HAMMOND-HERSCHEL. 
102 
essential singularity of function, iv, 105; central forces problem, iv, 520; hodograph, iv, 520; 
transformation of coordinates, iv, 558—9, 588; ray systems, vra, 504, xn, 571—5; surface orthogonal 
to set of lines, ix, 587; system of differential equations, x, 113—8; equations of central orbit, 
x, 613; on mathematics, xi, 431; algebra and time, xi, 443; conical refraction, xi, 449; multiple 
algebra, xii, 460, 466, 474—5; Sylvester on Hamiltonian numbers, xm, 48; (see also Differential 
Equations). 
Hammond, J.: theory of tamisage, xi, 409—10; seminvariants, xn, 253; Sylvester’s reciprocals, xm, 
47—8, 381, 388; on Hamiltonian numbers, xm, 48. 
Hansen, P. A.: lunar theory, hi, 13—24, 291—2; elliptic orbit, hi, 95; expansion of true anomaly, 
m, 140; planetary theory, hi, 26S—9, ix, 180—3; disturbed elliptic motion, hi, 270—1; disturbing 
function in lunar theory, hi, 293, 319—43; variation of plane of planet’s orbit, hi, 516—8; elliptic 
motion, iv, 522, 523, 588; relative motion, iv, 536, 588; pendulum, iv, 541, 588; spheroidal 
trigonometry, ix, 197. 
Hargreave, C. J. : on differential equations, viii, 458. 
Harley, R.; equation of differences, iv, 241, 245; symmetric products and quintics, iv, 310—13; 
quintics, v, 53; a differential equation, vn, 354; theory of equations, xi, 520; invariants, xn, 
390—1. 
Harmoconic: defined, v, 342. 
Harmonic Relations: of two lines or points, n, 96—7; theory of, and two or more quadrics, n, 
529—40. 
Harmonics: symmetric, n, 555; inscribed, hi, 113; reciprocal lines, xm, 58—9; and non-Euclidian 
geometry, xm, 482—9. 
Harriot, T.: mathematical discoveries, xi, 437. 
Hart, A. S.: cubic curves, iv, 499; relative motion, iv, 535; triple tangent planes, vi, 372, 375; 
nine-point circle, xm, 548. 
Haughton, S.: inertia, iv, 564—5, 588. 
Haupttangenten: (inflexional tangents), viii, 157. 
Heal, W. E.: bitangents of quintic, xm, 21. 
Hearn, G. W.: on a geometrical locus, i, 496; quartic curves, i, 496; quadric curves, v, 262. 
Heath, R. S.: non-Euclidian geometry, xm, 481, 499. 
Helmholtz, H. von: hydrodynamical equations, xm, 6—8. 
Hemihedron: the word, x, 328. 
Hemipolyhedron: the word, x, 328. 
Hensley, P. J.: foci of conics, iv, 505—9. 
Heptacron (see Polyacra). 
Heptagon : construction, x, 609. 
Hermite, C.: homographic transformation of quadric into itself, n, 107; elliptic integral and covar 
iants of quartic, n, 191; law T of reciprocity, n, 232, 234; skew invariant of quintic, n, 233; 
transformation of quadric function, n, 499; hyperdeterminants, n, 598—601; elliptic integrals, 
iv, 68—9; ternary cubics, iv, 326, 330; Tschirnhausen’s transformation, iv, 364—7, 375, vi, 165, 
170; automorphic transformation, iv, 416; elliptic functions and solution of quintic, iv, 484—9; 
matrices, v, 438, xii, 367—70, 386; quantics, vi, 147; quintic equation, vi, 170; nodal cubic, vi, 
174—6; canonical form of quintic, vi, 177—83; transformation of elliptic functions, vn, 44, ix, 
113, xii, 337, 416—7, xm, 31, 39; reduction of Abelian integrals, x, 214; concomitants of ternary 
cubic, xi, 342; elliptic functions, xi, 452; theory of equations, xi, 520; Abelian functions, xii, 
98; transformation of double theta functions, xii, 358; //-product theorem, xii, 584—6; cubic 
equations, xm, 349; omega functions, xm, 558. 
Herschel, Sir J. F. W.: finite differences, iv, 95, 107, 262; Brinkley’s formulae, x, 58—9; difference 
table, xi, 144.