He remarks that, in
all its generality, the law may be translated thus: If the isothermal
diagrams of two substances be drawn to the same scale, taking as unit
of volume and of pressure the values of the critical constants, the
two diagrams should coincide; that is to say, their superposition
should present the aspect of one diagram appertaining to a single
substance. Further, if we possess the diagrams of two bodies drawn to
any scales and referable to any units whatever, as the changes of
units mean changes in the scale of the axes, we ought to make one of
the diagrams similar to the other by lengthening or shortening it in
the direction of one of the axes. M. Amagat then photographs two
isothermal diagrams, leaving one fixed, but arranging the other so
that it may be free to turn round each axis of the co-ordinates; and
by projecting, by means of a magic lantern, the second on the first,
he arrives in certain cases at an almost complete coincidence.
This mechanical means of proof thus dispenses with laborious
calculations, but its sensibility is unequally distributed over the
different regions of the diagram.
Pages:
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160