The Sketch
 

A single teacher can make a huge difference.  Teachers get young humans at a pliable stage, and what they do molds their pupils at a fundamental level.  Justin Tolman recognized a potential in Philo, and made materials available to him which he would not have access otherwise; both the materials and the gesture had a galvanizing effect.
1921 drawn for teacher Justin Tolman (not quite life-size here)

Sketch drawn on a notebook page which accompanied Philo's explanation of the image dissector tube (camera tube) to Justin Tolman.  This is not the original, that has disappeared, but this is the closest we can come.  This is pencil on paper, and is from a 2nd generation photocopy.  I should make a point that the blacks have been augmented to read better on this site, the copy I have has no real blacks, it is more like real pencil and made up of grays.

Interesting to note that all the elements in the working image dissector are here, and none that do not belong, and, in the patent, there are none that are not drawn here.  Definitions of "optical image" and "electron image" are key descriptions of internal changes made which are necessary to transform a regular picture made of light into picture made of a serial train of electrical charges ... in effect, the television camera has already been invented, just not yet proven (built). 

Magnetic defection, electrostatic deflection, aperture of analysis, anode, photocathode and a lens are depicted here in one manner or another, even the points where wires must penetrate the glass are shown with the extra bead of glass necessary at that point.  Remarkable.

To clear up a point I commonly run into:

At some time in the past, maybe when this image was in a printing shop being readied for the press and the image is reversed in value, someone thought that it was a chalk board drawing, and it is almost always used in conjunction with Justin Tolman's name and he teaches school and school's use chalk boards ... for whatever reason, I run into this graphic printed in reverse and represented as a chalk board drawing, and while I have to say it really does look like a chalk board drawing when reversed, IT ISN'T.  Also, while I'm correcting the record, I do suspect where the original wound up, and I am certain it is right where it belongs.