296  Joty—On the Volume Change of Rocks and Minerals attending Fusion. 
1200°. The bead breaks up then by the formation of bubbles which apparently 
rise by gravity within it, blowing out generally at its higher surface. Figure 7 
is copied as accurately as possible from two photographs of the image of an augite 
bead at 15° C. and at 1120° C., the photographs being successively printed on 
the one surface. Transparent liquid beads of salts, such as potassium carbonate, 
can be observed, presenting the singular appearance of a transparent red hot liquid ; 
revealing, in fact, the extremity of the suspending wire within. 
The fact must not be forgotten in further considering the lability to error 
from this source, that a change of surface tension will cause no error so far as 
gravitational effects are concerned, provided this change does not mean reduction 
of surface tension below a certain amount, that requisite to secure the retention of 
the spherical form against the weight of the bead. In many familiar cases, 
substances at high temperatures and perfectly liquid show that they possess con- 
siderable surface energy. The rounding of shot grains is effected against very 
