450 
ASTRONOMY: C. E. ST. JOHN 
two lines, which coincide if 
hh - = 0. 
But this requires the Hessian to have a double point; therefore the gen- 
eral quartic cannot have a polar conic made up of two coincident lines. 
Also the polar cubic of (0, 0, 1) is 
a^XQ^ + MxqHi + ?>gXQH2 + ()nx^iX2 + ?>c 0X0X2"^ + ?>CiX2^ + 0X2^ = 0. 
This can have a cusp only if 
c,l _ ^2 ^ 0. 
This has clearly nothing to do with 6 = 0, the condition that r^o be a 
stationary line of the quartic. Therefore the cusps of the Steinerian do 
not lie on the stationary lines, as might be expected from their number 
— twenty-four, w = 0 is the condition that X2 = 0 be the tangent to 
the Hessian; then the cusp cannot be obtained by making Ci — 0, for 
then the Hessian has a double point. Putting / = 0 shows that the 
cusp tangent is also the tangent to the Hessian. Use of w = 0 also shows 
that the polar points of lines of the Cayleyan as to {t^^ lie on the corre- 
sponding tangents to the Hessian. 
A SEARCH FOR AN EINSTEIN RELATIVITY-GRAVITATIONAL 
EFFECT IN THE SUN 
By Charles E. St. John 
MOUNT WILSON SOLAR OBSERVATORY. CARNEGIE INSTITUTION OF WASHINGTON 
Communicated by G. E. Hale, June 5, 1917 
From the equivalence principle of generalized relativity Einstein^ 
concludes that the propagation of light is influenced by gravitation, and 
deduces two important consequences that can be subjected to the test 
of observation; namely, a train of light waves passing close to the edge 
of the sun is refracted so that the angular distance of a star appearing 
near the sun is increased by V'.IS, and the Fraunhofer lines are displaced 
to the red in the solar spectrum by an amount equivalent to a velocity 
of recession of 0.634 km/sec. The amount depends only on the dif- 
ference in gravitational potential between the gravitation field in which 
the radiation originates and the field where it is received. In the case 
of massive stars with density comparable to that of the sun the Kne 
displacement may be large, equivalent to 0.634 km/sec. M d where 
M and d are in terms of the sun's mass and density.^ Confirmation of 
either of these consequences would have not only an important bearing 
upon the establishment of the relativity principle but also upon the in- 
