A Test to Demonstrate the Unique Mechanical Properties
Taking Place in the Radiometer
Laurence (Lance) Thompson

The purpose of my paper is to call attention to the unique mechanical properties of the radiometer. The radiometer is a glass bulb with a partial vacuum of rarefied gases with enclosed vanes of reflective and non reflective surfaces which rotate in response to light or radiant energy heating the non reflective vane surfaces.

In 1879 J. Clerk and O. Reynolds found a lateral motion of the heated, energized gas molecules on the non reflective side of the vane surface results in the energized gas molecules slipping over the vane edges and exerting a force on the vane edges. The energized heated molecules from the non reflective side "...strike the edges obliquely and impart a higher force than the colder molecules". Thus exerting a net force on the radiometer vane edges. The rarefied gas molecules then slip back toward the opposite direction on the other side of the vane. (1)

In contrast to conventional engines with attached parts, the rarefied gas molecules of the radiometer would be semi independent of the vane surfaces. Once a force is imparted to the vanes there would be no need for another offsetting force as the original imparting of momentum into the vanes would be the offsetting force. Thus the vanes can continue to spin.

I feel another factor allowing the radiometer vanes to continue to spin is the oblique imparting of force on the radiometer vanes is not "head on". As the force would be applied at an oblique angle, this could be somewhat similar to the tacking of a sail boat. The sail does not meet the wind head on, but at an angle to gain energy to reach a point upwind of the original position. I feel both the semi independence of the rarefied gas molecules from the radiometer vanes and the oblique angle of the application of force work to ensure that the radiometer vanes can continue to spin (and at rates of up to 2000 to 3000 rpm).

Before continuing, I wish to address a possible objection as one might say the spinning of the vanes could drive the re- circulation patterns. Yet, in support of slip effects driving both the rotation of the radiometer vanes and the re- circulation of cooled molecules would be William Crookes' original observations (before inventing the radiometer). Crookes found on weighing objects in a partial vacuum that the rarefied gas reactions initially took place on objects which were not free to rotate. (2)

I feel the key to the following testing of the mechanical properties taking place in the radiometer is that the equal and opposite reactions of physics would be satisfied by this direct imparting of momentum into the vane edges as the offsetting force to the slip effects exerted by the energized gas molecules. No other off setting force would be present to impede the spinning vanes (except a little back pressure from the rarefied gas atmosphere itself).

In effect, I feel the implication of the spinning vanes of the radiometer could be a simple "engine" in which the molecular momentum of the rarefied gas molecules would be converted directly into the momentum of the radiometer vanes.

The premise for the following proposed testing is if a force can be exerted on the radiometer vane edges via slip effects then a similar force could be exerted on attached "surfaces" in a closed cylinder of rarefied gases to likewise cause the propulsion of a body.

(Please refer also to the following diagram.)

In the radiometer and in the testing I note once the rarefied gas molecules impart momentum into the vanes via the vane edges that the gas molecules, in losing energy, would become cooled in this process and could represent the "exhaust" side of such a simple engine.

In the wider spacing of the rarefied gas molecules, as compared to a full atmosphere, I feel it is likely that heated and cooled molecules could exist in closer proximity to one another for the re-circulation of cooled molecules back on to the heated, non reflective surface. In the radiometer and in the testing ample spacing appears available for the re- circulation of the rarefied gases.

Initial Testing

The initial testing is to take place at room temperature in a partial vacuum with similar rarefied gases as the radiometer. The testing is to be preformed by experienced persons with a knowledge of vacuum safety considerations. In determining the most effective surface, say a 12 X 12 cm "surface" of similar composition as the radiometer vanes can be used. This surface is to be tested with varying proportions of openings to allow slip effects to take place. The most effective shape and size of the openings for slip effects can then be determined.

In the initial testing the surface can be mounted vertically with gussets in each corner for wire guides. I would anticipate in a similar rarefied gas environment, similar slip effects around the edges of the openings in the surface. Hence in response to a light beam applied perpendicularly on to the non reflective side, the surface should likewise be propelled along the wire guides and away from the light source. I feel such an initial verification would demonstrate the non rotational nature of the slip effects and would also demonstrate, as in the spinning radiometer vanes, that no additional offsetting force would be present to stop the forward propulsion of the surface.

The force/power generated on the surface under varying light intensities could also be calculated to determine if sufficient power could be generated to run the following closed cylinder test in the open air, under a full atmospheric pressure.

Other notes for the testing

1. The openings in the surfaces for slip effects should be of sufficient size to allow for circulation of de-energized, cooled gas molecules back through the openings. (Note: it is likely without the crowding effects of a full atmosphere that cooled and energized molecules could be in closer proximity for such re-circulation patterns.)

2. The maximum distance between openings in the surfaces could be compared as to when slip effects become impeded. Also how close could a holed surface be in proximity to a fixed, solid surface before slip effects would become impeded.

3. Although not necessary in the testing, a thicker insulation material could be used and a non reflective material applied to both sides of the surfaces. I feel if light or radiant energy would be applied directionally to one side and kept away from the opposite side that slip effects could still be maintained. Thus it could be possible to reverse direction of movement by reversing the direction of the energy source.

4. Although self evident in the radiometer and in the test, the vanes and the surfaces are to be free to move in response to the application of force/power. Too much mass or inertia would result in heating of the surfaces without power being inputed into the momentum of the vanes or into the surfaces. (The energy would instead be transferred to molecular motion.)

In the test the surfaces, which are attached within a light weight, closed cylinder, would still be free to move, though not individually, but as a unit with the closed cylinder.

In continuing to the test I note the radiometer vanes do not rotate if a full atmosphere were present due to the crowding effects of the gas molecules. Yet this would not preclude the possibility, with sufficient force generated internally by a partial vacuum of rarefied gases acting on attached surfaces in a closed cylinder, that such a closed cylinder might be able to develop sufficient power to be propelled in the open air under a full, external atmosphere.

My radiometer after allowing for up to 50% space surrounding the vanes for slip effects and re-circulation patterns gave an incipient, low end figure of approximately 0.1 gram/sq cm which could be accelerated on applying a weak light beam on to a vane surface. (This figure was derived upon breaking the radiometer to weigh the vanes and mounting harness.) Thus I feel at a strong light intensity it could be possible to generate substantially more power.

In the following test the force generated could be increased as solar energy would constantly strike the surfaces. Also less back pressure from the rarefied atmosphere itself could result on the attached surfaces as compared to the rotating radiometer vanes.

Hence my hunch is sufficient force/power might be generated to propel such a closed cylinder in the open under a full atmosphere. (And if so, this would facilitate the design of a simple test vehicle which could be made readily available in the physics classroom to further demonstrate the mechanical properties taking place in the radiometer.

The following, basic test, is to be in a vacuum chamber in which the rarefied gas pressure would be equalized between the rarefied gases within a closed cylinder and with the external rarefied gas pressure in the vacuum chamber. This would allow the use of a very light weight, thin skinned, closed cylinder in the following test.

(Note: if sufficient force/power could be generated this test could also be demonstrated in the open air with a thick walled, substantially heavier closed cylinder.)

The test is to take place at room temperature using a strong, light weight, transparent closed cylinder of say 11+/- cm in diameter and 27+/- cm in length. (Actual size to be determined by safety and weight factors.) The rarefied gases are to be similar to the radiometer. A series of 5 circular, holed surfaces with a diameter of 10 cm each and of similar materials as the radiometer vanes can be mounted perpendicular in the cylinder on a spacing of say 5+/- cm to give a total force generating area of about 400 sq cm. This would include both solid areas and up to 50% openings as necessary in the holed surfaces for slip effects. (I have not counted the additional 0.5 cm space around each surface edge and the cylinder wall for additional slip effects).

The 5 cm spacing between the surfaces should be sufficient to allow light or radiant energy to strike the non reflective side of the surfaces.

(Note: as slip effects would be a function of heating the non reflective surfaces, it would not be necessary for the light to strike the surfaces head on. Rather a strong light beam from a high, oblique angle could be used.)

The closed cylinder can be mounted on low friction wheels or on skids on a low friction surface.

Although the force/power generated may be small, upon applying light or radiant energy on to the non reflective side of the surfaces, I feel the mechanical properties which could likely be demonstrated in this test in a vacuum chamber could be:

1. In contrast to the spinning vanes of the radiometer, it would be the closed cylinder to which the force would be directed. As the force would be applied directly on to the edges of the attached surfaces, there would be no moving parts except the rarefied gas molecules and the cylinder or "engine" itself. In this mechanical simplification, the closed cylinder would become both the "piston" and the "drive train".

(Note: this property derives from what could be the key aspect of the mechanics taking place in the radiometer - the direct imparting of momentum into the attached surfaces as the offsetting force to the slip effects of the energized gas molecules - without a need for an additional off setting force.)

2. The inertia of the closed cylinder would be the base for propulsive force. The force/power generated on the edges of the cylinder "surfaces" would be directed against the cylinder's inertia via the attached surfaces as the base for the acceleration of the closed cylinder. The closed cylinder will thus be propelled without the need of external surfaces for traction.

3. As in the force exerted on the radiometer vanes, only the input of energy would be necessary to recharge and reuse the rarefied gases in exerting a force on the "surfaces" of the closed cylinder. In this property of reusing and recharging the "propellent", the propulsion of the closed cylinder would discharge no external exhaust gas. (End)


1. "How Does A Light-Mill Work?, Updated 6/12/97 by PEG, original by Philip Gibbs 7/2/96. (on the internet.)

2. Dictionary of Scientific Biography. V.III,1974, pgs 476-7.

A Speculation

Although the force exerted in the radiometer may be small, I feel if these mechanical properties could be made available as within that which could be possible, perhaps other medium besides rarefied gases could be found to apply such properties to create a new class of engines.


In a paper I am writing, titled "An Accelerative Universe", the confirmation of these properties would give me grounds to postulate that an unknown form of acceleration could be taking place in galaxies to cause the accelerative expansion of the universe.

Free Use

The originality of my ideas in my paper, "A Test to Demonstrate the Unique Mechanical Properties Taking Place in the Radiometer", including my ideas previously shared with others, is given to the public domain to be freely used. (I would though appreciate a credit for my work.)

Copyright 2001/2002. Permission is given to make limited copies for distribution to those who would be interested.