686 SEC. 14. METEOROLOGY. 



movable scale of inches, by means of its rack motion, to the corresponding 

 degrees of temperature of the syphon tube, the position of the fluid indicates 

 the height of the barometer. This instrument is considered by many a most 

 valuable instrument ; it is more sensitive than the barometer, and when 

 accurately constructed should give good results. 



III. SPECIAL THERMOMETERS. 



2823. Old Floating Thermometer, by Gay Lussac and 

 Collardeau, of Paris. G. J. Symons. 



2324. Thermometer of Translation or Integrator of varia- 

 tions of temperature. Scottish Meteorological Society. 

 The bar of zinc is fixed at its lower end during expansion by the needle 

 points catching in the teeth of the rack below, so as to produce lengthening 

 upwards, while during contraction the bar is held by the needle at the top, so 

 that the shrinking is upwards. In this way the centre of gravity is moved 

 upwards. The total annual march or creep of the bar will measure the total 

 . amount of fluctuation of temperature. Designed by Thomas Stevenson, C.E., 

 Honorary Secretary. 



2825. Von Lament's Terrestrial Thermometer, for deter- 

 mining the temperature of soil from one to four feet deep. 



Prof. Ebermayer, Aschaffenbury. 



2826. Three Vacuum Thermometers for studying solar 

 radiation. 



2826a. Six's Self-registering Thermometer, for regis- 

 tering the degree of heat and cold. Francis Pastorelli. 



The thermometer is continuous ; in form it appears as three parallel limbs, 

 the interior of the central and shorter one is filled with a fluid, the other two 

 limbs partly with the same fluid and mercury. Floating in the fluid in each 

 of the outside limbs above the mercury are two registering indices ; they con- 

 sist of pieces of fine steel enclosed in delicate glass tubes. Attached to them 

 are hair springs, which retain them in a fixed position, unless acted upon by a 

 force. The force used to set them is a magnet. 



2826c. Standard Maximum Thermometer with divisions 

 on the tube, protected by a glass shield covering from the rain 

 mid action of the atmosphere ; by this contrivance it retains its 

 legible appearance. Francis Pastorelli. 



2826d. Standard Minimum Thermometer. Wet and Bry 

 Bulb Hygrometer J mounted on a vulcanite scale. 



Francis Pastorelli. 



The maximum is constructed upon the valve principle patented by Negretti 

 and Zambra. This thermometer has in its bend near the ball a small piece 

 of solid enamel glass partly fused ; the ball and part of the stem are filled with 

 mercury, the upper part is a vacuum, the piece of enamel glass acts as a 

 valve, for by applying heat to the mercury ball,,the mercury in expanding 

 passes the enamel glass (but it cannot return on cooling), it registers the 

 amount of heat applied, which is read at the upper end of the column. 



