Figure 14.—Surfacing machine used by Peate. (From Preston, fig. 4.)
On June 1, 1895, Standard Plate rendered Peate an invoice, not for $1600, but for $450. Evidently their work was done at cost. The disc was now removed to Greenville where Dr. Peate had erected a shop to grind, polish, and figure it. As the disc was slightly out of round the first operation was to make it perfectly circular. Peate did this roughly by spalling off pieces of the edge with his bricklayer’s hammer. The final rounding was done with the aid of the iron hoops that had made the mold. Dr. Peate fed steel shot between the edge of the disc and the iron semicircles. He rotated the disc on the turntable and thus rounded it off.
After this had been done he commenced the rough grinding. Using the large checkerboard tool, steel shot, and levigated emery Dr. Peate ground out a rough hollow. This took only a few days. George Howard stated that the depth of the concavity was about ⅝ inch and the shape correct to within about 1/10,000 inch. The calculated concavity of the mirror would be 6/10 inch. Peate evidently used the usual method in polishing the large mirror, that is, he covered the tool face with pitch and used rouge (iron oxide) as the abrasive. This method had been used for many years before this time and is still in use today.
The figuring, which consists of removing high spots to achieve a truly parabolic contour, probably took the longest time to complete. A mirror must be continually tested as this polishing is being done, and since the polishing warms the glass and distorts its shape, it is necessary to allow a long time for the glass to cool before it can be tested. Peate estimated that polishing and figuring the mirror took 750 hours.[36]
We do not have a really accurate account of how he tested the mirror. Unfortunately none of the eyewitnesses to these tests had any knowledge of optics or of standard testing procedure. The information of those who had such knowledge is all at least secondhand and sometimes even more remote. J. W. Fecker, successor to Brashear,[37] who was one of a group that examined the mirror in 1923, states that Peate did not use the knife edge test but that he did use a pin with a hole in its head in one of the tests used at that time.
A variety of different tests and diversions with the mirror have been reported. Dr. Peate would entertain visitors in various ways. One of these was to train the mirror on an apple orchard in a valley a few miles away. In another Peate would pull out one of his whiskers and hang it on a fence nearly a quarter of a mile away. Peate himself tells of the time spent in testing the mirror, but does not go into detail about the procedure. He does mention a testing table that stood about 75 feet away from the revolving table on which the mirror rested. He says further that the mirror was tested “in all ways known, in the shop and on a pin and a watch dial a thousand feet distant.” Of these only the pin test seems to have been a conventional one.[38]
After the polishing, the mirror was silvered. Said Peate: “It was silvered and tried on the heavens in the starless region under Corvus, and under the very imperfect management of the mirror on telescopic stars, the report was as good as could be expected.”[39] Dr. Peate must have spent some time testing it on the stars. The mirror was evidently completed sometime late in summer of 1897, and when Peate was satisfied that it was as perfect as possible, he made arrangements to send it to American University. He also designed the shipping case to protect it on the trip to Washington. It is described in the University paper as follows:[40]
This consists of a box in which the glass is packed and a wheeled truck in which it is swung. It is swung on its edge by iron bands, which go around it over an iron belt which encircles it.
After waiting for the case, he encountered a further delay by reason of the fact that the express company had no office at Greenville. However the great glass finally was loaded on the train, and on August 24, 1898, it arrived safely at American University.