Joty—On the Conservation of Mass. 20 
material; in other words, the result is independent of the mass of active sub- 
stance taken. The experiment may therefore be carried out on a large or small 
scale, as other circumstances may dictate. 
In the foregoing calculation, the conditions are such as would obtain with the 
use of a torsion-balance, the active substances being carried on a beam of con- 
siderable length. We may seek for the inertia-effect in other ways. ‘Thus 
obviously the use of a sensitive chemical balance, observed during the reaction, 
and at such times that the meridian circle of the observer is approximately 
tangential to the Earth’s orbit, should reveal a temporary apparent change of 
weight. The benefit of a continued acceleration would be lost, however, 
and the method exposed to errors of temperature in an exaggerated degree, as 
well as to errors arising from loss or gain of material. Errors from the latter 
source do not affect the torsion-balance method. Again, the reacting substances 
may be enclosed in the bob of a sensitive pendulum. This method has the great 
advantage of not requiring the added inertia of the counterpoise. On the other 
hand, however, the range of motion is so small under the constraining effect of 
the weight-force attending deflection that, with any reasonable length of suspen- 
sion, tremors of small magnitude arising from external sources or from the 
internal motions attending the mixing of the chemicals would mask the true 
effects. After full consideration the torsion-balance method’was adopted in the 
experiments to be now described. 
The arrangements at first made were modified in several particulars as diffi- 
culties arose. It is needless to do more than refer to those now in use, and by 
which the results given in this paper have been obtained. 
The torsion-beam is constructed of straws ; taking the form of a king-post truss 
(the king-post being above the horizontal member). ‘The component straws meet 
in corks to which they are attached by glue. The horizontal member is 25 cms. 
long; the king-post 10 cms. The weight of the beam, inclading a galvanometer- 
mirror, is 2°5 grammes. This beam carries 100 grammes at each extremity 
without serious flexure. The suspending wire is of phosphor-bronze, ribbon- 
section. Its breaking weight is 355 grammes. It is attached by soft solder to 
a wire which passes axially right through the king-post and diametrally through 
the horizontal member of the beam. 
After trying various lengths of suspension, finally a length of 30 cms. was 
adopted. In some respects a still shorter one would be desirable. Owing to the 
bulky nature of the suspended vessel, convection currents are particularly trying ; 
and with this length of suspension, a zero position is never assumed, and indeed is 
not accurately determinable. Somewhat greater restraint arising from the tor- 
sion moment of the suspension would not affect the limits of accuracy obtainable 
in practice. 
