[Lonesome in Massachussets]

Antiparticles were first discovered in cloud chambers. The antielectron was deflected the wrong/opposite way in a magnetic field. One could infer the mass/charge ratio from the radius of curvature. It had the same mass/charge ratio as the electron, but the wrong charge. Discovery photograph from wikipedia:

Cloud chamber photograph of the first positron ever observed. The thick horizontal line is a lead plate. The positron entered the cloud chamber in the lower left, was slowed down by the lead plane, and curved to the upper left. The curvature of the path is caused by an applied magnetic field that acts perpendicular to the image plane. The higher energy of the entering positron resulted in lower curvature of its path. Original caption: A 63 million volt positron (Hρ = 2.1×105 gauss-cm) passing through a 6 mm lead plate and emerging as a 23 million volt positron (Hρ = 7.5×104 gauss-cm). The length of this latter path is at least ten times greater than the possible length of a proton path of this curvature.

[Tell It Right]

Thank you so much for telling me this.

By "cloud chamber photograph", is that a literal photograph (the capturing of light). Or is that a derived "image" like from an MRI (where the "I" in "MRI" stands for "image" but it's not a literally image made from light, it's a topography derived from detecting deviations in the magnetic field).

If it's a literal photograph that gives me a whole new perspective and respect for the accuracy of results from experiments like this.