A solenoid (/ˈsoʊ.lə.nɔɪd/)1 (from the French solénoïde, derived in turn from the Greek solen "pipe, channel" + combining form of Greek eidos "form, shape") is a coil wound into a tightly packed helix. The term was invented by French physicist André-Marie Ampère to designate a helical coil.
In physics, the term refers to a coil whose length is substantially greater than its diameter, often wrapped around a metallic core, which produces a uniform magnetic field in a volume of space (where some experiment might be carried out) when an electric current is passed through it. A solenoid is a type of electromagnet when the purpose is to generate a controlled magnetic field. If the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet. Not all electromagnets and inductors are solenoids; for example, the first electromagnet, invented in 1824, had a horseshoe rather than a cylindrical solenoid shape.
In engineering, the term may also refer to a variety of transducer devices that convert energy into linear motion. The term is also often used to refer to a solenoid valve, which is an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve, or a solenoid switch, which is a specific type of relay that internally uses an electromechanical solenoid to operate an electrical switch; for example, an automobile starter solenoid, or a linear solenoid, which is an electromechanical solenoid. Solenoid bolts, a type of electronic-mechanical locking mechanism, also exist. Wikipedia, Solenoid
A common tractive electromagnet is a uniformly-wound solenoid and plunger. The solenoid is a coil of wire, and the plunger is made of a material such as soft iron. Applying a current to the solenoid applies a force to the plunger and may make it move. The plunger stops moving when the forces upon it are balanced. For example, the forces are balanced when the plunger is centered in the solenoid. The maximum uniform pull happens when one end of the plunger is at the middle of the solenoid. Wikipedia, Solenoid
"Future laboratory techniques should eliminate from two thirds to nine tenths of its wiring. This will follow a greater knowledge of the geometry and mathematics of space, and especially the tonal nature of octave waves, to make it possible for cathodes to find their anodes without wires, as they do in Nature. The cylindrical solenoids of today should be entirely eliminated, especially where they encase anodes and prevent their expression of power by the way of equators." [Atomic Suicide, page 184]
"It is not well, however, to leave this mystery of how "magnetism" picks up iron nails and "attracts" steel needles, unexplained, for the entire electrical engineering world is paying heavily for lack of this understanding in many ways, the more expensive one being the vast wastage caused by building improper coils, solenoids, armatures, step-up, step-down transformers and electronic tubes." [Atomic Suicide, page 185]
"It is a commonly known fact by every physicist and laboratory worker that electricity runs only in the direction of the turnings in a solenoid coil. Every such worker is also perfectly familiar with the effect of polarization which evidences its effect at 90 degrees from the direction - and plane - of the electric current. These two seeming directions, and effects, are confusing to him for the idea of polarization, as an extension of stillness, has not yet entered his thinking." [Atomic Suicide, page 283-284]
angles of 90 degrees
Figure 5.7 - Vortices on Three Planes 90 Degrees to Each Other
Light Rings formed at 90 Degrees to Magnetic Center Line
plane of 90 degrees