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MR. J. B. HANNAY ON A NEW CALORIMETER. 



glass bulbs (one holding an interior tube for the reception 

 of the substances, and the other a little smaller in diameter 

 in order that its cubic contents may be about the same) 



Fig. 2. — The Differential Calorimeter. 



are fitted with an index-tube of small bore, as shown in 

 the figure, which is graduated between the two small 

 cavities on the upper portion of the tube, the cavities being 

 there to prevent the index being accidentally drawn into 

 either of the bulbs. The two bulbs are placed in a box 

 (indicated by dotted lines) surrounded by non-conducting 

 material, and the instrument is ready at any time for use. 

 A thermometer is placed between the bulbs in order that 

 the temperature may be noted at which the experiment was 

 tried. In the instrument No. i the indications are nearly 

 proportional to the specific heat of the substance ; but in 

 the second or differential calorimeter a curve should be 

 drawn of the values for known metals, just as is done for 

 the spectroscopic scale, and the specific heats of the bodies 

 reduced by reference to the curve. To show the accuracy 



