the specific heats of certain solids. 277 



TW' 



by representing the three terms w-{-gx-\-e by W' whence g= . ? 



(4). To this, as before stated, we must apply a correction if the 

 thermometer be not at the same temperature when immersed, as the 

 water was when the sohd was plunged into it. CaUing the differ- 

 ence d we have the correction tde, as before stated, according as 

 the thermometer was below or above the water, and hence the form- 



Tw'tde ^ ^ 

 ula becomes a; = r — (5). 



4. If the specific heat of the solid under trial and of the contain- 

 ing vessel be the same, (as when a vessel of untinned sheet iron is 

 employed to hold the water,) we may then if the specific heat be 

 supposed not to vary within the limits of our experiment, employ the 

 following expressions in which z is the specific heat of both, the 

 solid and the water vessel ; T, iv, and e remaining as in (3), we ob- 

 tain the equation itz=^li{w-\-e-^gz)=^T{iv-{-e)-^Tgz, and by 



T(w + e) 

 transposition itz — ^gz=^(w-{-e), vihence z=^- . rp ? (6). 



It g x 



5. But if, instead of making the container of the same material 

 as the body under trial, we choose to form it of any other kind, even 

 of one whose precise specific heat is not yet known, we may, by 

 using vessels of different thicknesses and the same liquid content, 

 ascertain by successive experiments under otherwise similar circum- 

 stances, the specific heat of the material which composes the vessel. 

 Thus two jars capable of containing the same weight of water may 

 be formed of glass from the same melting pot, but one possessing 

 two or three times the thickness of the other. We may then heat 

 the same mass of iron twice (or any number of times) to the same 

 temperature, and immerse it in water at the different trials in each 

 of the two vessels at the same temperature. Then putting 



w=^ the weight of water contained in each glass, 



g= the weight of the thicker glass, 



^= that of the thinner, 



0?= the unknown specific heat of glass, 



T= the change of temperature of water and glass when ^ is used, 



/= the change of temperature of iron when g is used, 



T'= the change of temperature of water when g' is used, 



t'= the change of temperature of iron when g* is used, 



», as before, = the weight of iron, 



