210 SEC. 7. LIGHT. 



that of any lesser number of prisms at pleasure. The instrument is fitted 

 with a new reflecting bright line micrometer ; when measuring with this 

 contrivance no light is visible in the field of view, but the wires of the 

 micrometer are seen faintly illuminated. 



830. Universal Spectroscope, with Browning's automatic 

 action, giving a dispersive power of from 2 to 12 prisms. 



John Browning, 



791. Rotating Tube Holder, a contrivance for containing 

 a number of Ffliicker's tubes, and obtaining their spectra suc- 

 cessively without loss of time. John Browning. 



792. Rotating Metal Holder, suggested by Mr. Lockyer, 

 for holding specimens of all the principal metals, and obtaining 

 their spectra successively, or for the purposes of comparison. 



John Browning. 



831. Direct-vision Spectroscope, with apparatus for 

 registering observations. 



Geneva Association for the Construction of Scientific In- 

 struments. 



This direct-vision spectroscope is distinguished from others of the same 

 description, in that the distance of the lines of the spectrum is measured, not, 

 by the superposition of the spectrum upon an illuminated micrometric scale, 

 but by measuring the angle formed by the e}-epiece in moving the cross 

 wires of the telescope from one line to the other, and then comparing it with 

 that formed by the telescope when directed successively to two lines of known 

 distance. A tangent screw effects the angular displacement of the telescope ; 

 this screw is graduated on the head to read angular displacements of less 

 than 20 seconds. A recorder, formed of a movable pencil which acts upon 

 a counter, serves to make series of observations in the dark. The collimator 

 telescope possesses also an angular motion, which serves to bring any portion 

 whatever of the spectrum to the centre of the field of view. 



832. General Apparatus for Spectroscopy, Polari- 

 sation, Reflexion, Refraction, and for various experiments 

 in Fluorescence. 



Geneva Association for the Construction of Scientific In- 

 struments. 



This apparatus has been constructed with the object of carrying out, with 

 one and the same instrument, all, or nearly all, experiments in spectroscopy, 

 rotatory polarisation, reflection, and refraction. The divided circle is mov- 

 able around an axis, and serves to bring the rays of light at any angle upon 

 the eyepiece of the line of collimation. For experiments in spectroscopy, a 

 table of one, three, or six prisms may be set up. The prisms are raised above 

 the divided circle sufficiently to allow of their being heated from below if 

 required. For determination of the line of collimation suitable arrangements 

 have been provided, and for experiments in polarisation, eyepieces fitted with 

 divided circles and nicols ; a Babinet compensator may also be adapted to them. 



The first apparatus of this kind was constructed for the use of Professor 

 Wiedernann, of the University of Leipzig. 



