Guide to the use of this subsection (classes ) The following notes are meant to assist in the use of this part of the classification scheme. In this subsection, subclasses or groups designating "engines" or "pumps" cover methods of operating the same, unless otherwise specifically provided for. In this subsection, the following terms or expressions are used with the meanings indicated: "engine" means a device for continuously converting fluid energy into mechanical power. Thus, this term includes, for example, steam piston engines or steam turbines, per se, or internal-combustion piston engines, but it excludes single-stroke devices. "Engine" also includes the fluid-motive portion of a meter unless such portion is particularly adapted for use in a meter; "pump" means a device for continuously raising, forcing, compressing, or exhausting fluid by mechanical or other means. Thus, this term includes fans or blowers; "machine" means a device which could equally be an engine and a pump, and not a device which is restricted to an engine or one which is restricted to a pump; "positive displacement" means the way the energy of a working fluid is transformed into mechanical energy, in which variations of volume created by the working fluid in a working chamber produce equivalent displacements of the mechanical member transmitting the energy, the dynamic effect of the fluid being of minor importance, and vice versa; "non-positive displacement" means the way the energy of a working fluid is transformed into mechanical energy, by transformation of the energy of the working fluid into kinetic energy, and vice versa; "oscillating-piston machine" means a positive-displacement machine in which a fluid-engaging work-transmitting member oscillates. This definition applies also to engines and pumps; "rotary-piston machine" means a positive-displacement machine in which a fluid-engaging work-transmitting member rotates about a fixed axis or about an axis moving along a circular or similar orbit. This definition applies also to engines and pumps; "rotary piston" means the work-transmitting member of a rotary-piston machine and may be of any suitable form, e.g., like a toothed gear; "cooperating members" means the "oscillating piston" or "rotary piston" and another member, e.g., the working-chamber wall, which assists in the driving or pumping action; "movement of the co-operating members" is to be interpreted as relative, so that one of the "co-operating members" may be stationary, even though reference may be made to its rotational axis, or both may move; "teeth or tooth equivalents" include lobes, projections or abutments; "internal-axis type" means that the rotational axes of the inner and outer co-operating members remain at all times within the outer member, e.g., in a similar manner to that of a pinion meshing with the internal teeth of a ring gear; "free piston" means a piston of which the length of stroke is not defined by any member driven thereby; "cylinders" means positive-displacement working chambers in general. Thus, this term is not restricted to cylinders of circular cross-section; "main shaft" means the shaft which converts reciprocating piston motion into rotary motion or vice versa; "plant" means an engine together with such additional apparatus as is necessary to run the engine. For example, a steam engine plant includes a steam engine and means for generating the steam; "working fluid" means the driven fluid in a pump and the driving fluid in an engine. The working fluid may be in a gaseous state, i.e., compressible, or liquid. In the former case coexistence of two states is possible; "steam" includes condensable vapours in general, and "special vapour" is used when steam is excluded; "reaction type" as applied to non-positive-displacement machines or engines means machines or engines in which pressure/velocity transformation takes place wholly or partly in the rotor. Machines or engines with no, or only slight, pressure/velocity transformation in the rotor are called "impulse type". In this subsection: cyclically operating valves, lubricating, gas-flow silencers or exhaust apparatus, or cooling are classified in subclasses , , , irrespective of their stated application, unless their classifying features are peculiar to their application, in which case they are classified only in the relevant subclass of classes ; lubricating, gas-flow silencers or exhaust apparatus, or cooling of machines or engines are classified in subclasses , , except for those peculiar to steam engines which are classified in subclass . For use of this subsection with a good understanding, it is essential to remember, so far as subclasses , , , , and , , , which form its skeleton, are concerned: the principle which resides in their elaboration, the classifying characteristics which they call for, and their complementarity. Principle This concerns essentially the subclasses listed above. Other subclasses, notably those of class , which cover better-defined matter, are not considered here. Each subclass covers fundamentally a genus of apparatus (engine or pump) and by extension covers equally "machines" of the same kind. Two different subjects, one having a more general character than the other, are thus covered by the same subclass. Subclasses , , , beyond the two subjects which they cover, have further a character of generality in relation to other subclasses concerning the different species of apparatus in the genus concerned. This generality applies as well for the two subjects dealt with, without these always being in relation to the same subclasses. Thus, subclass , in its part dealing with "machines", should be considered as being the general class relating to subclasses , , and in its part dealing with "engines" as being general in relation to subclass . Characteristics The principal classifying characteristic of the subclass is that of genera of apparatus, of which there are three possible: Machines; engines; pumps. As stated above, "machines" are always associated with one of the other two genera. These main genera are subdivided according to the general principles of operation of the apparatus: Positive displacement; non-positive displacement. The positive displacement apparatus are further subdivided according to the ways of putting into effect the principle of operation, that is, to the kind of apparatus: Simple reciprocating piston; rotary or oscillating piston; other kind. Another classifying characteristic is that of the working fluid, in respect of which three kinds of apparatus are possible, namely: Liquid and elastic fluid; elastic fluid; liquid. Complementarity This resides in association of pairs of the subclasses listed above, according to the characteristics under consideration in respect of kind of apparatus or working fluid. The subclasses concerned with the various principles, characteristics and complementarity are shown in the subsection index below. It is seen from this index that: For the same kind of apparatus in a given genus, the characteristics of "working fluid" associates: and to Machines and to Machines and to Machines and to Engines and to Engines and to Engines For the same kind of working fluid, the "apparatus" characteristic relates subclasses in the same way as considerations of relative generality. MACHINES positive displacement rotary or oscillating piston liquid and elastic fluid or elastic fluid liquid only reciprocating piston or other liquid and elastic fluid or elastic fluid liquid only non-positive displacement liquid and elastic fluid or elastic fluid liquid only ENGINES positive displacement rotary or oscillating piston liquid and elastic fluid or elastic fluid liquid only reciprocating piston or other liquid and elastic fluid or elastic fluid liquid only non-positive displacement liquid and elastic fluid or elastic fluid liquid only PUMPS positive displacement rotary or oscillating piston reciprocating piston or other non-positive displacement Combinations of positive-displacement and non-positive-displacement pumps are classified in subclass as a general subclass for pumps, and in subclasses , in respect of matter specific to those subclasses. If the disclosure gives no indication as to whether it relates to electrical means or not, it should be classified as if it were in fact electric. Attention is drawn to Note III following the Contents of Section of section H. Attention is drawn to the following places: Lights for cultivation in receptacles, forcing frames, greenhouses Aquaria Fishing nets Fishing baits Catching insects Baker's ovens Sticks Bags, purses, or the like Toilet or cosmetic powder containers Shaving mirrors Shop windows or showcases Suction cleaners Medical instruments for examining body cavities or tubes Curing dental plastics prostheses by light action Massage adapted for simultaneous treatment with light Radiation therapy Clubs Balls Roller skates or skate boards Tops Toy vehicles Model railways Spanners, wrenches, screwdrivers Hair clippers or dry shavers Accessories for razors Photographic composing machines Typewriters or selective printing machines Writing implements Lamps for baking lacquers used in painting or artistic drawing Arrangement of signalling or lighting devices, the mounting or supporting thereof or circuits therefor, for vehicles in general Railway vehicles Railway light signals Points, form signals, or gates Cycles Ships Life-buoys, life-belts, lifejackets Aircraft Apparatus for transferring liquids Sewing machines Road signs Road surface markings Tents or canopies Locks or keys Air conditioning systems Outlets for directing air into rooms or spaces combined with lighting fixtures Cooling or freezing apparatus Furnaces, kilns, ovens or retorts Night sights Levels Compasses Measuring arrangements Weighing apparatus Thermometers Speedometers Instruments for measuring Microscopes Magnifying glasses Light-pointers Optical instruments Spectacles Liquid crystals Electrochromic cells Illuminating scene for taking photographs Cameras Contact photographic printing Projection photographic printing Clocks Time indicating by electric lamps Time signalling by electric lamps Visible signalling or calling systems Actuation of fire alarms Traffic lights Illuminated signs Advertising or display means on roads or walls , Aircraft advertising Advertising on ships Illuminated advertising on or in specific articles Indicating elements of instruments Indicating lamps in circuit-breaker switches Indicating lamps in fuses Lighting of aerials Coupling devices with built-in light bulbs Pulse counter or frequency divider indicators using glow-discharge lamps Illuminating of telephone substation equipment In this class, the following term is used with the meaning indicated: "steam" covers also other condensable vapours, e.g. mercury, diphenyl, diphenyl oxide. In this class, the following terms or expressions are used with the meanings indicated: "combustion" means the direct combination of oxygen gas, e.g. in air, and a burnable substance. Any other heat-producing combination of chemical substances, e.g. hydrogen peroxide and methane, iron oxide and aluminium, is covered by section C or by subclass ; "combustion chamber" means a chamber in which fuel is burned to establish a self-supporting fire or flame and which surrounds that fire or flame; "burner" means a device by which fluent fuel is passed to a combustion space where it burns to produce a self-supporting flame; "air" means a mixture of gases containing free oxygen and able to promote or support combustion. In this class, the following terms are used with the meanings indicated: "stove" includes apparatus which may have an open fire, e.g. fireplace; "range" means an apparatus for cooking having elements that perform different cooking operations or cooking and heating operations. This class covers: furnaces, kilns, ovens, retorts, open sintering apparatus and other similar apparatus for heat treatment of materials or articles, and details or accessories therefor, in general; the arrangement of electrical heating elements in or on furnaces. This class does not cover: combustion apparatus per se, i.e. apparatus for direct combination of oxygen gas and a burnable substance; electrical heating elements per se; processes carried on within the furnaces. In this class, the following term is used with the meaning indicated: "furnaces" covers kilns, ovens, or retorts. In this class, the following expressions are used with the meanings indicated: "heat exchange" means the heating or cooling of a fluid or fluent solid by direct or indirect contact with a heated or cooled fluid or fluent solid; "heat transfer" means the heating or cooling of a fluid or fluent solid by direct contact with a heated or cooled surface or body. Apparatus using heat exchange or heat transfer (as defined in Note (1) above) for specific purposes is classified either in subclass or in the appropriate subclasses of, for example, classes , , , , or ; if no such other subclass is appropriate, such apparatus is classified in subclass or . This class covers also means for practice and training which may have aspects of simulation, e.g. in apparatus for so-called "military games", although simulators are generally covered by class . In this class, the following terms or expressions are used with the meanings indicated: "smallarm" means a firearm which is generally held with one or both hands for firing, but this term also includes a light machine-gun which may be supported on a tripod or the like during firing; "gun" means any weapon having a barrel and a trigger or firing mechanism for projecting a missile; it may be a piece of ordnance or a smallarm. It may use combustible or explosive propellant charges, air pressure, electromagnetism or other propulsive forces; "revolver-type gun" means a gun having a revolving drum magazine, the chambers of which are used successively as firing chamber; "revolver" means a revolver-type pistol; "semi-automatic firearm" means a firearm from which one shot is fired after actuation of the trigger and which then returns to a condition for firing a subsequent shot upon renewed actuation of the trigger; "automatic firearm" means a firearm which will continue firing so long as the initial firing pressure is maintained on the trigger; "sighting" means bringing into visual coincidence a direction defined by a so-called "sighting" device with the direction of a target; "aiming" means bringing a weapon to a direction differing from the sighting direction by corrections in order that the projectile may hit the target; "laying" means setting a weapon in the correct position for hitting a target. Attention is drawn to the definitions of "projectile", "missile" and "rocket" given in Note (2) following the title of class . This class covers also means for practice or training which may have aspects of simulation, although simulators are generally covered by class . In this class, the following terms or expressions are used with the meanings indicated: "primer" effects the first explosive step in the sequence of explosion; "percussion cap" means a primer which is struck to explode; "igniter" effects the first spark-producing or heat-producing step but may not be explosive; "firing-means" or "initiator" (used respectively in the arts of weaponry and blasting) means a device acting directly on the primer, which device may or may not form part of the fuze; "detonator" or "detonator charge" means a charge used to amplify the explosion of the primer; "fuze" means an assembly or mechanism which incorporates safety and arming means in order that the explosion can only take place under certain conditions; this assembly or mechanism determines also the moment (instantaneous or delayed) or the manner, e.g. impact, proximity, hydrostatic pressure, of the firing; "ammunition" covers propulsive charge and projectile whether or not forming a single body, unless otherwise made clear; "projectile", "missile" or "projectile or missile" means any body which is projected or propelled; "guided missile" means projectile or missile which is guided during at least part of its trajectory; "rocket" means projectile or missile which is self-propelled, during at least part of its trajectory, by a rocket engine, i.e. by a jet-propulsion engine carrying both fuel and oxidant therefor; "fuse" or "fuse cord" means a continuous train of explosive enclosed in a usually flexible cord or cable for setting-off an explosive charge in the art of blasting.