In our former articles we have spoken principally of stereoscopic pictures. These are still our chief favorites for scenery, for architectural objects, for almost everything but portraits,--and even these last acquire a reality in the stereoscope which they can get in no other way. In this third photographic excursion we must only touch briefly upon the stereograph. Yet we have something to add to what we said before on this topic. One of the most interesting accessions to our collection is a series of twelve views, on glass, of scenes and objects in California, sent us with unprovoked liberality by the artist, Mr. Watkins. As specimens of art they are admirable, and some of the subjects are among the most interesting to be found in the whole realm of Nature. Thus, the great tree, the "Grizzly Giant," of Mariposa, is shown in two admirable views; the mighty precipice of El Capitan, more than three thousand feet in precipitous height,--the three conical hill-tops of Yo Semite, taken, not as they soar into the atmosphere, but as they are reflected in the calm waters below,--these and others are shown, clear, yet soft, vigorous in the foreground, delicately distinct in the distance, in a perfection of art which compares with the finest European work. The "London Stereoscopic Company" has produced some very beautiful paper stereographs, very dear, but worth their cost, of the Great Exhibition. There is one view, which we are fortunate enough to possess, that is a marvel of living detail,--one of the series showing the opening ceremonies. The picture gives principally the musicians. By careful counting, we find there are _six hundred faces to the square inch_ in the more crowded portion of the scene which the view embraces,--a part occupied by the female singers. These singers are all clad in white, and packed with great compression of crinoline,--if that, indeed, were worn on the occasion. Mere points as their faces seem to the naked eye, the stereoscope, and still more a strong magnifier, shows them with their mouths all open as they join in the chorus, and with such distinctness that some of them might readily be recognized by those familiar with their aspect. This, it is to be remembered, is not a reduced stereograph for the microscope, but a common one, taken as we see them taken constantly. We find in the same series several very good views of Gibson's famous colored "Venus," a lady with a pleasant face and a very pretty pair of shoulders. But the grand "Cleopatra" of our countryman, Mr. Story, of which we have heard so much, was not to be had,--why not we cannot say, for a stereograph of it would have had an immense success in America, and doubtless everywhere.