Joty—On the Conservation of Mass. 29 
being run into the warmed tube, this quantity can be chased about the tube 
by waving it over a low flame, into any required position. The quantity used 
must be no more than will give a plug at the bend of a length hardly greater 
than the internal diameter of the tube. Otherwise there is risk that the plug on 
heating will not break down, but simply shift its position. Or the plug may be 
placed in the rectangular bend most remote from the upper vessel, when a very 
small quantity suffices. 
The foregoing arrangement for bringing the reacting substance together has 
worked most satisfactorily. The method which would at first suggest itself would 
be to use the heating effect of a current conveyed to the vessels along the beam, 
and entering at mercury contacts at the centre of the beam. This was actually 
tried and used for some time. In this case, the fusible plug was carried in the 
connecting tube just above x, and was melted by a current circulating in a 
platinum wire surrounding it. None of the results given later are obtained with 
this arrangement. It was found that the effects of the contacts were not constant, 
but depended upon the cleanliness of the mercury surfaces to a degree which 
introduced a very variable resistance to the swinging of the beam, A perfect 
adjustment of the iron wire points entering the mercury cups beneath the centre 
of the beam, so that there was perfect alignment with the suspension, would doubt- 
less have permitted of make and break of contact without disturbance of the 
vibrations; but such alignment was never attained, and evidently would be most 
difficult to arrive at. It being found difficult to effect make and break without 
perturbations, the contacts had to be left on during experiment; and, as I have 
stated, a variable resistance or friction introduced thereby, which finally led 
to the abandonment of the arrangement. 
The counterpoise carried at the other extremity of the beam is in the form of 
a narrow test-tube filled to a certain depth with mercury, to which more was added 
or from which some was taken according to the mass of active substances used 
in the experiment. 
The beam and its load, as described, are contained in a strongly made case of 
pine, lined with zinc, and provided with a removable front. This front is double- 
walled, the internal thickness being about4°5 cms. The space between the walls 
is filled with fine, dry shavings of wood. A cell is, however, constructed in the 
thickness of the removable front, in which the platinum heater, as already described, 
is located. This cell is closed in front by a glass window, and on the inner side 
is also glazed ; but with a horizontal slit left for the entry of the air-tube connecting 
the vessels as referred to above. The side of the wooden ease is furnished with 
another window, 5 x 10 cms., for the admission of the rays required to form an 
image, after reflection from the torsion-mirror, upon a divided scale ; the torsion- 
wire is carried in a glass tube securely affixed to the top of the case, and provided 
