is worth as much; and yet, as has been shown, the portions when separated had relatively only a small value; Soult's portion, for instance, which was bought in for £200, selling subsequently for only £500.

Few, if any, other pictures possess so strange and interesting a history-a history with so singular a termination! How much, too, is its present owner to be congratulated for the lustre and importance added to the Lockinge collection, in consequence of the remarkable circumstances that enabled Lord Overstone to become its possessor!

I cannot close this story without acknowledging the assistance that has been so willingly given me by several friends and acquaintances, and by others, who, though strangers to me, were kind enough to take an interest in my researches.

CHAPTER XXIII.

The Autotype Process: An interesting and valuable Process explained.

I HAVE as yet avoided speaking of any particular photographic process, but here propose to make an exception in favour of the Autotype, the discovery and introduction of which has been such a distinct gain and important aid to photography.

As a process it is very simple, and yet so astonishing when shown the first time, that it is thought a short description of it will be acceptable.

As soon as the instability of all the ordinary photographic methods was recognised, it became the end and aim of a large number of earnest workers, in all parts of the world where photography was known, to provide a remedy; and, by the cumulative effect of successive inventions and improvements, means were found by which this end was attained.

Gelatine plays an important part in many photographic inventions, and does so in the autotype process, which is entitled to take the highest rank on account of the beauty and completeness of its results.

The word "autotype" signifies self-printing, a term adopted by those who proposed and intended to express the power of producing, independently of any aid or action other than that which belongs to the process, a picture in "monochrome," whether, to use the language of a wellknown writer-the late Mr. Tom Taylor-" it be in red or black chalk, indian ink, sepia, common ink-in short, any colouring matter that can be incorporated with gelatine;" and he adds "as only the pigments which are the most permanent that are known to art are used in the process, the finished autotype is as permanent as the pigment which is selected for its production."

As will be seen from this extract, the colour of an autotype picture is due alone to the pigment that is used. When colour has been incorporated with gelatine the preparation is then called "pigmented gelatine," and with it paper suitable

for the purpose is coated. If not needed for immediate use it is allowed to dry, and in that state will keep any reasonable time, light having no action upon it; it may even, without injury, be soaked in cold water and again dried, but if put into hot water the gelatine is dissolved and the pigment washed away.

Here comes in the particularly striking part the process, which is as simple as it is interesting, but which, as will be seen, is in its results most important. To render a sheet of pigmented gelatine photographic-which means to render it sensitive to the action of light-it has to be immersed for a short time in a solution of bichromate of potass. This must be done in a room where there is no actinic light, and where it can be dried and kept until needed for use. In that state, as far as is apparent, there is no change or alteration in the original preparation.

"bichromatised

But expose the film of gelatine" to light, and at once a most important change is set up; that is, the film which before exposure to light was readily soluble, becomes by exposure to it, insoluble. So that a sheet of

bichromatised gelatine, having been subjected to light in an exact and equal degree on every portion of it, an equal degree of insolubility supervenes. But the effect that is produced by placing between it and the light's action varying degrees of resistance is far more important and wonderful.

Such action may be epitomised thus:—The degree of insolubility that is attained and the degree of solubility that is preserved is in exact proportion to the degree in which light is shut out from or let into the coating of the bichromatised gelatine; that is, suppose that, intervening between it and the light, there is a means of resistance constructed on an exact scale of gradation of tones, running from transparency to opacity, that resistance would be translated into the same exact gradations of the pigment which had been mixed with the gelatine.

This can possibly be made clear by describing one of the experiments I made at the Royal Institution. A sheet of plate glass, 12 by 10 inches in size, was in the first place taken; then seventy-eight slips of tissue paper were used, each 1 inch wide and 10 inches long; on the first inch of the glass I fixed, one above the other,