974 SEC. 18. BIOLOGY. 



19. Tympanum and lever recording instrument. 



20. Haemodromograph, by Chauveau. 



21. Portable electric chronograph, giving 100 double vibrations 

 per second. 



22. Tambours conjugues, for reproducing movements at a 

 distance. 



23. Pantograph of transmission, for reproducing movements at 

 a distance. (See opposite.) 



7. For demonstrating the laws of vision : 



Large glass model of human eye ; stereoscope and geo- 

 metrical slides, to show effect of binocular vision. 



