card, as it was placed successively with each of its sides downwards.  The result is a photograph having a sharply-defined cross surrounded by four discs of precisely uniform tint, and between each pair of arms of the cross there is a very faint dot.  This photograph shows many things.  The fact of its being a composite is shown by the four faint dots.  The equality of the successive periods of exposure is shown by the equal tint of the four dots.  The accuracy of adjustment is shown by the sharpness of the cross being as great in the composite as in the original card.  We see the smallness of the effect produced by any trait, such as the dot, when it appears in the same place in only one of the components:  if this effect be so small in a series of only four components, it would certainly be imperceptible in a much larger series.  Thirdly, the uniformity of resulting tint in the composite wafer is quite irrespective of the order of exposure.  Let us call the four component wafers A, B, C, D, respectively, and the four composite wafers 1, 2, 3, 4; then we see, by the diagram, that the order of exposure has differed in each case, yet the result is identical.  Therefore the order of exposure has no effect on the result.

|----------+------------------------------------|
|Composite.|Successive places of the Components.|
| 1     2  | A    B | D    A | C    D | B    C  |
| 4     3  | D    C | C    B | B    A | A    D  |
|===============================================|

In 1 it has been A, D, C, B, " 2 " B, A, D, C, " 3 " C, B, A, D, " 4 " D, C, B, A,

I will next show a series consisting of two portraits considerably unlike to one another, and yet not so very discordant as to refuse to conform, and of two intermediate composites.  In making one of the composites I gave two-thirds of the total time of exposure to the first portrait, and one-third to the second portrait.  In making the other composite, I did the converse.  It will be seen how good is the result in both cases, and how the likeness of the longest exposed portrait always predominates.

The next is a series of four composites.  The first consists of 57 hospital patients suffering under one or other of the many forms of consumption.  I may say that, with the aid of Dr. Mahomed, I am endeavouring to utilise this process to elicit the physiognomy of disease.  The composite I now show is what I call a hotch-pot composite; its use is to form a standard whence deviations towards any particular sub-type may be conveniently gauged.  It will be observed that the face is strongly marked, and that it is quite idealised.  I claim for composite portraiture, that it affords a method of obtaining pictorial averages, which effects simultaneously for every point in a picture what a method of numerical averages would do for each point in the picture separately.  It gives, in short, the average tint of every unit of area in the picture, measured from the fiducial