in. SPECIAL THERMOMETERS. 575 



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

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



Professor Ebermayer, Aschaffenbur g '. 



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

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



282 6b. Metallic Maximum and Minimum Thermometers, 



with electric alarum and battery. Baur and Haebe, Stuttgart. 



2826c. Standard Maximum Thermometer with divisions 

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

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

 legible appearance. Francis Pastorelli. 



2826d. Standard Minimum Thermometer. Wet and Dry 

 Bulb Hygrometer ; 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 j 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. 



To set this thermometer for a new observation hold the ball doAvuwards 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 will 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. 



2826 e. A 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. L. Casella. 



