250 SEC. 7. LIGHT. 



979; Trepiscope. An optical apparatus made by the late 

 Richard Roberts, C.E., of Manchester, and first shown at the 

 meeting of the British Association at Dublin in 1835. 



The Committee, Royal Museum., Peel Park, Salford. 



On being turned by hand or by power the card on the disc is caused 

 to revolve from 6,000 to 40,000 times a minute; on viewing the re- 

 volving disc through the eye-kole, the printing on the card can be read with 

 ease and distinctness. 



The time given for one view of the card may not exceed the 150,000th of 

 a second when the disc is revolving at the highest speed. 



980. Radiograph. 



The Committee, Royal Museum, Peel Park, Salford. 



A small apparatus to show that the spokes may be counted whilst the wheels 

 revolve at a very high velocity. Invented by the late Richard Roberts, C.E., 

 of Manchester. 



979a. Phosphoroscope, by Becquerel.. 



M. J. Duboscq, Paris. 



979b. Phosphorescent Tubes, set in the form of writing. 

 These tubes preserve their brilliancy in the darkness long after 

 being exposed to solar light. Alvergniat Freres, Paris. 



981. Newtonian Disc, for rotating movement transmitted by 

 caoutchouc bands. Luizard, Paris. 



981a. Newton's Apparatus. M. Lutz, Paris. 



983. Pair of Reflectors, for the demonstration of the laws 

 of reflection. Elliott Brothers. 



983a. Reflector of 22 mm. diameter, for Foucault's telescope. 



M. Lutz, Paris. 



983b. Apparatus illustrating Persistency of Vision. 



S. F. Pichler. 



983c. Magic Mirror. Robert von Tarnow. 



This mirror is a curiosity, and consists of a brass concave disc with finely 

 polished surface. At the reverse rough side there are several Arabic charac- 

 ters in relief. By exposing the polished surface to the rays of the sun in such 

 a way that they reflect them on the wall, the Arabic figures of the reverse 

 side of the disc become plainly visible in the reflected light on the wall. 



983c. Selenium Eye* C. W. Siemens, F.R.S. 



994. Government Safety Magazine Lamp. 



J. Gardner Sf Sons. 



Constructed at the request of the Home Office. The aim was to invent a 

 lamp which would burn in a powder magazine and other dangerous places in 

 perfect safety, and would exclude the powder which, it is well known, is found 



