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_. * * * * * INSTANTANEOUS PHOTO SHUTTER. M. Audra, in the name of M. Braun, of Angoulême, has presented to the Photo Society of France a new instantaneous shutter. The shutter is formed by a revolving metallic disk out of which a segment has been taken. This disk is placed in the center of the diaphragms, in order to obtain the greatest rapidity combined with the least possible distance to travel. On the axis to which this circular disk is fixed is a small wheel, to which is attached a piece of string, and when the disk is turned round for the exposure the string is wound round the wheel. If the string be pulled, naturally the disk will revolve back to its former position so much the more quickly the more violently the string is pulled. M. Braun has replaced the hand by a steel spring attached to the drum of the lens (Fig. 2) By shortening or lengthening the string, more or less rapid exposures may be obtained. [Illustration: AAA, lens; B, aperture of lens; C, metallic disk; D, wheel on the axis; E, cord or string; E¹E¹E¹E¹, knots in string; G, steel spring; H, catch; K, socket for catch.] * * * * * SULPHUROUS ACID.--EASY METHOD OF PREPARATION FOR PHOTOGRAPHIC PURPOSES. Within a short period sulphurous acid has become an important element in the preparation of an excellent pyro developer for gelatine plates; and as it is more or less unstable in its keeping qualities, some easy method of preparing a small quantity which shall have a uniform strength is desirable. A method recently described in the _Photographic News_ will afford the amateur photographer a ready way of preparing a small quantity of the acid. [Illustration]