[Illustration]

The rollers are supported on springs, _a¹ a¹_, to render their motion
equal; they are turned by the milled heads, _m m_, and clamped when each
fresh sheet is brought into position by the nuts, _a² a²_. _c_, is a board
which is pressed forward by springs, _c¹ c¹_, so as to hold the sheet to be
exposed, and keep it smooth against the plate of glass, _d_; when the sheet
has been exposed, the board is drawn back from the glass in order to
release the exposed sheet, and allow it to be rolled on the exposed roller;
the board is kept back while this is being done by turning the square rod,
_c²_, half round, so that the angles of the square will not pass back
through the square opening until again turned opposite to it; _e e_ are
doors, by opening which the operator can see (through the yellow glass, _y
y_) to adjust the position of the sensitive sheets when changing them.

The remarkable similarity of such a slide to the automatic printing-frame
described last week will strike the reader; and, like the printing-frame,
it possesses the advantage of speed in working--no small consideration to
the photographer in a distant, and possibly hostile, country.

Fine paper well sized with an insoluble size and coated with a sensitive
emulsion is, we believe, the very best material to use in the roller slide;
and such a paper might be made in long lengths at a very low price, a
coating machine similar to that constructed for use in making carbon tissue
being employed. We have used such paper with success, and hope that some
manufacturer will introduce it into commerce before long. But the question
suggests itself, how are the paper negatives to be rendered transparent,
and how is the grain of the paper to be obliterated? Simply by pressure, as
extremely heavy rolling will render such paper almost as transparent as