Here is the experiment in brief for those uninitiated : http://media.uws.ac.uk/~davison/labpage/leedisk/leedisk.html My question is, when the steady state has been obtained (heat flowing into Brass Disc = heat flowing out of it), why do we remove the upper Brass Base and then heat the disc? Why not with it? We need to find the value of rate of fall of temperature at the steady state temperature T1 ; if we remove the Brass Base, are we not changing our initial conditions, since now the glass will be in direct contact with air, an extremely poor conductor, while in the other case it would have been in contact with Brass. Is it because while obtaining the steady state, heat is flowing out of Base only in the downward direction, and we want the same to happen for the cooling curve? If so, why? Thanks!