A more simple plan, and one which will succeed when great delicacy is not required, consists in laying the sketch upon a sheet of Positive printing paper (a highly salted paper will be the best, as giving most intensity) and exposing to the light until a copy is obtained. All the details are faithfully rendered in this way, but it is sometimes difficult to obtain a Negative sufficiently black to yield a _vigorous_ print. SECTION IV. _Rules for taking Stereoscopic Photographs._ Binocular pictures of a large size, for the reflecting Stereoscope, may be taken with an ordinary View lens of about 15 inches focus. The ground glass of the Camera having been ruled with cross lines in the manner described at page 231, the position of some prominent object is marked upon one of the lines with a pencil, and the first view is taken. The stand is then moved laterally to the proper distance, and the Camera adjusted to its second position by shifting it until the marked object occupies the same place as before. The distance between the two positions should be about one foot when the foreground of the picture is twenty-five feet from the instrument, or four feet when it is at thirty or forty yards. But, as before shown at page 71, this rule is not to be followed implicitly, much depending upon the character of the picture and the effect desired. Photographs for the lenticular Stereoscope are taken with small lenses of about 4-1/2 inches focus. For portraits, a Camera may advantageously be fitted with two double-combination lenses, of 1-3/4 inches diameter, exactly equal in focal length and in rapidity of action. The caps are removed simultaneously, and the pictures impressed at the same instant. The centres of the lenses may be separated by three inches when the Camera is placed at about six feet from the sitter, or four inches when the distance is increased to eight feet. Pictures taken with a binocular Camera of this kind, require to be mounted in a reversed position to that which they occupy on the glass: for since the image of the Camera is _inverted_, when it is turned round and made erect, the right-hand picture will necessarily stand on the left side, and _vice versâ_. Mr. Latimer Clark has devised an arrangement for taking stereoscopic pictures with a single Camera, which is exceedingly ingenious. Its most important feature is a contrivance for rapidly moving the Camera in a lateral direction without disturbing the position of the image upon the ground glass. This will be understood by a reference to the following woodcut. [Illustration]