected bulb. 



Negretti and Zambra. 



In this case the instrument is turned over by a simple clock movement, 

 which can be set to any hour it may be desirable ; the thermometer is fixed on 

 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. 



302 



