Certain ancient stringed instruments were played with a plectrum or plucker made of the quill of a bird's feather, and the word has thus been used of a plectrum made of other material and differing in shape, and also of an analogous object for striking the strings in the harpsichord, spinet or virginal.
For the investigation of the spectra of gases at reduced pressures the so-called Plucker tubes (more generally but incorrectly called Geissler tubes) are in common use.
When, for instance, we observe the relation of the gas contained in a Plucker tube through which an electric discharge is passing, there can be little doubt that the partition of energy is very different from what it would be in thermal equilibrium.
(b) If a spark be sent through a Plucker tube containing hydrogen the lines are widened when the pressure 1 Trans.
According to circumstances, the colour of the light obtained from a Plucker vacuum tube changes "from red to a rich steel blue," to use the words of Crookes, who first described the phenomenon.
Plucker and his disciple J.
The particular details of the phenomena observed will be found described in the article Electric conduction (§ The main fact discovered by researches of Plucker, Hittorf and Crookes was that in a vacuum tube containing extremely rarefied air or other gas, a luminous discharge takes place from the negative electrode which proceeds in lines normal to the surface of the negative electrode and renders phosphorescent both the glass envelope and other objects placed in the vacuum tube when it falls upon them.
JULIUS PLUCKER (r801-1868), German mathematician and physicist, was born at Elberfeld on the 16th of June r 801.
The title of his "habilitationsschrift," Generalem analyseos applicationem ad ea quae geometriae altioris et mechanicae basis et fundaments sunt e serie Tayloria deducit Julius Plucker (Bonn, 1824), indicated the course of his future researches.
Plucker aimed at furnishing modern geometry with suitable analytical methods so as to give it an independent analytical development.
Another subject of importance which Plucker took up in the Entwickelungen was the curious paradox noticed by L.
Plucker finally (Gergonne Ann., 1828-1829) showed how many points must be taken on a curve of any degree so that curves of the same degree (infinite in number) may be drawn through them, and proved that all the points, beyond the given ones, in which these curves intersect the given one are fixed by the original choice.
In 1833 Plucker left Bonn for Berlin, where he occupied a post in the Friedrich Wilhelm's Gymnasium.
In 1836 Plucker returned to Bonn as ordinary professor of mathematics.
Plucker, first by himself and afterwards in conjunction with W.
Hittorf tells us that Plucker never attained great manual dexterity as an experimenter.
Induced by the encouragement of his mathematical friends in England, Plucker in 1865 returned to the field in which he first became famous, and adorned it by one more great achievement - the invention of what is now called "line geometry."
Plucker himself worked out the theory of complexes of the first and second order, introducing in his investigation of the latter the famous complex surfaces of which he caused those models to be constructed which are now so well known to the student of the higher mathematics.
Among the very numerous honours bestowed on Plucker by the various scientific societies of Europe was the Copley medal, awarded to him by the Royal Society two years before his death.
We now come to Julius Plucker; his " six equations " were given in a short memoir in Crelle (1842) preceding his great work, the Theorie der algebraischen Curven (1844).
Plucker first gave a scientific dual definition of a curve, viz.; " A curve is a locus generated by a point, and enveloped by a line - the point moving continuously along the line, while the line rotates continuously about the point "; the point is a point (ineunt.) of the curve, the line is a tangent of the curve.
Plucker, moreover, imagined a system of line-co-ordinates (tangential co-ordinates).
The expression for the number of inflections 3m(rn - 2) for a curve of the order m was obtained analytically by Plucker, but the theory was first given in a complete form by Hesse in the two papers " Uber die Elimination, u.s.w.," and " Uber die Wendepuncte der Curven dritter Ordnung " (Crelle, t.
The expression 2m(m - 2) (m - 9) for the number of double tangents of a curve of the order in was obtained by Plucker only as a consequence of his first, second, fourth and fifth equations.
Investigations in regard to them are given by Plucker in the Theorie der algebraischen,Curven, and in two memoirs by Hesse and Jacob Steiner (Crelle, t.
It was assumed by Plucker that the number of real double tangents might be 28, 16, 8, 4 or o, but Zeuthen has found that the last case does not exist.
The points called foci presented themselves in the theory of the conic, and were well known to the Greek geometers, but the general notion of a focus was first established by Plucker (in the memoir " Uber solche Puncte die bei Curven einer hdheren Ordnung den Brennpuncten der Kegelschnitte entsprechen " (Crelle, t.