Next in importance to glass as a support comes paper, and it is quite easy to understand that the tourist in out of the way parts might be able to take an apparatus containing a roll of sensitive paper, when it would be altogether impracticable for him to take an equivalent surface of coated glass, and in such a case the roller slide becomes of especial value.

The roller slide of Melhuish is tolerably well known, and is, we believe, now obtainable as an article of commerce.  The slide is fitted up with two rollers, a a, and the sensitive sheets, b b, are gummed together, making one long band, the ends of which are gummed to pieces of paper always kept on the rollers.  The sensitive sheets are wound off the left or reserve roller on to the right or exposed roller, until all are exposed.

[Illustration]

The rollers are supported on springs, a a, 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, a squared a squared. c, is a board which is pressed forward by springs, c c, 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, c squared, 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 glass, a fact abundantly demonstrated by Mr. Woodbury in his experiments on the Photo-Filigrane process, and confirmed by some trials which we have made.

It must be confessed that roller slide experiments which we have made with sensitive films supported on gelatine sheets, or on such composite sheets as the alternate rubber and collodion pellicle of Mr. Warnerke, have been hardly satisfactory—­possibly, however, from our own want of skill; while no form of the Calotype process which we have tried has proved so satisfactory as gelatino-bromide paper.—­Photo.  News.