I'm not entirely sure. Here is his description from C.C. Miller 50 years among the bees Page 107
Original Miller Feeder
Most of my feeders are of the original patter (Fig 40). At Fig. 41 is seen one of them dissected. The lower part is an ordinary section-super. On this rests the feeder proper, with the little board at one end removed, also the little board at one side, so as to show the inside wall under which the syrup may flow, and the outside wall, which lacks enough of coming to the to so that the bees can come over it and go down into the feed.
Improved Miller Feeder.
The Improved Miller feeder of the catalogs, instead of being all in one has two parts, and the bees go up through the middle. I thought it was an important improvement to allow the bees to go up the middle instead of up the two sides because the heat ought be be greater at the middle. After a thorough trial of the two side by side, I am obliged to admit that the improvement is one in theory only, and that the bees go up the sides whenever they will go up the middle, and it seems a little batter to have the feed all in one dish.
I don't see any floats. I think it's the typical arrangement where the bees have access to only a small area of the syrup and can't get to the middle, by the gap being too small for a bee but large enough for the syrup. Probably there are better pictures and descriptions given somewhere in the bee journals etc.
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