[ 357 ] 



XL VI. On a new Optical Saccharometer. By the Rev. John H. 

 Jellett, M.A., Fellow of Trinity College, and Professor of 

 Natural Philosophy in the University of Dublin*. 



THE instrument, of which the following is a description, is 

 represented in the annexed woodcut, fig. 1. a a is a short 

 tube, containing two large lenses, serving to* condense the light 



Fig. 1. 



of a lamp, which is placed as nearly as possible in the principal 

 focus of the lower lens, b b, c c is a short tube carrying at one 

 extremity a lens, c c, and at the other extremity a diaphragm, 

 bb, pierced at its centre by a very small hole which is situ- 

 ated in the principal focus of the lens c c, and also, when the in- 

 strument is adjusted, in the principal focus of the upper lens a. 

 By this arrangement a beam of light is obtained emerging from 

 c c sensibly parallel to the axis of the tubes. This beam is po- 

 larized by being transmitted through a NicoPs prism contained 

 in the tube dd. ee is a vessel pierced at the lower end by a 



* Communicated by the Author, having been read before the Royal Irish 

 Academy, January 26, 1863. 



