148 ANNUAL OF SCIENTIFIC DISCOVERY. 



rapidity. 6. By comparison of these with other results obtained by 

 Prof. Wheatstone, it is sho\vn that the apparent brightness of the 

 electric spark is only one ten thousandth of what it would become if 

 the duration of the spark conld be prolonged to one tenth of a second. 

 These results were obtained by means of an instrument called a sela- 

 omctcr, the invention of Mr. Swan. In a later communication made 

 to the British Association, Mr. Swan applies these results to deter- 

 mine the limits of the velocity of revolving light-house apparatus. 



SOLAIl AND STELLAR DAGUERREOTYPES. 



IN the Comptes Rendus for June 3, M. Niepce furnishes a commu- 

 nication relative to some images of the sun, obtained by him through 

 the agency of the photographic art. The pictures were taken upon 

 glass prepared with albumen. A plate exposed five seconds showed 

 a very visible and distinct image, of a deep blood-red color, much 

 deeper in the middle than at the edges. A second plate, exposed ten 

 seconds, presented the same difference between the centre and the 

 circumference, but with greater intensity ; in addition, it had a circle 

 beyond the image in the form of a glory. These experiments seem to 

 confirm the opinion expressed by Arago, that the photogenic rays 

 emanating from the centre of the sun have more action than those near 

 the edge or circumference. 



Mr. Bond of the Cambridge Observatory has recently succeeded in 

 obtaining a Daguerreotype picture of the star alpha Lync in the space 

 of about 30 seconds, the image being transmitted through the great 

 refractor, used without the eye-glass. The picture is quite distinct, 

 and about the size of a pin's head. Mr. Bond, in announcing the fact, 

 says: "The question will doubtless occur, To what good purpose 

 can this discovery be applied? One of the first direct applications of 

 it would be the measurement of the angles of opposition and distance 

 of double stars. It is interesting to be assured of the fact, that the 

 light emanating from the stars possesses the requisite chemical proper- 

 ties to produce effects similar to certain of the solar rays, and that 

 these properties retain their efficacy after traversing the vast distance 

 which separates us from stellar regions. Of this distance some idea 

 may possibly be formed, if we can imagine a plain of two hundred 

 millions of miles in extent, at the distance of the star alpha Lyra, and 

 favorably presented to a spectator situated on the earth, appearing as 

 a mere point, only measurable by the aid of an excellent telescope, 

 furnished for an accurate micrometer ; or that light, moving at the 

 rate of 190,000 miles in a second of time, would require more thar 

 twenty years to traverse the intervening space. Yet such are the 

 facts, and it follows that the ray of light which made the first impres- 

 sion on our Daguerreotype plates took its departure from the stai 

 more than twenty years ago, long before Daguerre had conceived his 

 invention. 



" Our experiments have also a bearing upon the nature of the light 

 emitted from the stars. The images which 'we have thus far ob- 

 tained are quiu decided, having pretty distinct nuclei, although elou- 



