204: ANNUAL OF SCIENTIFIC DISCOVERY. 



first coated with Canada balsam ; at present the unmounted one and the one 

 protected by the balsam are unchanged, whereas the other has faded. 



A picture prepared in 1846 was so exposed that the lower part of it became 

 wet by rain ; at present the part so wetted has faded, while the rest of it 

 remains unaltered. Several pictures were prepared and mounted about ten 

 years ago, and kept in a dry room for about three years without any change, 

 after which they were placed in a very damp situation, and then faded 

 decidedly in a few months. 



IMPROVEMENTS IN PHOTOGRAPHY. 



Taking Photographic Images under Water. Mr. Penny, of England, pub- 

 lishes in the Journal of the Society of Arts, the following account of his expe- 

 rimental researches in taking photographic images under the surface of 

 water. 



A box, made as nearly water-tight as possible, is prepared large enough to 

 enclose the camera. This box is fitted, in part, with a piece of plate glass, 

 and on the outside is a wooden shutter, heavily leaded, and which is raised 

 by a string attached to it and communicating with a boat. 



On each side of the box is an iron band, terminating in a screw, and pro- 

 jecting beyond the back, which is loose, and fitted with an iron bar, having 

 a hole at each end, through which the screws of the band pass, and thus the 

 back is screwed down tight against the body of the camera by means of a 

 nut ; the inner surface of the back is padded, so as to make the camera box, 

 as far as possible, water-tight, when the back is screwed into its place. 



The box is fixed to an iron tripod, and a band, with an eye on its upper 

 margin, is passed round both camera, box, and stand ; to this eye is attached 

 the rope that lowers the camera to the sea bottom, and by which it is raised. 

 This is the whole of the apparatus employed. 



The first thing to be accomplished is to focus the camera, which process is 

 thus described by Mr. Penny: 



" The camera is placed in the box on the shore, and a view is focussed, 

 taking as the foreground an object at ten yards' distance. This I did with the 

 view now sent, but I fear it is too much. I then fix the stand by means of a 

 triangular wooden frame forced up between the legs of the tripod stand, and 

 which is prevented from slipping down by being attached to the top of the 

 tripod by a line ; this keeps the camera frame the exact distance from the 

 ground that it was when focussed on land, and the camera being focussed for 

 the same distance, it stands to reason that, provided the optical and chemical 

 properties are the same, we shall obtain a similarly good picture. 



" The next thing to be done is to prepare the plate and inclose it. The plate 

 is prepared with collodion, in the usual way, under the tent. It is then placed 

 in the camera (my camera used for this purpose takes a plate five inches by 

 four inches). I then take the camera to the box and stand, and throw a black 

 cloth over all. I examine the shutter in front of the camera box to see that 

 it is tight ; then, uncapping the camera under the cloth, I place it in the box, 

 and finally draw up the slide. I then push the camera completely into the 

 box, until the front of the lens presses against the plate glass front of the box, 





