Chemistry and Physics. 



401 



persons at once. The author considers in the present paper only the phe- 

 nomena which are seen with a lattice composed of numerous parallel 

 openings. The one employed by him had 1440 parallel lines upon a 

 plane glass 54 mm - by 13 mm . The spectrum obtained by this lattice could 

 be projected upon a trough filled with a fluorescent liquid, upon paper 

 impregnated with such a liquid, upon a ruler of uranium-glass or upon 

 photographic paper. The spectrum as projected upon a common paper 

 screen exhibited between the two spectra of the first order toward the 

 centre and between the two lines H in the violet, an ill defined dark space. 

 When fluorescent paper was made to receive the spectrum, this dark 

 space became at once sharply defined. The spectrum was longer upon 

 chinin-paper than upon the other fluorescent substances which the author 

 tried, and he confined himself to this in his investigation. The author gives 

 a mathematical investigation of the spectrum as produced by parallel open- 

 ings, and then makes with the compasses upon the fluorescent paper the 

 requisite measurements of the distances of the points where the first 

 bright spectrum of the diffracted light commences. The wave length is 

 then given by the formula l=ze sin y>, in which e represents the distance 

 between two successive lattice-openings and V the angle which the dif- 

 fracted ray makes with the normal to the surface of the lattice. By 

 placing a violet-colored glass over the opening near the heliostat, the 

 most refrangible end of the spectrum became visible with still greater 

 distinctness and exhibited the sharpest termination : even on common 

 paper the spectrum could be seen and with exactly the same length. 

 When the spectrum as thus produced was received upon a plate of por- 

 celain, no trace of extension could be remarked ; the spectrum terminated 

 with the extreme visible rays. The author found as the results of his 

 measurements the following wave lengths in fractions of a millimeter. 



Extreme visible red rays ^ = 0-0007064. 



Extreme visible violet rays ^ — 00003956. 



Most refrangible invisible jays A — 0 , 0003540. 

 Hence it appears that light from the extreme red to the extreme invisible 

 ray embraces a complete octave. 



With the view of confirming this result the author produced upon 

 chinin-paper a spectrum by means of the same object-glass and a Munich 

 flint glass prism of 45° at a distance of 1 meters. In this manner many 

 of Fraunhofer's and Stokes's lines were seen with great distinctness. The 

 distances of these lines were measured from the line B, and laid off as 

 ordinates upon an axis of abscissas upon which the single distances of 

 the ordinates are expressed by the difference of the corresponding wave 

 lengths. In this manner the author obtained a curve which from the line 

 H to the extreme invisible ray appears to follow the same law as the other 

 portions of the spectrum. Eisenlohr has furthermore found that crown 

 glass does not absorb the invisible rays in such a manner as to shorten 

 the spectrum. This effect is produced by the low dispersive power of the 

 glass for the invisible rays. This is shewn by the fact that a plate of 

 crown glass placed so that the rays constituting the interference spectrum 

 should pass through it before falling upon the chinin-paper does not pro- 

 duce any shortening of the spectrum. By piercing a hole in the screen 

 upon which the spectrum was received where the invisible rays fell the 



SECOND SERIES, VOL. XXII, NO. 66. — NOV., 1856. 



51 



