202 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



inch across, and mounted generally in cork frames for con- 

 venient handling and preservation, and beautifully illustrate 

 the dependence of the form of the colored fringes on the 

 external shape of the glass. Price, set of five, $8.00. 



" ten, $15.00. 



If two unannealed rect- 

 angular pieces of glass are 

 crossed at right angles the 

 structure of the fringes will 

 be varied in a similar man- 

 ner to those represented in 

 the drawing annexed. 



Price, $2.50. 



Oxy-Hydro Polar- 

 iscope. (Fig. 730.) 

 This is an apparatus 

 to show the phenome- 

 na of polarization of 

 light to a number of 

 persons at once. The 

 name implies that the 

 light decomposed is 

 produced by the unit- 

 ed effect of burning the two gases named. The burning gas 

 is thrown upon lime, exactly as shown under oxy-hydro mi- 

 croscope. The polarizing apparatus is in principle what has 

 been already described, but having magnifying lenses at- 

 tached, it is capable of being thrown upon an extended 

 screen at a distance. Suppose A A to be screwed on to the 

 front of a magic lantern, or oxy-hydrogen microscope box, 

 instead of the usual nozzle the light would pass through 

 the two lenses, B and c, and be reflected from and polarized 

 at D, which is a bundle of glass plates. Passing along the 

 tube, it is again reflected at G ; another bundle of glass 

 plates, previously, however, passing through the lenses 

 under F. Finally it is thrown on to a screen from G. Into 

 the hole, E, is placed the film of crystal, from which the 

 colors are to be thrown. 



