no, i've seen the sketch (tho not the expensive version)
it seems these things were "maxwell's disks" (james clerk maxwell?) "colored 'red,' 'yellow,' 'white' and 'black'" -
then apparently you varied the speeds of the different disks (?) until you got some close approximation to what you want to match...?
i guess then you had to look at some kind of table to convert the speed of rotation back to colour/shade...?
i'll see what else i can come up with & let you know -

"Anita Cohen-Williams" <[log in to unmask]> schrieb:
> And, one for sale!