Mercurial Thermometer

—Consists a stem or tube of gla , formed with a bulbous expansion at the foot to contain the mercury which expands into the tube. A sufficient quantity of mercury having been introduced, it is boiled to expel air and moisture, and the tube is hermetically sealed. The freezing and the boiling points on the scale are then determined, respectively, by immersing the thermometer in melting ice, and afterwards in the steam of water boiling under the mean atmospheric pre ure, 14.7 pounds per square inch, and finally marking the two heights of the column of mercury in the tube. The interval between these two points is divided into 180 degrees for Fahrenheit’s scale, or 100 degrees for the Centigrade scale, and degrees of the same interval are continued above and below the stanard points as far as may be nece ary.