Intelligence a7id Miscellanecnis Articles. \ 73 



Dr. Rutherford's registering thermometer, and Dr. Mason's wet and 

 dry bulb hygrometer. 



ITie complete instrument consists of four thermometers, two max- 

 ima and two minima, which can be litted on one or two separate 

 frames ; with separate frames I take for the first. 



Two spirit thermometers, with indexes as commonly made for the 

 minima thermometers, graduated on their tubes to degrees and half- 

 degrees ; the reservoirs at the tops of the tubes I cover with small 

 metallic caps, to prevent condensation of the spirit therein* ; one df 

 these tubes has the bulb covered with silk, the other left bare, but 

 the colour of the two bulbs made to approximate, as far as practica- 

 ble, like Leslie's hygrometers. 



The two tubes are then fastened on a frame, the wet bulb about 

 three inches below the dry, and the tubes parallel, thus : 



Cap. 



Dry. 



Wet. 



The dotted line shows the position of the bird's water-fountain, 

 which is concealed at the back of the frame : the extreme dimen- 

 sions of the frame are twelve inches long by four and a half deep. 



The second frame is arranged in precisely the same way with the 

 two maxima tubes : if they are intended for the sun's rays, they 

 are vacuum-fiUedf. 



It will be evident these frames supply us with the common ther- 

 mometer, niaxima and minima thermometers. Mason's hygrometer ; 

 and, in addition, the wet and dry minima tubes give in most cases 

 the dew-point at the time of minimum temperature, while the max- 



* I have found small caps of tinfoil sufficient to prevent, in a spirit ther- 

 mometer exposed to two months' summer sun, the condensation of the 

 spirit in the upper part of the tube. I need scarcely mention, that under 

 similar circumstances, without a metallic cap, spirit would condense in a 

 Jew hours after a hot sun. 



t To fill mercury-registering thermometers with the upper part of the 

 tube, a vacuum is the readiest mode I know to get them to work correctly 

 in the sun ; at all events, it is certain oxygen must not be present, for the 

 sun s rays are an irresistible source of chemical action betwixt mercury and 

 oxygen. I have a tube that has worked unimpaired for eight months in 

 the sun. ° 



I should mention, that it was Prof. Lloyd of Trinity College, Dublin 

 who noticed to me in March last the liability there would be to error iri 

 the registers of ma.ximum and minimum temperatures, and their respective 



