A chronograph is held in the other hand, whose index begins to travel the moment the finger presses a spring, and stops instantly on lifting the finger.  The two instruments are worked simultaneously; the chronograph checking the time allowed for each exposure and summing all the times.  It appears from several trials that the effect of 1000 brief exposures is practically identical with that of a single exposure of 1000 times the duration of any one of them.  Therefore each of a thousand components leaves its due photographic trace on the composite, though it is far too faint to be visible unless reinforced by many similar traces.

The composites now to be exhibited are made from coins or medals, and in most instances the aim has been to obtain the best likeness attainable of historical personages, by combining various portraits of them taken at different periods of their lives, and so to elicit the traits that are common to each series.  A few of the individual portraits are placed in the same slide with each composite to give a better idea of the character of these blended representatives.  Those that are shown are (1) Alexander the Great, from six components; (2) Antiochus, King of Syria, from six; (3) Demetrius Poliorcetes, from six; (4) Cleopatra, from five.  Here the composite is as usual better looking than any of the components, none of which, however, give any indication of her reputed beauty; in fact, her features are not only plain, but to an ordinary English taste are simply hideous. (5) Nero, from eleven; (6) A combination of five different Greek female faces; and (7) A singularly beautiful combination of the faces of six different Roman ladies, forming a charming ideal profile.

My cordial acknowledgment is due to Mr. R. Stuart Poole, the learned curator of the coins and gems in the British Museum, for his kind selection of the most suitable medals, and for procuring casts of them for me for the present purpose.  These casts were, with one exception, all photographed to a uniform size of four-tenths of an inch between the pupils of the eyes and the division between the lips, which experience shows to be the most convenient size on the whole to work with, regard being paid to many considerations not worth while to specify in detail.  When it was necessary the photograph was reversed.  These photographs were made by Mr. H. Reynolds; I then adjusted and prepared them for taking the photographic composite.

The next series to be exhibited consists of composites taken from the portraits of criminals convicted of murder, manslaughter, or crimes accompanied by violence.  There is much interest in the fact that two types of features are found much more frequently among these than among the population at large.  In one, the features are broad and massive, like those of Henry VIII., but with a much smaller brain.  The other, of which five composites are exhibited, each deduced from a number of different individuals, varying four