860. This device is a watchmaker's Geneva glass gauge.
According to the Source Book for Rule Collectors:
The sizes of watch glasses are expressed in either Geneva or Lunette measurement, two different standards developed in Switzerland. Geneva measurement is expressed in units and 16ths, where a unit is approximately equal to .0825 of an inch, thus a watchmaker would say that a Waterbury watch takes a 18 1/16 Geneva crystal.
The crystal being measured would be placed on the surface of the gauge, its lower edge resting against the step, and its diameter determined by what graduation line it touched at its upper edge.
Thanks to Virginia White, Mid-West Tool Club "What's It" Columnist, and Otto van Poelje for providing the answer to this one.
Another Geneva glass gauge can be seen here on ebay, where it is theorized that the pin on the side measures the inside height of the dome of the glass.
861. Double-harpoon hay fork, used for the same purpose as a single harpoon, to get hay up to the loft. There are hundreds of patents for hay harpoons, the closest that I found to the one in the photo is number 318,416.
The double harpoon worked better with short-stemmed hay crops, where the single harpoon (below) was not useful.
862. Chopping machine, the photo on the link has a good view of the other side, showing the vertical shaft, gears, and belt.
863. Wind damper, stops the phone lines from swinging too much.
I shot this photo several months ago, didn't know what it was, turns out that it's also a wind damper, patent number 4,663,496. It's difficult to tell from the picture, but it hangs under the line with each side angled down about 45 degrees.
864. Still unidentified, looks like some type of laboratory timer.
865. Mastercool infrared thermometer, similar to the one in this article at Cool Tools.
749. This plate is a cover for a post office box, a reader of this site has used one just like it, here is their description:
The 2 holes along the bottom were for 2 small knobs which worked as a combination lock device. The knob on the left had the letters A-M along the outer part of the circle. The right, N-Z. The knob above was where you'd turn to pull open/close the post office box door. The large hole was where you could look through a thick piece of glass the metal was mounted on as to see if they'd put the day's mail out yet. It is my understanding that this sort of cover to post office boxes was used from the 1890's thru the 1920's. It is almost identical to the one we used day after day in the old post office here in Weaverville, NC. The only difference was that the top opening where you'd look in to see if the mail had been put out yet was square and the one in your picture is round.
Last week's set is seen below, click here to view the entire post:
More discussion and comments on these photos can be found at the newsgroup rec.puzzles.