THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JANUARY 1859. 



I. On the Camera Obscura. By Prof. Petzval of Vienna"^-. 



ON the 23rd of July, 1857, Prof. Petzval presented his new 

 object-glass to the Academy of Vienna, and at the same 

 time made a communication on the general properties of the 

 camera obscura, which, from its elementary character, is well 

 adapted to supply photographers with much accurate and valu- 

 able information. A somewhat complete abstract of this com- 

 munication, therefore, cannot fail to interest a large number of 

 readers. 



A camera obscura may be defined as an instrument for obtain- 

 ing, at a finite distance, an image of any number of objects ; and 

 in accordance with this definition, numerous properties at once 

 suggest themselves as desirable. It will be well, in the first 

 place, to enumerate the properties which may be reasonably 

 demanded, in order subsequently to examine how far such de- 

 mands can be satisfied. 



We may reasonably demand that the image shall be well de- 

 fined or sharp, that it shall also be well illuminated so as to 

 exhibit proper light and shade; further, that it shall be true to 

 nature, and also that it shall lie in a plane. If possible, too, 

 the camera should simultaneously furnish images of both near 

 and distant objects, should possess a large field of view, and give 

 at pleasure either large or small pictures. Lastly, the instru- 

 ment must have a convenient form, and cost as little as possible. 



Most of these desiderata exist in an arrangement wherein 

 the optician's art is quite dispensable. If a screen be placed 



* For the report, of which au abstract is here given, see Sitzungsherichte 

 der tnathem. naturw, Classe der kaiserlichen Academic der Wissenschnftcn, 

 vol. xxvi. p. 33. 



Phil. Ma(j. S. 4. Vol. 17. No. 111. Jan. 1859. B 



