455 
on Spirituous Liquors ► 
with that kind of instrument which has a tube rising from the 
side of the ball, to be closed with a stopper. More accuracy 
may undoubtedly be expected from experiments made with 
the other kind of instrument which has two tubes, because 
one of the inconveniences attending the former is removed in 
it : but we have seen that even experiments made with this 
instrument do not bear the same marks of accuracy as the ex- 
periments by weight ; nor can this be much wondered at, if it 
be considered that the trifling error of ,027 of an inch, in con- 
structing the instrument, will produce an error of one division, 
which is equal to 0,24 of a grain on the quantity contained in 
our weighing-bottle ; and how difficult and uncertain it is in 
such an instrument to ascertain the exact temperature, by 
placing a thermometer only by the side of it. It is not un- 
common to see the fluid in the expansion instrument, and the 
mercury in the thermometer, move contrary ways : and I have- 
more than once observed an alteration in the thermometer, of 
more than half a degree, when no alteration whatever has 
been produced in the fluid in the expansion instrument. In- 
deed, on the least reflection it must be obvious to every one, 
that the changes of temperature of the fluid in a ball of 1^ 
inch diameter, cannot be expected to be so quick as in one of 
0,22 of an inch. It is also of the utmost consequence in making 
experiments with this instrument, though it will render it ex- 
tremely tiresome to the experimenter, that it be in continual 
motion ; for should that precaution not be observed, very con- 
siderable errors indeed will take place. 
I am, &c. 
Apartments of the Royal Society, 
Somerset Place. G. GILPIN. 
3N 2 
