652 



DEMONSTRATIONS OF NORMAL VISION 



[Cn. XV 



DEMONSTRATIONS REPRESENTING NORMAL AND DEFECTIVE 



VISION 



917. Source of light. For the most successful demonstrations 

 of vision and its refractive defects it is necessary to have a right- 

 angle arc lamp and a direct electric current. However, for all the 

 experiments except the one to show unequal refraction in the two 

 eyes, the other sources of light mentioned in this book can be used. 

 If the large sources are used it is desirable to have a shield with an 



, Condenser 



FIG. 



378. PROJECTION APAPRATUS WITH THREE-LENS CONDENSER 

 OPTICAL BENCH FOR DEMONSTRATIONS REPRESENTING VISION. 



Commencing at the left : 



W 1 W l Supply wire to the knife-switch and from the switch through the 

 rheostat to the upper or positive carbon of the arc lamp. 



W* W 2 Supply wire to the knife-switch, and from the switch to the lower 

 carbon of the arc lamp. 



L The source of light (crater of the upper carbon). 



Lamp Block The block for supporting the arc lamp and by which it can be 

 moved back and forth on the optical bench. 



Base Board The board on which are the tracks of the optical bench (see 



% 159)- 



1 Condenser* The triple-lens condenser. The second element of the con- 

 denser (2) should have a focus of 30 to 40 centimeters (12 to 15 inches). 



W The water-cell to absorb the radiant heat. 



Obj. The object (lantern slide of radial lines, etc., fig. 383-393). 



Lens The trial lens serving to project the image. 



Block i The block supporting the condenser and water-cell. 



Block 2 The block serving as a support for the lantern slide, and by means 

 of which the slide can be moved back and forth on the optical bench. 



Block j The block supporting the lens carrier, and by means of which the 

 lens can be moved back and forth on the optical bench. 



These experiments, with the accompanying explanation, have been com- 

 piled from lectures and demonstrations given by the senior author before the 

 Sixth District Branch of the Medical Society of the State of New York, 

 October, 1913; The Conference of Veterinarians at the New York State Vet- 

 erinary College, December, 1913; and before the Cornell University Summer 

 School, July, 1914. 



