148 



Paul Gebhardt. Berlin S. 



Acoustics: 



Stopped lipped pipe. 



Reed-pipe with reed striking upwards, funnel and 



glass window, stopped lipped pipe with divided 



sliding rod. 



Cagniard la Tour's Syren, with tachometer. (Fig. 2) 

 Tuning fork on sound-board. 



Telephones for demonstration or use, one of these 

 dissectable. 



Fig. 2. 



Optics: 



Simple goniometer (graduated arc and radial stop). 

 Glass prism, mounted on adjustable stand. 



Spectroscope with flint glass prism, comparison prism, slit, sighting 

 and scale telescope. 



Heliostat with clock-work. 



Model telescope for demonstration, with lenses and diaphragms in 

 skeleton frame. 



Newton's Coloured Rings Apparatus, in brass mount. 



Heat: 



Muschenbrock's Lever 

 Pyrometer (Fig. 3), 

 with 3 different metal 

 rods, for demonstrating 

 the expansion of metals 

 by heat. 



Sectional model of a 

 steam-engine cylin- 

 der and valve-gear. 



Fig. 3. 



