202 ANNUAL OF SCIENTIFIC DISCOVERY. 



mode of making use of the phototype consists in casting a magnified copy 

 of a sun portrait on canvas for the aid of .portrait-painters, who thus sketch 

 from Nature's sketches. In a recent sitting of the Soci6te d' Encouragement 

 pour {'Industrie Nationale, at Paris, according to Galignani, it was stated 

 that a photolithographic process, which has so long been desired, has at 

 length been discovered. It was thus described : An ordinary lithographic 

 stone is taken, and a solution of bitume de Jnd&e (Jew's pitch) is placed on 

 it. A negative photographic proof is then put on it, and is pressed on the 

 stone for a period which may vary from ten minutes to four or five hours. 

 The page is then washed in pure ether, which soon evaporates. The figure 

 is then found properly marked with its lights and shades, and it may be 

 inked and drawn off as in ordinary lithographs. 



During the past summer in the Baltic, the British steamers employed in 

 examining the enemy's coasts and fortifications took photographic views 

 for reference and minute examination. With the steamer moving at the 

 rate of fifteen knots an hour, the most perfect definitions of coasts and bat- 

 teries were obtained. Outlines of the coasts, correct in height and in dis- 

 tance, have been faithfully transcribed ; and all details of the fortresses 

 passed under review of -the photograph are accurately recorded. 



At the Royal Greenwich Observatory, the beautiful system of register- 

 ing magiietical and meterological changes, by means of photography, con- 

 tinues to be employed, and efforts have been made to "multiply copies of 

 the Photographic Registers. After many experiments, it was found that, 

 by the agency of sunlight upon the back of an original photograph, whose 

 face was pressed closely, by means of a glass plate, upon proper photo- 

 graphic paper below, there would be no difficulty in preparing negative 

 and inverted secondaries, and, from them, positive tertiaries. Thus, be- 

 yond the trouble which the process involves, Mr. Airy anticipates that it 

 will be easy to multiply copies to any extent which may be desired. 



The photographic apparatus in use at the Royal Observatory, for taking 

 magnetic observations, is constructed as follows : Each magnetic bar is 

 made to carry a little mirror, which reflects the light of a lamp upon a 

 piece of photographic paper, kept constantly moving behind an opaque 

 plate, having but one small vertical opening. On this, for every minute 

 of the twenty-four hours, each vibration of the needle is faithfully recorded. 

 The chemical radiations of an Argand lamp supply the observer's place ; 

 and at the same time that it records every change in the phenomenon of 

 terrestrial magnetism, it is made to mark the most delicate alterations in 

 atmospheric pressure, and to note every increase or diminution of temper- 

 ature. At Greenwich, the magnets, the barometers, and the thermome- 

 ters are all registered by the chemical power of light ; and MM. Faye and 

 Gonjon, at Paris, knowing the error of the human eye in observations on 

 a bright object, have substituted the daguerreotype plate for the purpose 

 of ascertaining the actual diameter of the sun, and they propose to the 

 principal observatories of Europe to determine, by a similar method, the 

 absolute time. 



