By Professor O.N. ROOD.

ABOUT a year ago there was considerable excitement in the photographic world on the subject of sharp paper prints, and many articles on the subject appeared in the English and American journals. The prevailing opinion, as I recollect, was much to the effect that want of this quality resulted mainly from the photographic image sinking into the paper, and that if it could only be confined to the surface the much-desired result would be attained

At that time I made a considerable number of experiments on the subject, and ascertained (as I suppose) the main elements on which this quality depends. In the first place, plain photographic paper was variously and heavily sized, so as to prevent the albumen from sinking in: in some cases the paper received coat after coat of plain collodion, or of spirit varnish, &c. In preventing the albumen and silver image from sinking in I was eminently successful-so much so that the albumen, image and all, could often be peeled off in patches from the finished but wet print! But by all these expedients the sharpness was not at all improved; and even the film of albumen peeled from the paper, when examined under the compound microscope, showed an image not at all sharper than common.

A microscopic examination of a number of common but, good albumen prints was then made; and I was much struck by the fact that minute portions of them, here and there, were wonderfully sharp, though the print, taken as a whole, might be quite poor. The surface seemed to consist of little hills and valleys, the printing being sharp only on the tops of the hills, where the paper was in actual contact with the negative.

I then procured some thin and very smooth letter-paper, and albumenised it myself. This at once gave prints of a sharpness that I have never seen equalled. For example, I made a. minute negative of a page of Silliman's Journal the size of the original being 7¼ by 4 inches, and that of the negative 4/10 by 2/10 of an inch. The exterior portions of the plate were then cut away, so that the pressure might be concentrated on a small surface, and prints were made under the pressure of two spring clothes-clips. With the naked eye, or under low-power hand lens, nothing could be made out; but these prints, when placed under the compound microscope, a power of thirty diameters being used, showed the words, letters, and even the finer print, quite complete and astonishingly sharp. Some letters and portions of letters would have borne a much higher power. At that time I sent copies to Professors Norton and Silliman, in New Haven, though now I have neither prints nor the negative. Experiments were then made on common albumenised paper. Just before it went into the printing-frame it was subjected to strong pressure under a polished silver plate to render the surface smooth. The improvement was not marked. One of these latter prints I have still on hand, and, send to the Editor of this Journal.* It will be seen under the microscope that single letters, and even words; can be made out here and there; but it is vastly inferior to the others (this inferiority, indeed, being the reason of its remaining so long in my possession).

The letter-paper did not tone well: it was always spotted, more or less, so I discontinued its use.

It will be observed then, that this success--which I suppose is at least as great as that which the most aspiring photographer hopes to achieve--was reached solely by the use of a sharp negative, thin and exceedingly smooth paper, and more than ordinary pressure in printing--the image being allowed to sink in as far and as deep as it could, for the paper was sensitised by being immersed fifteen minutes in a. bath composed of nitrate of silver, water, and alcohol.

* We have examined the specimen under a power of forty diameters, when the grain of the paper appears painfully offensive, but can only decipher two letters, viz., a capital D and a C, though it is apparent enough that the photograph is a copy of a printed page.--ED.