Thus Euclidean geometry does not hold in the gravitational field even in the first approximation, if we conceive that one and the same rod independent of its position and its orientation can serve as the measure of the same extension. But a glance at (70a) and (69) shows that the expected difference is much too small to be noticeable in the measurement of earth’s surface. We would further investigate the rate of going of a unit-clock which is placed in a statical gravitational field. Here we have for a period of the clock _ds_ = 1, _dx₁_ = _dx₂_ _dx₃_ = 0; then we have 1 = _g₄₄__dx₄²_ _dx₄_ = 1/√(_g_₄₄) = 1/√(1 + (_g_₄₄ - 1)) = 1 - (_g_₄₄ - 1)/2 or _dx₄_ = 1 + _k_/8π ∫ ρ_d_τ/_r_. Therefore the clock goes slowly what it is placed in the neighbourhood of ponderable masses. It follows from this that the spectral lines in the light coming to us from the surfaces of big stars should appear shifted towards the red end of the spectrum. Let us further investigate the path of light-rays in a statical gravitational field. According to the special relativity theory, the velocity of light is given by the equation -_dx₁²_ - _dx₂²_ - _dx₃²_ + _dx₄²_ = 0; thus also according to the generalised relativity theory it is given by the equation (73) _ds²_ = _g__{μν} _dx__{μ} _dx__{ν} = 0. If the direction, _i.e._, the ratio _dx₁_ : _dx₂_ : _dx₃_ is given, the equation (73) gives the magnitudes _dx₁_/_dx₄_, _dx₂_/_dx₄_, _dx₃_/_dx₄_, and with it the velocity, √((_dx₁_/_dx₄_)² + (_dx₂_/_dx₄_)² + (_dx₃_/_dx₄_)²) = γ, in the sense of the Euclidean Geometry. We can easily see that, with reference to the co-ordinate system, the rays of light must appear curved in case _g__{μν}’s are not constants. If _n_ be the direction perpendicular to the direction of propagation, we have, from Huygen’s principle, that light-rays (taken in the plane (γ, _n_)] must suffer a curvature ∂λ/∂_n_. Let us find out the curvature which a light-ray suffers when it goes by a mass M at a distance Δ from it. If we use the co-ordinate system according to the above scheme, then the total bending B of light-rays (reckoned positive when it is concave to the origin) is given as a sufficient approximation by B = ∫_{-∞}^∞ ∂γ/∂[_x_]₁ _dx₂_ where (73) and (70) gives γ = √(-_g₄₄_/_g₂₂_) = 1 - α/2_r_ (1 + _x₂²_/_r²_). The calculation gives B = 2α/Δ = KM/2πΔ. A ray of light just grazing the sun would suffer a bending of 1·7″, whereas one coming by Jupiter would have a deviation of about ·02″.