VIII. EDUCATIONAL. 245 



964. Tour simple Models, for instruction in the use of the 



telescope and the microscope. 



J. WilJielm Albert, Fr ankf or t-on- Maine. 



The four models for optical instruction are open instruments with lenses 

 and shades. They show the course of the rays and illustrate in a simple 

 manner the Galilean, astronomical, and terrestrial telescopes, and the com- 

 pound microscope. 



These models are largely used in German and foreign educational insti- 

 tutions. 



964a. Sciopticon and three Manuals. 



W. B. Woodbury. 



965. Coloured Chalks for lectures, with a Black Board. 



C. Blattner, Munich. 



966. Interference Apparatus by Fresnel, executed for edu- 

 cational purposes by Ch. Jung, Giessen. 



Physical Collection of the University of Giessen, Prof. 



Buff. 



918. Apparatus for demonstrating the Refraction of 

 Light in liquids, according to J. Miiller. 



J. Wilhelm Albert, Frankf or t~on- Maine. 



The semicircular plate of the refraction apparatus is of glass, ground 

 on its outside and having the scale burnt into it in black. The ray refracted 

 from the liquid appears therefore on the outside of the graduated plate and 

 can thus be viewed by large audiences. 



967. Educational Apparatus, for elementary experiments 

 on Refraction. Prof. Dr. J. J. Oppel, Fr ankf or t-on- Maine. 



This apparatus is only a modification of the old experiment of viewing 

 a coin at the bottom of a basin full of water. The coin is replaced by a white 

 line upon black ground, and the water by a movable cube of glass. The 

 position of the eye is fixed^by a dioptric plate. 



968. Educational Apparatus for illustrating astronomical 

 refraction and its effect on measured heights of stars. 



Prof. Dr. J. J. Oppel, Fr ankf ort-on- Maine. 



The eye looks through a dioptric plate over a wooden globe (" earth ") 

 towards a few stars and the rising moon, which appears above or below the 

 horizon, according as the piece of glass, which represents the refracting 

 atmosphere, is lifted up or removed by means of a contrivance attached to it. 



969. Two Colour-tables, for illustrating " colour blindness/ 1 

 with greenish glass (absorbing the ends of the spectrum) belonging 

 to them. P ro f- D T - J J- Oppel, Franhfort-on- Maine. 



Both tables, each with 10-12 colour-couples upon black ground, have 

 reference to the most frequent form of achromatopsy, the so-called red, and 

 green, blindness. The one table contains colour-couples which are most 

 generally mistaken for one another ; the other those that are never mistaken. 

 The green glass, added to the tables, enables a normal eye to get an idea of 

 that peculiarity of vision. 



