Now, by (13) and (14) we have:
∂
H
′
∂
y
˙
′
=
∂
H
′
∂
y
˙
∂
y
˙
∂
y
˙
′
=
∂
H
′
∂
y
˙
c
c
2
−
v
2
c
2
+
v
x
˙
′
=
∂
∂
y
˙
(
H
′
c
2
−
q
2
c
2
−
q
′
2
)
{\displaystyle {\frac {\partial H'}{\partial {\dot {y}}'}}={\frac {\partial H'}{\partial {\dot {y}}}}{\frac {\partial {\dot {y}}}{\partial {\dot {y}}'}}={\frac {\partial H'}{\partial {\dot {y}}}}{\frac {c{\sqrt {c^{2}-v^{2}}}}{c^{2}+v{\dot {x}}'}}={\frac {\partial }{\partial {\dot {y}}}}\left(H'{\sqrt {\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}}\right)}
(23)
and:
d
t
′
d
t
=
c
2
−
v
x
˙
c
c
2
−
v
2
{\displaystyle {\frac {dt'}{dt}}={\frac {c^{2}-v{\dot {x}}}{c{\sqrt {c^{2}-v^{2}}}}}}
.
It follows:
d
∂
∂
y
˙
(
H
′
c
2
−
q
2
c
2
−
q
′
2
)
=
d
∂
H
∂
y
˙
{\displaystyle d{\frac {\partial }{\partial {\dot {y}}}}\left(H'{\sqrt {\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}}\right)=d{\frac {\partial H}{\partial {\dot {y}}}}}
and by integration:
∂
∂
y
˙
(
H
′
c
2
−
q
2
c
2
−
q
′
2
)
=
∂
H
∂
y
˙
{\displaystyle {\frac {\partial }{\partial {\dot {y}}}}\left(H'{\sqrt {\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}}\right)={\frac {\partial H}{\partial {\dot {y}}}}}
, ebenso:
∂
∂
z
˙
(
H
′
c
2
−
q
2
c
2
−
q
′
2
)
=
∂
H
∂
z
˙
{\displaystyle {\frac {\partial }{\partial {\dot {z}}}}\left(H'{\sqrt {\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}}\right)={\frac {\partial H}{\partial {\dot {z}}}}}
.
(24)
The constant of integration, an absolute constant, vanishes because only q' = q H' goes over into H .
Now, the four equations (19) and (24) give by integration:
H
′
c
2
−
q
2
c
2
−
q
′
2
=
H
+
c
o
n
s
t
{\displaystyle H'{\sqrt {\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}}=H+const}
.
The constant does not depend on V, T,
y
˙
,
z
˙
{\displaystyle {\dot {y}},{\dot {z}}}
; but it can still depend on
x
˙
{\displaystyle {\dot {x}}}
, or by (14),
c
2
−
q
2
c
2
−
q
′
2
{\displaystyle {\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}}
. We therefore write:
H
′
c
2
−
q
2
c
2
−
q
′
2
=
H
+
f
(
c
2
−
q
2
c
2
−
q
′
2
)
{\displaystyle H'{\sqrt {\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}}=H+f\left({\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}\right)}
and determine the most general expression of the function f .
At first, we have:
H
′
c
2
−
q
′
2
−
H
c
2
−
q
2
=
1
c
2
−
q
2
⋅
f
(
c
2
−
q
2
c
2
−
q
′
2
)
{\displaystyle {\frac {H'}{\sqrt {c^{2}-q'^{2}}}}-{\frac {H}{\sqrt {c^{2}-q{}^{2}}}}={\frac {1}{\sqrt {c^{2}-q^{2}}}}\cdot f\left({\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}\right)}
.
(25)
Since the function H only depends on q, V and T , and since V' and T' are only connected to V and T by the relations (17), then the right-hand side of the equation as well as the left-hand side, are of the form:[ 1]
1
c
2
−
q
2
⋅
f
(
c
2
−
q
2
c
2
−
q
′
2
)
=
Q
′
−
Q
{\displaystyle {\frac {1}{\sqrt {c^{2}-q^{2}}}}\cdot f\left({\frac {c^{2}-q^{2}}{c^{2}-q'^{2}}}\right)=Q'-Q}
,
↑ This can be seen in the most simple way, when we take an arbitrary value q" and sum up the three expressions
H
′
c
2
−
q
′
2
−
H
c
2
−
q
2
,
H
″
c
2
−
q
″
2
−
H
′
c
2
−
q
′
2
{\displaystyle {\frac {H'}{\sqrt {c^{2}-q'^{2}}}}-{\frac {H}{\sqrt {c^{2}-q{}^{2}}}},{\frac {H''}{\sqrt {c^{2}-q''^{2}}}}-{\frac {H'}{\sqrt {c^{2}-q'^{2}}}}}
and
H
c
2
−
q
2
−
H
″
c
2
−
q
″
2
{\displaystyle {\frac {H}{\sqrt {c^{2}-q^{2}}}}-{\frac {H''}{\sqrt {c^{2}-q''{}^{2}}}}}
.