MISCELLANEOUS INSTRUMENTS. 



269 



Fig. 744. 



Dissected Cone. (Fig. 774.) The dissect- 

 ed cone is used for illustrating the conic 

 sections. It is formed of a cone of hard 

 wood cut in parts representing these sec- 

 tions, as the ellipse, parabola, hyperbola, 

 which may be put together by short pins in 

 the parts forming the complete cone. 



Price, $1.25. 



Hearing Trumpet, or Ear Trumpet. (Figs. 775 to 779.) 

 The hearing, or ear trumpet, is for the purpose of col- 

 lecting the rays of sound by reflection, and conveying them 

 to the ear. It may be considered as a reversed speaking 

 trumpet, with which it generally corresponds in form, 



Fig. 775. 



Fig. 776. 



though, for the sake of portability it is often curved ; they 

 are also recommended of a parabolic figure having the apex 

 of the paraboloid cut off, and the mouth of a small tube 

 inserted in the focus, to convey the sound concentrated at 

 that point to the auditory organ. Various other forms are 

 adopted in practice ; and of late, flexible India rubber tubes 

 formed over a spiral wire (Fig. 780) have been brought into 



