448 Appendix to Dr. Blagden ’s Report 
first. These contradictory facts may, I apprehend, be ac- 
counted for in the following manner. The mechanical ope- 
ration of grinding a stopper that will fit so delicate a tube, as 
is here necessary, perfectly tight, must be acknowledged to be 
difficult ; and should it happen to be done accurately, so that 
none of the fluid is lost in one degree of temperature, it is very 
doubtful whether, on exposing this instrument to a different 
temperature, the expansion would be the same in both the 
tube and stopper. It appears most probable, from these ex- 
periments, that they actually did not expand alike, as perhaps 
no two pieces of glass ever do ; and the effect to be expected 
from a less expansion of the stopper than of the tube is, either 
that some of the fluid would leak out, or that the capacity of 
the ball would be enlarged. But the chief reason why there 
may sometimes seem to be a loss, at other times no loss at 
all, I apprehend to be, that more of the fluid will adhere to 
the upper part of the tube, on filling it, at one time than at 
another. In the use of this instrument also, a small error may 
arise from the stopper not being always put in exactly alike ; 
in which case the capacity of the instrument would be altered 
and, of course, the divisions on its stem would not give the 
expansion of the fluid accurately. Care was always taken 
in these experiments to put the stopper in as nearly alike as 
possible ; but it might not perhaps always be done exactly so.. 
It is also obvious, that experiments with this instrument will 
be affected by another source of error, if made in the manner 
which is recommended, namely, by heating the fluid up from 
6 o° to ioo°, and cooling it down again to 30° : for it must be 
evident that the whole length of the tube will then be left 
wet by the fluid, in sinking from too 0 to 30°, and conse-* 
