NATURAL PHILOSOPHY. 205 



and screw on the back tight. The camera is thus light, tight, and properly 

 focussed ; and nothing remains to be done but to lower it to the bottom of 

 the sea. 



" Up to the present point everything has been done on land. "We now lash 

 the whole of the apparatus, properly set, to the stern of the boat, and, when 

 we arrive at the proper spot, sink the camera. By means of the lowering 

 rope we can find when the camera is upright at the bottom. When satisfied 

 on this point, we raise the shutter in front of the camera box, by means of the 

 string attached to it, and the other end of which communicates with the boat. 

 The camera is now in action. 



" The tune I allowed for my negative was ten minutes, and you will perceive 

 it is a weak one. It took some time to develope with three grains of pyro- 

 gallic acid to the ounce. 



"There are one or two points worthy of notice as having occurred in the 

 experiment. The first is, that the image is formed on the plate in its natural 

 position, and not inverted. From this it would appear that the piece of glass 

 in front of the camera box, and the water conjointly, act in the same way as 

 a parallel mirror. Another fact is, that the salt water does not materially 

 injure the plate. With all my care, the great pressure at the depth to which 

 I sunk my camera forced the water into the camera itself, and covered the 

 collodion plate. When I opened the camera and found it full of water, I 

 despaired of having obtained a view ; but it would appear that salt water is 

 not so injurious as I had feared. I took the precaution of washing the plate 

 gently with fresh water, and then of dipping it for an instant in the silver bath. 



"This application of photography may prove of incalculable benefit to science. 

 We may take (to a reasonable depth) sketches of submarine rocks, piers of 

 bridges, outlines of sand banks, in fact, everything that is required under 

 water. Should a pier of a bridge require to be examined, you have but to suit 

 your camera, and you will obtain a sketch of the pier, with any dilapidations ; 

 and the engineer will thus obtain far better information than he could from 

 any report made by a diver." 



On the Application of Photography to the Copying of Ancient Manuscripts, &c. 

 Dr. Diamond, of England, in a recent communication, states, that he has 

 turned his attention to this branch of the art for some years with perfect suc- 

 cess, and recommends the following treatment as the result of his experience : 

 An old mixture of collodion originally made sensitive with a compound of 

 iodide and bromide of ammonium is best ; but any old collodion is to be pre- 

 ferred to newly mixed. A light object (such as the page of an ordinary book), 

 half size, if a single lens is used with an ordinary diaphragm, is to be exposed 

 about three minutes; full size, 12 or 15 minutes; a double combination lens 

 takes only hah" the time, but should be much stopped with a diaphragm. The 

 picture is to be developed as usual with a weak solution of pyrogallic acid 

 freely dashed over the surface. After cleaning the picture perfectly from the 

 hypo, a mixture should be passed over it composed of 2 drachms of bichloride 

 of mercury and 2 drachms of chloride of ammonium dissolved in 10 oz. of 

 common water. The picture now assumes a bluish tint. Wash it quickly and 

 thoroughly, and pour over it at once a solution of hyposulphite of soda, five 



