[alright1234 (OP)]

 Cavendish's experimental apparatus uses two lead spheres m1  = 158 kg and m2  = .73 kg separated by the distance of .21 m that detects a force of 1.74 x 10−7 N (≃ 2μg ) which is too small to measure in 1797 which nullifies Cavendish's experiment.

[Kryptid]

What is your evidence? Please provide a reputable source to back it up.

[evan_au]

The experiment certainly needed to be well-shielded from outside interference, and the very tiny oscillations (5mm) had to be viewed from a distance with a telescope.

Difficult, yes; but which part of the experiment do you suggest is impossible?
And then why did more sensitive recent techniques confirm his results (after an arithmetic error was corrected...).
See: https://en.wikipedia.org/wiki/Cavendish_experiment#The_experiment

[alancalverd]

Worth reading Cavendish's experimental method carefully. The torsion balance is a neat trick for applying or measuring very small forces, and in the event he only needed to measure a distance of about 4 mm, slightly complicated by the fact that the torsion rod was oscillating with a period of about 20 minutes, but no big deal in the 18th century when good telescopes and vernier scales were an everyday part of navigation equipment and there was no heavy traffic in the vicinity.

Cavendish was an experimental genius (as becomes all Peterhouse men) who also discovered hydrogen and used a null experiment to demonstrate the inverse square law of electrostatics.

[Bored chemist]

Cavendish's experimental apparatus uses two lead spheres m1  = 158 kg and m2  = .73 kg separated by the distance of .21 m that detects a force of 1.74 x 10−7 N (≃ 2μg ) which is too small to measure in 1797 which nullifies Cavendish's experiment.

The problem seems to be that Cavendish was much cleverer than you.

[alright1234 (OP)]

What is your evidence? Please provide a reputable source to back it up.

The most accurate weight measurement devise in 1797 was a balance beam that has an measurement uncertainty of approximately 1 mg.

[Bored chemist]

What is your evidence? Please provide a reputable source to back it up.

The most accurate weight measurement devise in 1797 was a balance beam that has an measurement uncertainty of approximately 1 mg.

Did you write that yourself?

It certainly isn't a reputable source.
You don't say where it's from.

In any event, clever people worked out that the 2µg isn't a weight.
So what you wrote is irrelevant.

[alancalverd]

What is your evidence? Please provide a reputable source to back it up.

The most accurate weight measurement devise in 1797 was a balance beam that has an measurement uncertainty of approximately 1 mg.

Quite possibly, but Cavendish wasn't worried about milligram uncertainty of his test masses. Weighing dense metals to +/- 1% in the kilogram range certainly wasn't a problem. 

[alright1234 (OP)]

In any event, clever people worked out that the 2µg isn't a weight.

If 2µg is not a weight (force) than what is it?

[Bored chemist]

If 2µg is not a weight (force) than what is it?

Not all forces are weights.

[alright1234 (OP)]

To test Cavendish's experiment, Cavendish's .73 kg lead sphere is suspended using a thin titanium wire and place .01 mm from Cavendish's larger lead sphere (158 kg). A laser is used to detect the change in the angle of the wire that is suspending the .73 kg lead sphere (fig 32a,b). As the 158 kg lead sphere is slowly rolled away from the smaller .73 kg suspended lead sphere no measurable change in the angle of the wire is observed which nullifies Cavendish's experiment.

[Bored chemist]

To test Cavendish's experiment, Cavendish's .73 kg lead sphere is suspended using a thin titanium wire and place .01 mm from Cavendish's larger lead sphere (158 kg). A laser is used to detect the change in the angle of the wire that is suspending the .73 kg lead sphere (fig 32a,b). As the 158 kg lead sphere is slowly rolled away from the smaller .73 kg suspended lead sphere no measurable change in the angle of the wire is observed which nullifies Cavendish's experiment.

Why did you post that meaningless dross?

[alright1234 (OP)]

The experiment certainly needed to be well-shielded from outside interference, and the very tiny oscillations (5mm) had to be viewed from a distance with a telescope.

Difficult, yes; but which part of the experiment do you suggest is impossible?
And then why did more sensitive recent techniques confirm his results (after an arithmetic error was corrected...).
See: https://en.wikipedia.org/wiki/Cavendish_experiment#The_experiment

Cavendish did his experiment outdoors in a old brick outhouse without heating. The question is not if Cavendish experiment is valid now but in 1797 was it valid.

[Bored chemist]

Cavendish did his experiment outdoors in a old brick outhouse

Which?
Outdoors, or in a building?

Do you realise that " without heating" removes thermal currents?
That's the best way to do it.
Did you not think that through?

Seriously, why are you even discussing this?
You clearly have no clue what you are on about.

[Bored chemist]

in 1797 was it valid.

Yes.

[alright1234 (OP)]

In 1797, they could measure the force equivalent to a dust particle? Why do dust particle not stick to the side of a granite cliff.

[Bored chemist]

In 1797, they could measure the force equivalent to a dust particle?

Yes. We know this because... Cavendish did it.
And just because you choose not to accept it, doesn't stop it being true.

Why do dust particle not stick to the side of a granite cliff.

I would assume that they do.
They certainly stick to the mirror in my bedroom.
I doubt the dust can tell the difference between one smooth silicate surface and another.

[alancalverd]

The force difference in the original Cavendish experiment was about 25 μg, not 2.

Cavendish actually set out to measure the mean density of the earth, following Maskeleyne's earlier measurement of the mean density of Schiehallion. So the precise measurement of small gravitational forces was a current matter of interest, not impossibility.

Given that the value of G calculated from Cavendish's results  is within 1% of the current consensus value, he was either incredibly lucky or an exceptional experimental scientist. In view of his discovery of hydrogen and the noble gases, and his proof of the inverse square law of electrostatics to better than 0.1%, I think the latter is the more probable.

What kind of idiot attempts to measure the angle of twist of a tungsten filament with a laser? The kind that thinks moving the large sphere will cause the small one to rotate. Gravity isn't like viscosity.

[Bored chemist]

What kind of idiot attempts to measure the angle of twist of a tungsten filament with a laser?

The sort who thinks protons are not real

[alright1234 (OP)]

Could a force (2 ug or so) equal to the weight of a single dust particle really twist and turn Cavendish's iron rod?