It is from a failure to observe this precaution that so many of the shadow pictures show blurred outlines. It is with these pictures as with a shadow of the hand thrown on the wall--the nearer the hand is to the wall, the more distinct becomes the shadow; and this consideration makes Professor Wright doubt whether it will be possible, with the present facilities, to get clearly cut shadow images of very thick objects, or in cases where the pictures are taken through a thick board or other obstacle. The Röntgen rays will doubtless traverse the board, and shadows will be formed upon the plate, but there will be an uncertainty or dimness of outline that will render the results unsatisfactory. It is for this reason that Professor Wright has taken most of his shadow pictures through only the thickness of ebonite in his plate-holder. A most successful shadow picture taken by Professor Wright in this way, shows five objects laid side by side on a large plate--a saw, a case of pocket tools in their cover, a pocket lense opened out as for use, a pair of eye-glasses inside their leather case, and an awl. As will be seen from the accompanying reproduction of this picture, all the objects are photographed with remarkable distinctness, the leather case of the eye-glasses being almost transparent, the wood of the handles of the awl and saw being a little less so, while the glass in the eye-glasses is less transparent than either. In the case of the awl and the saw, the iron stem of the tool shows plainly inside the wooden handle. This photograph is similar to a dozen that have been taken by Professor Wright with equal success. The exposure here was fifty-five minutes. A more remarkable picture is one taken in the same way, but with a somewhat longer exposure--of a rabbit laid upon the ebonite plate, and so successfully pierced with the Röntgen rays that not only the bones of the body show plainly, but also the six grains of shot with which the animal was killed. The bones of the fore legs show with beautiful distinctness inside the shadowy flesh, while a closer inspection makes visible the ribs, the cartilages of the ear, and a lighter region in the centre of the body, which marks the location of the heart.