133 
STROH—SURFACES. 
Stroh, E : perpétuants, xiii, 266, 301—6, 314—8. 
Study, E. : Zeuthen on, vi, 594. 
Sturm, J. C. F. : integration of dynamical equations, in, 186, 203. 
Sturm, R. : homography, vm, 200 ; correspondence of points and tetrahedra, vm, 200—8 ; root-limitation, 
ix, 39 ; theory of equations, x, 4—5, xi, 498—9, 505. 
Sturmian Constants : for cubic and quartic equations, iv, 473—7 ; for quantics, vi, 159. 
Sturmian Functions : note on, i, 306—8, 588 ; new researches, i, 392—6 ; endoscopic and exoscopic 
expressions, i, 588; tables for equations from second to fifth degrees, ii, 471—4. 
Sturm’s Theorem: vi, 159, 161; Sylvester’s work at, xm, 46. 
Subinvariants : the term, xn, 251, 273. 
Subrational: the term, ix, 315. 
Sub-regular Integrals : of differential equations, xn, 444—52. 
Substitutions : theorem relative to theory, vu, 47 ; arising from a problem in arrangements, x, 247—8 ; 
and theory of groups, x, 324—30, 401—6 ; and permutations, x, 574 ; evolution, xi, 455 ; the notion 
of, xi, 509—10, 521; Latin squares, xm, 55—7; groups for two to eight letters, xm, 117—49; 
Sylow’s theorems on groups, xm, 530—3 ; sixty icosahedral, xm, 552—7. 
Subsurface : the term, ix, 79. 
Summit: defined, v, 63, xm, 507. 
Sums : of squares, n, 49—52 ; the term, x, 186, 192 ; of two series, xm, 49—50. 
Sun: and moon’s mean motion, hi, 522—61; Newcomb on parallax, ix, 177—8; (see also Solar Eclipse). 
Supercurve : the term, ix, 79. 
Superlines : in hyperspace, ix, 79—83. 
Supp : the term, vi, 263. 
Supplement : the term, vi, 263. 
Suremain-de-Missery, A. : imaginaries, xn, 467. 
Surface, Congruence, Complex, in Ency. Brit. : xi, 628—39 ; introductory, xi, 628—9 ; surfaces in 
general : torses, xi, 629—32 ; surfaces of orders 2, 3, and 4, xi, 632—4 ; congruences and complexes, 
xi, 634—5; curves of curvature: asymptotic lines, xi, 635—6; geodesic lines, xi, 636—7; curvi 
linear coordinates, xi, 637 ; orthotomic surfaces : parallel surfaces, xi, 637—8 ; minimal surface, 
xi, 638—9. 
Surface-integral : prepotential, ix, 321—30. 
Surface of Centres : for wave-surface, xm, 248 ; (see also Ellipsoid, Centro-surface of). 
Surface of Cylinder : Archimedes’ theorem for, xn, 56—7. 
Surface of Revolution : and Mercator’s projection, vm, 567. 
Surfaces : equimomental, i, 253—4 ; wave (tetrahedroid), i, 302—5, 587 ; confocal, i, 362—3 ; singularities, 
ii, 28—32, iv, 22—7 ; theory of skew, n, 33—4 ; envelopes and parallel curves, iv, 123—33, 152—7, 
158—65 ; curvature of, iv, 466—9 ; theorem on degenerate, v, 98—9 ; developable, and prohessians, 
v, 267—83 ; planar, v, 578 ; sibi-reciprocal, vi, 21, x, 252—5 ; sextic, vi, 87—100 ; singularity of, vi, 
123—8; tetrahedral, vil, 48—53; on certain skew, vu, 54—65; Steiner’s, vu, 247; intersection of 
two, vu, 563; divisible into squares by curves of curvature, vm, 97—8, 145—6, 264—8; correspond 
ence, transformation, and deficiency, vm, 200—8 ; penultimate forms of, vm, 262—3 ; transformation 
of unicursal, vm, 388—93 ; deficiency of certain, vm, 394—7 ; reciprocal, vm, 394 ; of eighth order, 
vm, 401—3; representation on plane, vm, 538—9; families of, vm, 567 ; transformation of equation 
of, to chief axes, ix, 48—51; the term, in five-dimensional geometry, ix, 79; orthogonal to set of 
lines, ix, 587—91 ; flexure of spherical, x, 30—2 ; of minimum area, x, 63—7, xm, 41—2 ; octic, 
x, 79— 92 ; on a sibi-reciprocal (octic), x, 252—5 ; fleflecnodal planes, x, 262—4 ; Jacobian of six 
points, x, 281—93; flexure of, x, 331—2; distribution of electricity on two spherical, xi, 1—6; 
general theory, xi, 14—6, 224; deformation and flexure of, xi, 66—7, 317—22; theory of apsidal, xi, 
111—3; theory of reciprocal, xi, 225—34; contact of line with, xi, 281—93; geodesic curvature of