NATURAL rniLOSOPIIT. 141 



NEW MICROSCOPE. 



In a letter from M. Moigno, in the "Journal of the Franklin 

 Institute " for August, 18G8, is described a novel and ingenious 

 microscope, invented by M. Caselli, of Rome. It consists of a 

 magnifier, one of whose sides is silvered l)y precii/itatlon with the 

 aid of organic sulistances. If an object be placed in front of this 

 lens, at a proper distance, a well-magnified virtual image is ob- 

 tained. Two convergences and one divergence contribute to 

 produce the magnifying power: 1. The convergence of the ra3's 

 entering the lens. 2. The divergence of these rays by the silver 

 concave mirror at the back. 3. The convergence of these rays on 

 quitting the upper surface of the lens. 



The mirror-lens is placed horizontally, or slightly inclined, so 

 as to keep at a distance the image of the object. Above it, and 

 fastened to the same pillar, is the horizontal diaphragm on which 

 the object is placed ; this is furnished with a screw and rack-work, 

 so as to be raised or lowered at will. Above this, at a short dis- 

 tance, is placed a screen of white or almost colorless card-board, at 

 at angle of 45°, and pierced exactly over the centre of the mirror- 

 lens with a small hole, through which the image is seen. This card 

 also serves to reflect light on the mirror-lens, and to make the 

 image appear on a white ground. With this microscope there is 

 no need of the usual lenses or mirror to light up the object, since 

 the mirror-ieus itself causes the light to converge on the object. 



NATURE OF THE PHOTOGRAPHIC IMAGE. 



Dr. E. Reynolds recently read a paper, giving some curious 

 results on the action of ozone on sensitive photographic plates, be- 

 fore the Dublin Chemical and Philosophical Club. He found that 

 the undeveloped image upon a sensitized plate after exposure in 

 the camera, subjected to the action of ozone, was completely ob- 

 literated, so that a new image might be taken upon it. This fact, 

 he remarked, proved that the production of an image was due to 

 a chemical action, and thus overthrows the mechanical theory of 

 photographic images. The ozone in his experiments was obtained 

 sometimes by the aid of elcctricit3% and sometimes by the action 

 of air upon phosphorus. — Journal of the Franklin Institute. 



GLYPHOGRAPHY. 



A polished plate of copper, such as is usually employed by 

 engravers, is blackened by being washed over with sulphide of 

 potassium, sulphide of ammonium, chloride of platinum, or other 

 means. The plate is then washed and dried, and is evenly coated 

 with a mixture of wax, resin, and suljihate of lead, the thickness 

 of the coating not exceeding a thirtieth of an inch. This coating 

 is white and smooth, and the plate when thus prepared is ready 

 for being sketched upon, or for being photographed upon. 



