Joty—On the Volume Change of Rocks and Minerals attending Fusion. 285 
dimension of the object. The numbers quoted in this example by no means 
representing the final limits to which the measurements in the case of more 
suitably shaped bodies could be pushed, it will be seen that over wide ranges of 
temperature very reliable curves of expansion are attainable, supposing that the 
determination of temperature is equally reliable. 
The accompanying figure (fig. 1) shows the arrangement for supporting and 
heating the object. The platinum oven 
is carried between two stout brass for- 
ceps supported upon pillars of glass. 
The current passes from forceps to 
forceps, traversing the platinum oven. 
The forceps carry each a shallow cup 
placed on the summit of the pillars in z 
which a little mercury is poured. The ~~ Ae 
wires conveying the current dip into 
these cups. A fine wire will be noticed spanning the space between the pillars. 
This wire is for the purpose of suspending the minute fragment of substance 
in such a manner that when heated it may not shift laterally in the field of 
the microscope. The wire is in fact carried at each extremity upon flat vertical 
springs. These rise from the base of the pillars and pass through holes slotted in 
the forceps. Each spring is finely notched at its upper extremity, and the crossing 
wire is a short length of platinum wire which has been fused at each extremity 
in the oxyhydrogen flame, its extremities being beaded with the fused platinum, 
and the length of the wire is adjusted in the flame, so that it is stretched by the 
springs when fitted across the notches in the latter. Any thermal 
change of length of the wire, due to the high temperature of the 
oven immediately beneath it, will be attended by the equal 
yielding of both springs laterally, and the central point of the 
cross wire will not shift. 
At the central point of the cross wire the substance hangs. The 
ribbon forming the oven is also adjusted till the slit-like opening 
into the tube is beneath this central point. The tube of the oven 
is closely 2°3 millimetres in diameter. The manner of folding 
the ribbon is explained by the figure. A small globule of once 
melted and again solidified orthoclase is seen hanging within the 
oven. 
The mode of suspending this globule requires an enlarged 
figure for explanation (fig. 2). The bead is attached by fusion to 
a fine platinum wire. This wire is turned over in a sharp bend so that the cross 
wire described above is somewhat pinched in the bend. This friction on the cross 
VAD. 
Fig, 2. 
