178 SEC. 7. LIGHT.. 



* 



lenses, and a 7-inch meniscus, next to the source of light. The 

 last lens is made to slide backward and forward between guides, 

 so as to increase or diminish the cone of rays, and enable large or 

 small diagrams or pictures to be exhibited without material 

 distortion. Made and exhibited by Dr. Stone. 



823. Magnesium Lamp, provided with brass cylinders and 

 reflector. A. Herbst, Berlin. 



824. Brewster's Patent Kaleidoscope (with case). The 

 original form of the instrument made by Bate, of London, in the 

 year 1815. (Position of the reflectors capable of adjustment, 

 non-central eye piece, and rotating terminal disc, or box contain- 

 ing the coloured glass.) John Spiller, F.C.S. 



II. SELECTORS. 



a. SPECTROSCOPES, PRISMS, &c. 



825. Photographic and Spectrophotographic Speci- 

 mens and Apparatus of Sir John Herschel and Sir "William 

 Herschel. Prof. A. S. Herschel. 



1. Original fragments and complete photographs on glass with chloride of 

 silver of the forty foot telescope at Slough. Produced in 1839 by Sir John 

 Herschel, as a new modification of the process of Daguerre. Paper wrapper 

 of the specimens inscribed in autograph by Sir John Herschel with the above 

 description of the plates. 



2. Prismatic apparatus designed and used in researches on the photo- 

 graphic action of the different rays of the spectrum, by Sir John Herschel, 

 Slough, 1839. Original description, and notes qf experiments with the 

 instrument extracted from MS. journal. Specimens of photographed spectra 

 obtained with the instrument by Sir John Herschel, at Collingwood, in 1859. 



3. Heliostatic mirror (used by fixing outside to aperture in a window 

 shutter, and turning screws by hand inside to direct the sun's rays horizon- 

 tally or in a required direction). Glass prism to receive and bend downwards 

 the reflected ray to a table on which thermometers were exposed to action of 

 the different rays of its spectrum. Constructed and used (with other ap- 

 paratus not preserved) by Sir William Herschel, in experiments on thermal 

 radiation in the solar spectrum, described in the Philosophical Transactions, 

 1800-1801. 



A plate of light blue cobalt glass, mounted on cardboard diaphragm, pierced 

 with an eye-hole ; used with the prismatic photographing apparatus to exa- 

 mine test papers submitted to the solar spectrum (before sensitizing), and to 

 place a pencil mark or other datum line on the test paper in the exact position 

 of the yellow ray. When thus adjusted and fastened to the support, the sen- 

 sitive solution to be tested, if not already present in the paper, was applied to 

 its exposed surface with a brush, and the time of exposure and intensity of 

 the direct sunlight was at the same time recorded. Two small card-leaves 

 have, for the purpose of examination, been attached to the cardboard dia- 

 phragm, by closing which upon the glass, the " fiducial " yellow ray trans- 

 mitted by blue cobalt glass will be observed with the accompanying eye-piece 

 of a small pocket spectroscope placed with the plate, showing through the 



