Thomson kept an "opaque" object in the cathode ray tube and he saw the shadow of the object.then he decide that the cathode rays follow a rectilinear path. But Thomson also discovered that cathode rays actually consist of particles.

Suppose I keep a transparent object (such as a thick slab of glass) instead of the "opaque" object. If the cathode rays are particles, then we would still find a shadow formed behind the glass slab (the particles wouldn't be able to pass through the slab).

Numerous articles and books I've referred to insist that the experiment requires that an "opaque" object be placed inside the cathode ray tube.

However, in my example with the glass slab, "opacity" doesn't seem to be a pre-requisite for the successful implementation of the experiment. Am I right in thinking this?

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    $\begingroup$ Opaque to electrons, not to light. It is applied to both cases, although the second is the common usage since humans don't directly see electrons... $\endgroup$
    – Jon Custer
    Commented Jun 25, 2017 at 16:28


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