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- Sabatier or Sabattier effect – Sabatier, first name unknown
- Sachs–Wolfe effect – Rainer Kurt Sachs and Arthur Michael Wolfe
- Saffir–Simpson Hurricane Scale – Herbert S. Saffir and Robert ("Bob") Simpson
- Sagnac effect – Georges Sagnac
- Saha ionization equation (a.k.a. Saha-Langmuir equation) – Megh Nad Saha (মেঘনাদ সাহা) (and Irving Langmuir)
- St. Elmo's fire – Erasmus of Formiae
- Salem number – Raphaël Salem
- Sapir–Whorf hypothesis – Edward Sapir and Benjamin Whorf
- Sasakian manifold, metric – Shigeo Sasaki
- Say's law – Jean-Baptiste Say
- Scheerer's phenomenon (Blue field entoptic phenomenon) – Richard Scheerer
- Schering Bridge – Harald Schering
- Schild plot, regression analysis – Heinz Otto Schild
- Schottky effect – Walter H. Schottky
- Schröter effect – Johann Hieronymus Schröter
- Schülen–Wilson effect – see Wilson effect, below
- Schuler period, tuning – Maximilian Schuler
- Schumann–Runge bands – Victor Schumann and Carle David Tolmé Runge
- Schwarzschild effect, metric, radius – Karl Schwarzschild
- Scott effect – Elizabeth L. Scott
- Searl effect – John R. R. Searl
- Secchi (stellar) class, depth, disk – Pietro Angelo Secchi
- Seebeck effect – Thomas Johann Seebeck
- Seiberg–Witten gauge theory – Nathan Seiberg and Edward Witten
- Seiberg–Witten invariant – Nathan Seiberg and Edward Witten
- Sertoli cells – Enrico Sertoli
- Serre duality – Jean-Pierre Serre
- Seyfert galaxy – Carl Keenan Seyfert
- Shapiro effect – Irwin Shapiro
- Shimizu–Morioka equations – Tatsujiro Shimizu and N. Morioka
- Shubnikov–de Haas effect – Wander Johannes de Haas and Lev Vasiljevich Shubnikov
- Sieberg tsunami intensity scale – August H. Sieberg
- Sieberg–Ambraseys tsunami intensity scale – August H. Sieberg and Nicholas N. Ambraseys
- Simmons–Smith reaction – Howard Ensign Simmons, Jr.
- Simpson's paradox (a.k.a. Yule–Simpson effect) – Edward H. Simpson (and Udny Yule)
- Simroth's organs – Heinrich Rudolf Simroth
- Smale's horseshoe – Stephen Smale
- Smale–Rössler theorem – Stephen Smale and Otto Rössler
- Smith–Waterman algorithm – Temple F. Smith and Michael S. Waterman
- Snell's law – Willebrord van Roijen Snell
- Soloviev tsunami intensity scale – Sergey L. Soloviev
- Sommerfeld–Kossel displacement law – Arnold Sommerfeld and Walther Kossel
- Sørensen similarity index, similarity coefficient – Thorvald Sørensen
- Spörer's law, Spörer Minimum – Gustav Spörer
- Staebler–Wronski effect – David L. Staebler and Christopher R. Wronski
- Stark effect (a.k.a. Stark-Lo Surdo effect) – Johannes Stark (and Antonino Lo Surdo)
- Stark ladder (a.k.a. Wannier-Stark ladder, q.v.) – Johannes Stark and Gregory Hugh Wannier
- Stark–Einstein law – Johannes Stark and Albert Einstein
- Stebbins–Whitford effect – Joel Stebbins and Albert Edward Whitford
- Stefan's constant, law (a.k.a. Stefan-Boltzmann constant, law) – Jožef Stefan (and Ludwig Boltzmann)
- Stensen's duct – Niels Stensen
- Stern–Levison parameter – S. Alan Stern and Harold F. Levison
- Stevens effect – J. C. and Stanley Smith Stevens
- Stevens' power law – Stanley Smith Stevens
- Stewart's organs – Charles Stewart
- Stewart-Tolman effect – Thomas Dale Stewart and Richard Chace Tolman
- Stirling number – James Stirling
- Stokes radius – George Gabriel Stokes
- Stokes shift – George Gabriel Stokes
- Stolper–Samuelson theorem – Paul Samuelson and Wolfgang Stolper
- Strömgren age, photometry, sphere – Bengt Georg Daniel Strömgren
- Strömgren-Crawford photometry – Bengt Georg Daniel Strömgren and David L. Crawford
- Stroop effect – John Ridley Stroop
- Strouhal number – Vincenc Strouhal
- Stückelberg action – Ernst Carl Gerlach Stueckelberg
- Sturgeon's law – Theodore Sturgeon
- Sturmian trajectories – Charles François Sturm
- Suess effect – Hans Eduard Suess
- Sunyaev–Zel'dovich effect – Rashid Sunyaev and Yakov Zel'dovich
- Syracuse problem – see Collatz conjecture, above
Read more about this topic: Scientific Phenomena Named After People