As regards the fiducial lines, they might be drawn on the glass screen; but black lines are not, I find, the best.  It is far easier to work with illuminated lines; and it is important to be able to control their brightness.  I produce these lines by means of a vertical transparency, set in an adjustable frame, connected with A, and having a gas-light behind it.  Below the eye-hole e, through which I view the glass-screen g, is a thin piece of glass set at an angle of 45 deg., which reflects the fiducial lines and gives them the appearance of lying on the screen, the frame being so adjusted that the distance from the thin piece of glass to the transparency and to the glass-screen g is the same.  I thus obtain beautiful fiducial lines, which I can vary from extreme faintness to extreme brilliancy, by turning the gas lower or higher, according to the brightness of the image of the portrait, which itself depends on the density of the transparency that I am engaged upon.  This arrangement seems as good as can be.  It affords a gauge of the density of the negative, and enables me to regulate the burners behind it, until the image of the portrait on g is adjusted to a standard degree of brightness.

For convenience in enlarging or reducing, I take care that the intersection of the vertical fiducial line with that which passes through the pupils of the eyes shall correspond to the optical axis of the camera.  Then, as I enlarge or reduce, that point in the image remains fixed.  The uppermost horizontal fiducial line continues to intersect the pupils, and the vertical one continues to divide the face symmetrically.  The mouth has alone to be watched.  When the mouth is adjusted to the lower fiducial line, the scale is exact.  It is a great help having to attend to no more than one varying element.  The only inconvenience is that the image does not lie in the best position on the plate when the point between the eyes occupies its centre.  This is easily remedied by using a larger back with a suitable inner frame.  I have a more elaborate contrivance in my apparatus to produce the same result, which I need not stop to explain.

For success and speed in making composites, the apparatus should be solidly made, chiefly of metal, and all the adjustments ought to work smoothly and accurately.  Good composites cannot be made without very careful adjustment in scale and position.  An off-hand way of working produces nothing but failures.

I will first exhibit a very simple but instructive composite effect.  I drew on a square card a circle of about 2-1/2 inches in diameter, and two cross lines through its centre, cutting one another at right angles.  Round each of the four points, 90 deg. apart, where the cross cuts the circle, I drew small circles of the size of wafers and gummed upon each a disc of different tint.  Finally I made a single black dot half-way between two of the arms of the cross.  I then made a composite of the four positions of the