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g4 ^ REPORT — 1861, 



Imagine, in tlie first place, a tliick spherical shell of glass, having its internal 

 spherical cavity filled with water ; and then, since the entii-e sphere is not required, 

 imagine a central zone of the glass shell removed, and its place supplied by the 

 J)rass mounting of the lens. 



. Wheji the above arrangement is iitted with a central diaphragm having a small 

 centi'al apertm-e, it is evident that the pencils of light which pass through it must 

 be incident peroendicularly upon each of the four smfaces; therefore there is 

 no such thing m this lens as an oblique pencil, the errors due to oblique in- 

 cidence are completely avoided, and the image foiiued in eveiy part by direct 

 pencils. 



The glass shell, being a lens with concentric surfaces, acts as a concave or 

 diminishing lens, and has positive focal length ; while the eenti'al sphere of water 

 acts as a convex lens, and has negative focal lenglh. The- medimn" haxdng the 

 highest refractive and dispersive power is therefore made iiito a concave lens, while 

 the medium having the loivest refi^activ* and dispersive power, is made into a 

 convex lens. It is possible therefore to render thia compound achromatic by giving 

 a suitable radius to the inner giu-face of the shell, The investigation is extremely 

 simple, and the practical result very neat and convehient. It tmiis out that when 

 light flint-glass is used, the lens is achromatic when the inner radius of the shell is 

 about one-half the length of the outer radius. The combination may properly be 

 called a symmetrically achromatized sphere. It is a valuable property of a sphere 

 achromatized in this way, that its focal length is greatly increased, so that a large 

 picture can be taken with a tolerably small lens. 



The central diaphragm is another curious part of this instrument. It is evident 

 that if it were merely famished with a central circular hole, the sides of the picture 

 would be less illuminated than the centre. To meet this inconvenience the cen- 

 tral hole is made elliptical, and in front of it are placed two upright thin partitions, 

 radiating from the centre, and looking like the open wings of a butterfly. These 

 stop some of the light of the central pencil and make it cylindrical, and at the same 

 time they make the side pencils cylindrical also, and of the same diameter as 

 the eenti'al one. This simple contrivance answers perfectly ia equalizing the illu- 

 mination. 



The image of distant objects, formed by a panoramic lens, lies upon the surface 

 of a sphere which is concentric -ndth the lens. But the objects of an ordinary view 

 are not all distant ones, for the objects upon the gTOund are generally much nearer 

 to the lens than those upon the horizontal line. It is found, therefore, that the best 

 form of focusing-screen to meet the majority of cases which occur in practice, is 

 a part of a cylinder having the same centre a^ the lens, and including about 30° 

 below and 20° above the horizontal line. The panoramic picture therefore includes 

 about 100° in width and 50° in height. The iipright lines are straight, and 

 the perspective strictl}^ correct in all parts of the picture. 



Collodion pictiu'es are taken upon cui-ved glasses, and the negatives printed in a 

 curved printing-frame. The author has not found gi-eater practical difliculty in 

 working upon curved than upon flat glasses. 



A complete set of Panoramic Apparatus, manufactured by Mr. Thos. Ross, and 

 also a negative upon a curved glass, including about 100°, and a print from the same, 

 were sent for inspection. 



Microscopic Observations on the Structure of Metals. By H. H. Yivian, 



It is well known that silver and malleable iron, when newly broken, give a very 

 considerable reflexion of light fi'Om the fi-actm'e, and it has generally been under- 

 stood that the struetm'e was gi'anular, or composed of trystals, and that the re- 

 flexion of light was from their angles. On examining specimens of the above-named 

 metals with a microscope, however, the structm-e was discovered to be perfectly 

 porous or cellular, and the reflexion of light seen was from the inner surfaces of 

 the cells, which, though minute, were most brilliantly reflecting, especially when 

 newlj^ broken ; and when the metal was bent a little in one direction before break- 

 ing, thereby presenting the sides of the cells to the proper angle, the reflexion was 

 more fully seen than when the cells remained in their natural position. There is a 



