‎Physique‎

‎"SCHRÖDINGER, ERWIN.‎

‎Isotopie und Gibbssches Paradoxen.‎

‎Braunschweig und Berlin, Vieweg & Sohn, Julius Springer, 1921. 8vo. Bound in contemporary half cloth. Stamp to front free end paper. In ""Zeitschrift für Physik. Hrasg. von Karl Scheel"", vol. 5. Entire volume offered. [Schrödinger's paper:] pp. 163-66. [Entire volume: IV, 449, (1) pp].‎

‎First apperance of Schrödinger's paper on isotopy and the Gibb's paradox. ""Schrödinger started explicitly from the previous discussion between de Hevesy and Paneth on the one hand, and Fajans on the other, summarizing the results as 'Thermodynamical diversity of isotopes in principle, in spite of their complete or nearly complete chemical replaceability'. Thus far he partially supported the view promoted by Karlsruhe physico-chemist. However, he contradicted a result which Fajans had obtained, stating that the energy set free by mixing or diffusion of the volumes, containing different isotopes of the same chemical element, was proportional to the difference of the respective atomic weights - hence a consequence, it should become arbitrarily small as the mass difference disappeared. (Mehra, The Historical Development of Quantum Theory, P. 340).‎

Referenz des Buchhändlers : 48926

‎"SCHRÖDINGER, ERWIN.‎

‎Science and the Human temperament. Translated and with a biographical Introduction by James Murphy. Foreword by Lord Rutherford.‎

‎London, George Allen & Unwin, (1935). Orig. full cloth. 154 pp. + Publisher's announcements.‎

‎First edition. 2 of the seven papers were published before in 1932 in German as ""Zwei Vorträge"". In 1933 Schrödinger was awarded the Nobel prize jointly with Dirac.‎

Referenz des Buchhändlers : 31678

‎"SCHRÖDINGER, ERWIN.‎

‎Theorie der Pigmente von größter Leuchtkraft‎

‎Leipzig, Ambrosius Barth, 1920. 8vo. In full black cloth with gilt lettering to spine. In ""Annalen der Physik"", bd. 62. Entire volume offered. Small library stamp to lower part of title page and library label pasted on to front free end papers. Fine and clean. Pp. 603-22. [Entire volume: VI. 762 pp.].‎

‎First appearance of Schrödinger's important paper in which he presented his theory of pigments with highest luminosity""His first papers on relativity pointed to a second major field of interest. In addition to these works, and his early papers on relativity, Schrödinger made a detailed study, through both measurement and computation, of the metric of color space and the theory of color vision."" (DSB).‎

Referenz des Buchhändlers : 50598

‎"SCHRÖDINGER, ERWIN.‎

‎Über den Comptoneffekt (+) Der Energieimpulssatz der Materiewellen.‎

‎Leipzig, Ambrosius Barth, 1927. 8vo. In contemporary full cloth with gilt lettering to spine. In ""Annalen der Physik"", Band 82. Entire volume offered. Library stamp to pasted down front and back free end-paper. Embossed stamp on title page. A fine and clean copy. Pp. 257-64"" Pp. 265-73. [Entire volume: VIII, 1168 pp. + 14 plates.‎

‎First appearance of Schrödinger's famous treatment of the Compton effect.""Schrödinger approached the wave mechanical treatment of the Compton effect in his own paper [the present] on a far less technical level [than Gordon]. He practically went back to the optical analogies that had stimulated the whole development in November 1925, and in which the properties of microscopic particles were described by matter waves and their propagation in homogeneous media. From such consideration, he now - a year later - drew the following conclusion: ""It is to be expected, nay, even demanded, that we should be able, by means of quite simple phase considerations…, to explain the connection between the changes in direction and frequency of the ether wave which occur in the Compton effect and the change of velocity of the electron."" (Mehra, The Historical Development of Quantum Theory)""Compton was able to account for this (lenghtening of wavelenght) by presuming that a photon of light struch an electron, which recoiled, subtracting some energy from the photon and therefore increasing its wavelenght. This made it seem that a photon acted as a particle: thus after more than a century, the particulate natuer of light, as evolved by Newton, was revived... What itamounted to was that Compton brought to fruition the view that electromagnetic radiation had both a wave aspect and a particle aspect, and that the aspect which was most evident depended on how the radiation was tested. De Broglie was, at the same time, showing that this held true also for ordinary particles, such as electrons."" (Asimov)‎

Referenz des Buchhändlers : 50596

‎"SCHRÖDINGER, ERWIN.‎

‎Über den Comptoneffekt (+) Der Energieimpulssatz der Materiewellen.‎

‎Leipzig, Ambrosius Barth, 1927. 8vo. In contemporary full cloth with gilt lettering to spine. In ""Annalen der Physik"", Band 82. Entire volume offered. Library stamp to pasted down front and back free end-paper. Embossed stamp on title page. A fine and clean copy. Pp. 257-64" " Pp. 265-73. [Entire volume: VIII, 1168 pp. + 14 plates.‎

‎"SCHRÖDINGER, ERWIN.‎

‎Über die Kohärenz in Weitgeöffneten Bündeln.‎

‎Leipzig, Ambrosius Barth, 1920. 8vo. In contemporary full cloth with gilt lettering to spine. In ""Annalen der Physik"", Vierte Folge, Band 61. Entire volume offered. Library labels pasted on the pasted down front free end paper. Stamp to title page and repairs to first leaf (not affecting text), otherwise a fine copy. Pp. 69-86. [Entire volume: 760, VIII pp.].‎

‎First appearance of Schrödinger's paper concerning the coherence of wide open bundles.‎

Referenz des Buchhändlers : 50322

‎"SCHRÖDINGER, ERWIN.‎

‎Über die Rotationswärme des Wasserstoffs.‎

‎Berlin, Julius Springer, 1924. 8vo. Bound in contemporary halfcloth. In ""Zeitschrift für Physik"", Bd. 30.Entire issue offered. Stamp to front free end paper. Fine and clean. Pp. 341-359. [Entire volume: IV, 387 pp].‎

‎First printing of Schrödinger's paper on hydrogen heat.‎

Referenz des Buchhändlers : 48983

‎"SCHRÖDINGER, ERWIN.‎

‎Über die Rotationswärme des Wasserstoffs.‎

‎Berlin, Julius Springer, 1924. 8vo. Bound in contemporary halfcloth. In ""Zeitschrift für Physik"", Bd. 30.Entire issue offered. Stamp to front free end paper. Fine and clean. Pp. 341-359. [Entire volume: IV, 387 pp].‎

‎"SCHRÖDINGER, ERWIN.‎

‎Über die spezifische Wärme fester Körper bei hoher Temperatur und über die Quantelung von Schwingungen endlicher Amplitude.‎

‎(Berlin, Julius Springer, 1922). 8vo. Bound in contemporary half cloth. In: ""Zeitschrift für Physik"", 11 band, 1922 (not the complete issue). Find and clean. Pp. 170-76. [Offered volume: Pp. 1-324, 327-398.]‎

‎First printing.‎

Referenz des Buchhändlers : 47377

‎"SCHRÖDINGER, ERWIN.‎

‎Über die spezifische Wärme fester Körper bei hoher Temperatur und über die Quantelung von Schwingungen endlicher Amplitude.‎

‎(Berlin, Julius Springer, 1922). 8vo. Bound in contemporary half cloth. In: ""Zeitschrift für Physik"", 11 band, 1922 (not the complete issue). Find and clean. Pp. 170-76. [Offered volume: Pp. 1-324, 327-398.]‎

‎"SCHRÖDINGER, ERWIN. - FIRST TREATMENT OF WAVE MECHANICS IN ENGLISH.‎

‎An undulatory Theory of the Mechanics of Atoms and Molecules.‎

‎Minneapolis, Minn., The Physicalreview, 1926. 4to. Contemp. full buckram. Small tear to first hinge at foot. A stamp in upper right corner on titlepage and 2 other pages. In: ""The Physical Review. Conducted by the American Physical Society"", Vol. 28, Second Series. VI,1343 pp. (Entire volume offered).Schrödinger's paper: pp. 1049-1070. Internally clean and fine.‎

‎"SCHWERD, F. M.‎

‎Die Beugungserscheinungen aus den Fundamentalgesetzen der Undulationstheorie. Analytisch entwickelt und in Bildern dargestellt. Mit 18 zum Teil illuminirten Tafeln. - [ANTICIPATING THE DISCOVERY OF X-RAYS]‎

‎Mannheim, Schwan und Goetz, 1835. 4to. Contemporary halfcalf with marbled paper over boards. Half-title page supplied in facsimile. Library stamp and library-markings in old hand to title-page. XII (lacking the half-title, being pp. (I-II)) , 143, (8, -tables + errata) pp + 18 folded plates, two of which are hand-coloured. Spine and corners with wear. Internally some lighter brownspotting.‎

‎"SENARMONT, HENRI HUREAU DE. - CRYSTALLOGRAPHY.‎

‎Mémoire sur les modifications que la réflexion spéculaire à la surface des corps métalliques imprime à un rayon de lumière polarisée.‎

‎(Paris, Fortin, Masson et Cie, 1840). 8vo. Without wrappers. Disbound. In: 'Annales de Chimie et de Physique', 2e Series, tome 73, Cahier 4. Pp. 337-446 a. 1 plate. (entire issue offered). Senarmont's paper: pp. 337-362. Some scattered brownspots.‎

‎"SHANNON, C. E.‎

‎Prediction and Entropy of Printed English. (Contained in The Bell System Technical Journal, Volume XXX, No. 1, p.50-64.). - [FIRST MEASUREMENTS OF ""SHANNON ENTROPY"".]‎

‎(New York, American Telephone and Telegraph Company, 1951). 8vo. The complete issue in original blue printed wrappers. Pp. 50-64. [Entire volume: pp. 1-212.].‎

‎"SHANNON, CLAUDE E.‎

‎Memory Requirements in a Telephone Exchange (Manuscript Received Dec. 7, 1949).‎

‎(New York), American Telephone and Telegraph Company, 1950. 8vo. In the original printed blue wrappers. In Volume XXIX, July, No. 3, 1950 of ""The Bell System Technical Journal"". A bit of minor marginal browning to extremities, otherwise fine and clean. Pp. 343-359. [Entire issue: Pp. 295-468].‎

‎First edition of Shannon's influential paper on how to construct a telephone exchange network. ""The problem of designing a good rearrangeable network was (probably first) considered in a paper of C. E. Shannon investigating memory requirements in a telephone exchange. On the networks that he considered he imposed the realistic ""separate memory condition"" to the effect that in operation a separate part of the memory can be signed to each call on progress. This means that completion of a new call or termination of an old call will not disturb the state of memory elements associated with any call in progress. [...] Shannon's separate memory condition is actually met by modern connecting networks [...]. (Benes, Vaclav Edward. Mathematical Theory of Connecting Networks and Telephone Traffic: 017, 1965, p. 119.) Claude Shannon is widely regarded as being the father of information theory and cryptography. Origins of Cyberspace 883.The present issue also includes:1. Southworth, George C. Principles and Applications of Waveguide Transmission. Pp. 295-342.2. Hartley, R.V.L. Matter, A Mode of Motion. Pp. 350-368.3. Hartley, R.V.L. The Reflection of Diverging Waves by a Gyrostatic Medium. Pp. 369-389.4. Pierce, J.R. Traveling-Wave Tubes (Third Installment). Pp. 390-460.‎

Referenz des Buchhändlers : 62913

‎"SHANNON, CLAUDE E.‎

‎Probability of Error for Optimal Codes in a Gaussian Channel. [Manuscript received October 17, 1958].‎

‎New York, American Telephone and Telegraph Company, 1959. 8vo. Volume XXXVIII, 1959 of The Bell System Technical Journal bound in a nice full green cloth with gilt title to spine. Library stamp to top of title page. Binding tight, clean and fresh. Also internally very nice and clean. Pp. 611-656. [Entire volume: 14, (2), 907 pp.]‎

‎First edition.From the introduction to the present article: ""A study is made of coding and decoding systems for a continuous channel with an additive Gaussian noise and subject to an average power limitation at the transmitter. Upper and lower bounds are found for the error probability in decoding with optimal codes and decoding systems. These bounds are close together for signaling rates near channel capacity and also for signaling rates near zero, but diverge between. Curves exhibiting these bounds are given."" Claude Shannon is widely regarded as being the father of information theory and cryptography.See:OOC 898.‎

Referenz des Buchhändlers : 42742

‎"SHAPIRO, ASCHER.‎

‎Bath-Tub Vortex. - [THE CORIOLIS EFFECT ON A BATHTUB VORTEX]‎

‎London, Macmillian, 1962. Royal8vo. Bound in contemporary full cloth with two black title label to spine. In ""Nature"", Vol. 196, October - December. Library labels to end paper and one library stamp to title page. Light soiling to extremities, internally fine and clean. Pp. 1080-1. [Entire colume: LII, 1346 pp.].‎

‎First appearance of Shapiro's famous paper in which he sought to describe a bathtub vortex with the Coriolis Effect. This eventually gave birth to the urban myth that a toilet vortex always will have a counter clockwise flow in the Northern Hemisphere. The Coriolis effect on a micro level is still disputed and has never been satisfyingly confirmed or rejected. Scientists were aware that Earth's rotation alters the trajectory of objects in motion. This phenomenon causes low-pressure weather systems to twist counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The Coriolis effect, as it's known, had long been well documented as the cause of hurricanes and tornadoes. But despite previous attempts, no one had shown that the effect-first described in 1835 by the French engineer and mathematician Gustave-Gaspard Coriolis-works on very small scales as well. Though in theory it should influence bathwater's exit through a drain, the Coriolis effect was thought to be too small to see.""For his experiment, Shapiro used a circular, flat-bottomed tub with a centered drain hole three-eighths of an inch in diameter to which he attached a 20-foot length of hose, plugged with a stopper at the end. He filled the tank six inches deep with clean, room-temperature water. Small variations-air movement, a temperature change, a surface disturbance-create buoyancy currents that overshadow the Coriolis effect. So Shapiro did much tinkering to cancel out these possible sources of interference-covering the tank with a sheet of plastic to keep out air currents, for example, and carefully controlling the room's temperature. He also filled the tank by swirling water in clockwise, so that if the water drained counterclockwise, the direction would not have been influenced by how the tank was filled.After 24 hours of letting the water settle, Shapiro carefully pulled the plug from the end of the hose, gently placing above the drain a small float made of two crossed slivers of wood an inch long. It took about 20 minutes for the tub to drain completely. For the first 12 to 15 minutes, the float remained motionless. Then it began to rotate almost imperceptibly, counterclockwise, reaching a peak speed of approximately one revolution every three to four seconds. Proving that the Coriolis effect can be detected in a bathtub-size tank, albeit under carefully controlled conditions, was a remarkable achievement. At MIT's latitude of 42°, the effect was ""only thirty-millionths that of gravity, which is so small that it will be overcome by filling and even temperature differences and water impurities,"" reported one of many newspapers and periodicals covering the experiment. Shapiro's results were published in Nature and verified by colleagues who used his technique to demonstrate a clockwise flow in the Southern Hemisphere. The findings fascinated a curious public of all ages. Shapiro would also become known for explaining and improving the aerodynamics of golf ball dimples, as well as for helping to develop the intra-aortic balloon for heart patients and devices to treat blood clots, asthma, emphysema, and glaucoma. But for more than a decade after the bathtub test, he would receive letters and newspaper clippings from all over the world about what was dubbed the ""bathtub vortex"" controversy. "" (MIT Technology Review).‎

Referenz des Buchhändlers : 49162

‎"SHEWHART, W.A. & D. SLEPIAN.‎

‎Nature and Origin of Standards of Quality [Shewhart] (+) Fluctuations of Random Noise Power [Slepian]. - [THE FATHER OF QUALITY CONTROL]‎

‎(New York), American Telephone and Telegraph Company, 1958. 8vo. Volume XXXVII, January, No. 1, 1958 of ""The Bell System Technical Journal"". In the original printed blue wrappers. A bit of sunning to spine and previous owner's signature to front wrapper, otherwise a very nice and fresh copy. [Shewhart's paper:] Pp. 1-22. [Slepian's paper:] Pp. 163-184.‎

‎First edition of Shewhart's important paper on statistical quality control.""Shewhart successfully brought together the disciplines of statistics, engineering, and economics and became known as the father of modern quality control. Shewhart was concerned that statistical theory serve the needs of industry. He exhibited the restlessness of one looking for a better way. A man of science who patiently developed and tested his ideas and the ideas of others, he was an astute observer of developments in the world of science and technology. In that respect, the field of quality control can claim a genuine pioneer in Shewhart."" (Berger, Roger W. The Certified quality engineer handbook, 2002, P. 55).Most of Shewhart's papers were keept unpublished but implemented in the Bell Laboratories. The present paper was written in 1935 and it's techniques were put into practice immediately after it was, however, first published for a wider audience with the present article in 1958.The issue also includes the first edition of SLEPIAN'S groundbreaking paper on fluctuations of random noise. His analysis has exercised influence in measuring and analyzing back ground noise from space and, more exotic, analysis signals from outer space in search for extra-terrestrial aliens. The following articles of interest are also contained in the present volume:1. Levenbach, G.J. Contribution of Statistics to the Development Program of a Transformer for L3 Carrier System. Pp. 23-54.2. Olmstead, Paul S. Runs Determined in a Sample by an Arbitrary Cut. Pp. 55-82. 3. Roberts, S.W. Properties of Control Chart Zone Tests. Pp. 83-114.4. Murphy, R.B. Criterion to Limit Inspection Effort in Continuous Sampling Plans. Pp. 115-134.5. Sobel, Milton" Huyett, Marilyn J. Nonparametric Definition of the Representativeness of a Sample - with Tables. Pp. 135-161.6. Blackman, R.B. Tukey, J.W. The Measurement of Power Spectra from the Point of View of Communications Engineering - Part I. Pp. 185-282.‎

Referenz des Buchhändlers : 43388

‎"SHOCKLEY, W.‎

‎The Quantum Physics of Solids, I. The Energies of Electrons in Crystals. - [PHYSICS NOBEL PRIZE 1956 - THE FATHER OF SILICON VALLEY.]‎

‎New York, American Telephone and Telegraph Company, 1939. 8vo. Original full blue cloth. The entire volume XVIII, 1939 of The Bell System Technical Journal. Library stamp to free front end-paper. Binding tight and clean. Also internally very nice and clean. Pp. 645-724. [Entire volume: (8), 748 pp.].‎

‎First edition of the first paper of a series of three on the quantum physics of solids by the Nobel Prize winner in Physics William Shockley.""It is proposed to make this paper the first of a series of three dealing with the quantum physics of solids"" (From the introduction to the present article). William Shockley was co-Inventor of the Transistor which awarded him the Nobel Prize in 1956. His attempts to commercialize the transistor in the 1950s and 1960s led to California's ""Silicon Valley"" becoming a hub of electronics innovation.‎

Referenz des Buchhändlers : 42966

‎"SHOCKLEY, W. (+) W.T. READ.‎

‎Dislocation Models of Crystal Grain Boundaries - [THE SHOCKLEY PARTIAL DISLOCATION]‎

‎Lancaster, American Physical Society, 1950. Lex8vo. Entire volume offered in the original blue wrappers with previous owner´s stamps. In ""The Physical Review"" Volume 78, May 1, No. 3, 1950 of , Second Series. A fine and clean copy. Pp. 275-290. [Entire volume: Pp. 189-357].‎

‎First printing of the classical paper in which the The Shockley Partial Dislocation was described for the first time.‎

Referenz des Buchhändlers : 46569

‎"SIEMENS, CHARLES WILLIAM [+] HENRY CHARLES FORDE.‎

‎The Malta and Alexandria Telegraph: Comprising of the following papers, [Forde:] I: The Malta and Alexandria Submarine Telegraph Cable. [Siemens:] II: On the Electricfal Tests. - [THE MALTA-ALEXANDRIA CABLE]‎

‎London, William CLowes and Sons, 1863. 8vo. In the original printed wrappers with Siemens's inscription to front wrapper: ""to Mr. A. L. Ternant / from Author"". With previous owner's stamp to lower part of front wrapper: ""A. L. Ternant"". Lacking upper part of spine, a few marginal annotations in pencil throughout. 50, (5) pp. + 3 large folded plates.‎

‎First printing of this important publication in the history of telegraphs cables with a most interesting presentation inscription: It was given by Siemens to A. L. Ternant, author to several early paper on submarine cables. The Malta-Alexandria cable was ordered by the British government, manufactured by John Pender, and constitute one of the very first submarine telegraph cables. ""The making and laying of the Malta to Alexandria cable gave rise to researches on the resistance and electrification of insulating materials under pressure, which formed the subject of a paper read before the British association in 1863. The effect of pressure up to 300 atmospheres was observed, and the fact elicited that the inductive capacity of gutta-percha is not affected by increased pressure, whereas that of india-rubber is diminished. The electrical tests employed during the construction of the Malta and Alexandria cable, and the insulation and protection of submarine cables, also formed the subject of a paper [the present]."" (Munro, Heros of the Telegraph, P. 72). The Malta-Alexandria cable was the first Siemens was involved in and the experience made him in 1874: ""design the cable ship Faraday and assisted in the laying of the first of several transatlantic cables that it completed. During the last fifteen years of his life he actively supported the development of the engineering profession and its societies and stimulated public interest in the conservation of fuel, the reduction of air pollution and the potential value of electric power in a wide variety of engineering applications.(DSB).In 1859 Glass, Elliot and Company received an order from the British Government to manufacture and lay a cable from Falmouth, England to Gibraltar. The government then changed the route to Rangoon - Singapore and finally to Malta - Alexandria, Egypt.‎

Referenz des Buchhändlers : 48490

‎"SIEMENS, WILLIAM.‎

‎The Electro-Magnetic Practical System of Units. - [WITH AUTHOR'S PRESENTATION INSCRIPTION]‎

‎London, William Clowes and Sons, 1882. 8vo. In the original printed sown wrappers. With author's inscription to top of front wrapper: ""from the Author"". A few occassional brown spots. Has been bended vertically. Otherwise a fine copy. 7 pp.‎

‎First printing, with author's presentation inscription, of Siemens' proposal to create an universal unit of measurement of resistance. ""Siemens' outstanding contribution to scientific technology was his discovery of the dynamo principle, announced to the Berlin Academy of Sciences in January 1867. Having already introduced the double-T armature, the electromagnetic field, and the external load of an electrical generator in a single circuit, thereby avoiding the costly permanent magnets previously used in the field. Other inventors and scientists discovered the dynamo principle at about the same time"" but Siemens foresaw the consequences of his ""dynamo"" for heavy-current, or power, uses and developed practical applications. His company pioneered in using electricity for streetcars and mine locomotives, in electrolysis, and in central generating stations."" (DSB)‎

Referenz des Buchhändlers : 48170

‎"SILBERSTEIN, L.‎

‎Nachtrag zur Abhandlung über ""Elektromagnetische Grundgleichungen in bivectorieller Behandlung"". - [THE RIEMANN-SILBERSTEIN VECTOR]‎

‎Leipzig, Ambrosius Barth, 1907. 8vo. In full cloth with gilt lettering to spine. In ""Annalen der Physik"", Vierte Folge, Band 24. Entire volume offered. Library labels pasted on the pasted down front free end paper. Traces after a label to lower part of spine. Stamp to title page. Internally fine and clean. Pp. 783-4. [Entire volume: 968, VIII pp.].‎

‎First printing of Silberstein's important paper in which he presented what was later to be known as the Riemann-Silberstein vector: a complex vector that combines the electric field E and the magnetic field B.‎

Referenz des Buchhändlers : 50327

‎"SMITH, ROBERT. - THE MAIN TEXTBOOK ON OPTICS IN THE 18TH CENTURY.‎

‎Vollständiger Lehrbegriff der Optik nach Herrn Robert Smiths Englischen mit Aenderungen und Zusätzen ausgearbeitet von Abraham Gotthelf Kästner.‎

‎Altenburg, Richterischen Buchhandlung, 1755. 4to. Contemp. boards. Handwritten titlelabel on spine. Engraved titlevignette. (20),531,(5) pp. and 22 folded engraved plates. A few scattered brownspots, but in general clean.‎

‎"SMOLUCHOWSKI, MARIAN von. - BROWNIAN MOVEMENTS‎

‎Zur kinetischen Theorie der Brownschen Molekularbewegung und der Suspensionen. (Bearbeitet nach einer am 9. Juli 1906 der Krakauer Akademie vorgelegten und demnächst in dem Bullet. Int. Crac. erschienenen Abhandlung).‎

‎(Leipzig, Barth, 1906). Without wrappers.. In: ""Annalen der Physik. Vierte Folge. Bd. 21, No. 14.. Pp. 509-780. (Entire issue offered No 14). Smoluchowski's paper: pp. 756-780. Clean and fine.‎