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 that the relativity theory shall be considered as disproved by his experiments.

A situation of unique difficulty was created by this result.

Some physicists now further developed the relativity principle, with the expectation that more precise measurements nevertheless would eventually bring a decision, while others (including me) interpreted 's result as decisive. Since all other observations alluded to the existence of some kind of relativity principle which was still unknown, I thus developed a new relativity principle, which, however, only had the character of a calculation rule. 's measurements were compatible with this principle, and (as I was thinking at that time) it was only about the investigation of the deviation of electrons flying obliquely towards the magnetic field. Here, differences with respect to 's theory should occur.

A clarification of the state of facts could only be achieved by new experiments, conducted with essentially increased precision. For that purpose, I created a new experimental arrangement, which I already described in the Physikalische Zeitschrift. The method chosen, allowed for testing my relativity principle, i.e. an investigation of the deflection of electrons flying obliquely towards the field direction, as well as testing the relativity principle and the initial theory of, thus the same question which formed the subject of 's investigation. Becquerel rays shall fly through a condenser field, and the electric force acting upon the electrons shall be compensated by superposition of a uniform magnetic field, which is parallel to the plates of the condenser. After leaving the condenser, the magnetic field alone acts upon the rays. The deflected electrons fall upon a photomicrograph film, so that the deflection can be measured. Since the force stemming from the magnetic field is proportional to the velocity of the electrons, then the compensation can only exist for a quite definite velocity, and only electrons of this velocity can traverse the condenser field undeflected, and therefore they can leave.

The details of the experimental arrangement are as follows: The condenser consists of two circular plates lying horizontally, whose diameter is ca. 8 cm and whose mutual distance amounts to ca. ¼ mm. As radiation source, a granule of radium salt in the form of a sphere (namely fluoride instead of the previously used bromide) is brought between the plates in the center of the condenser. Since the specific concentration of radium in fluoride is more than double as in bromide, the time of exposition becomes quite essentially diminished by using fluoride, which is of great importance in these experiments. The condenser is located in a cylindric tin consisting of brass, namely at half the height from the ground, so that its surfaces are located exactly perpendicular to the cylinder axis, which passes through the center of the condenser. The cylindric tin (which is very exactly formed) has an inner diameter of ca. 16 cm and an inner height of 8 cm. This tin can be airtightly sealed by sanded glass covers, so that it can be evacuated. The air pump employed was a Gaede pump, which worked excellently. By suitable drilling, the cables (being isolated from an accumulator battery) were inserted into the brass tube. The photographic plate is pressed by two springs against the interior wall of the tin. The latter can be inserted into the interior of the solenoid, whose rectangular cross-section is adapted to the dimensions of the tin. The solenoid is 103 cm long and has two windings of 103 turns each. The field strength achievable with the solenoid, was ca. 140 Gauss.

The purpose of my arrangement can be easily recognized. Since the directions of the rays are namely forming all possible angles $$\alpha$$ with the direction of the magnetic force, then the force (occurring according to 's theory) can assume all possible values. If the electrodynamic force and the electric one $$\epsilon F$$ is compensated, it is

$\frac{u}{v}=\beta=\frac{F}{v\ H\ \sin\alpha}.$