MR. J. B. HANNAY ON A NEW CALORIMETER. 243 



by the usual non-conducting material, we can have a large 

 rise of temperature in a considerable space of matter. Of 

 course at the present time, when the specific heat of sub- 

 stances such as silver, copper, and iron have been very 

 accurately determined, we do not need to have a water or 

 absolute calorimeter, but only an instrument which will 

 accurately register the rise of temperature, and the value 

 of whose graduations may be determined by standard 

 metals ; so that although we do not know the absolute 

 calorimetric value of the heat communicated to the air 

 and glass of such an instrument, yet, if its indications are 

 proportional to the amount of heat communicated, we 

 have all that is required to form a relative calorimeter. 



Then as to the construction of such an instrument. It 

 was found that the use of ground joints in the instrument 

 might be entirely avoided, as a red india-rubber stopper 

 can be adjusted with nearly as much accuracy as a ground 

 joint. 



The apparatus shown below as fig. i is the first form of 

 the calorimeter I constructed. A ring was etched near 

 the top of the wide outer tube, which was then filled with 

 water and the india-rubber stopper pressed in till it was 

 level with the ring (the excess of water escaping by the 

 index-tube) and the whole weighed. This was repeated 

 several times ; and it was found that (provided the tem- 

 perature were constant) the weights differed only by two 

 or three centigrammes at the most. If, however, the 

 stopper were permanently fixed in, and the index-tube and 

 thermometer and interior tube pushed into their proper 

 marks afterwards, the weights differed only by a few 

 milligrammes. It was thus seen that the volume of gas in 

 the apparatus could be adjusted with as great accuracy as 

 by ground stoppers and with less chance of leakage. 



The apparatus consists, then, of a wide outer tube having 



r2 



