13 (amdg_13.gif)] Just in front, and between the sitter and {200} the reflector, upon a proper stand, were used those paper muslin screen before described; also screens of tissue paper.

These screens, however, when they were used, required so much time for a sitting, that some other medium, as a protection to the eyes, became absolutely necessary.

The most plausible thing that suggested itself was blue glass; but, as this could not be found, numerous were the expedients proposed by the friends of the art, who from time to time visited our rooms.

At the suggestion of Professor Mapes (who is ever ready to assist those in perplexity), a trough of plate glass s, about twenty-eight inches square in the clear, and from three to four inches thick, was filled with a solution of ammonia sulphate of copper, and mounted on the frame as in the sketch, which, for a time, answered extremely well; soon, however, decomposition of this solution became apparent from the increased length of time required for a sitting, although to the eye of an observer, no visible cause for such long sittings could be pointed out.

Professor Mapes being appealed to, suggested that to the above solution a little acid be added which acted like a charm--shortening the time for a sitting from six, eight, or ten minutes to that of about one.