III. SPECIAL THERMOMETERS. 687 



To set this thermometer for a new observation hold the ball downwards in 

 the hand, with a gentle shake the mercury in the tube will unite with that 

 in the ball. 



The minimum is upon Rutherford's principle. A small glass index floats 

 in the spirit ; its end farthest from the ball is flattened. To set the thermometer 

 gently incline it with the ball uppermost, the index will then fall to the end 

 of the film of spirit ; place it in a horizontal position, as the temperature 

 falls the index Avill be drawn back by the last film of spirit by attraction and 

 there remain, the lowest point to which the spirit has receded ; on an increase 

 of temperature the spirit passes the index, it cannot move it. 



2826e. Minimum Thermometer, with flat bulb.- 



Dring and Page. 



Constructed with a view to overcome the great drawback to the use of 

 spirit thermometers, sluggishness. The bulb is made flat, so as to expose as 

 large a surface as possible, while the glass is made as thin as is consistent 

 with a non-barometric action. 



2826f. Symons* Earth Thermometer. A portable ar- 

 rangement for showing temperature at any depth, divested of the 

 risk and difficulty of using the long and awkward thermometers 

 hitherto employed for this purpose. L. Casella. 



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 7a. 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- 

 er 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. 



282 7c. 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 



