36 
MR. FARADAY ON THE 
the metal. This circumstance was the principal occasion of the advantages 
afforded by the use of the underlying plate being given up. 
78. The heat which has to be borne during the operation of stirring, 
is very considerable, especially upon the hands ; but at such a moment 
no retreat from the w6rk, because of mere personal inconvenience, can be 
allowed. But the circumstance renders the use of a cover for the stirring hand 
very advantageous. I have found a loose linen bag, into which the hand could 
go freely, more convenient for this purpose than a glove ; for being in contact 
with the skin at distant parts only, the hand is preserved at a much lower 
temperature. Two small holes in it, one at the front and the other at the top, 
allow the handle of the stirrer to pass obliquely through, by which arrange- 
ment it is easily held with firmness, and the bag itself prevented from slipping 
towards the glass. It should not be larger than to cover the wrist, or it will 
embarrass the movements ; and it should be very stiffly starched, and ironed, 
that no fibrous particles may fly from it to the glass during the stirring. 
79. The glass which, adhering to, is brought away with the stirrer, indicates, 
by its appearance, the general character and state of that in the tray; but 
during its examination, the experimenter must carefully refrain from touching 
it; for if the finger, or any other ordinary organic substance, come into contact 
with it, the next time the instrument is immersed in the ignited glass, the part 
touched Anil produce bubbles. It is therefore of importance that the stirrer 
be preserved perfectly clean from one stirring to another, for which purpose it 
may be deposited so that the platina shall be received in an evaporating basin, 
the mouth of Avhich is afterwards covered over. 
80. In entering upon the considerations relative to the bubbles, it will be 
evident, from the nature of the materials and the quantity of elastic matter 
originally present, that these are at first very numerous. The larger ones soon 
ascend to the surface, and breaking, are dissipated without inconvenience ; 
but the smaller ones rise with far less readiness, and the smallest have 
so little power of elevation, that the general currents in the liquid appear 
sufficient to carry them downwards, or in any other direction, and thus retain 
them for any period within the mass. A useful idea of the length of time 
required for very minute bubbles to ascend through a fluid having some tena- 
