496 



Capt. W. de W. Abney. Examination for [May 14. 



E is a small tube for the eye to look down into a box 4 feet lonj 

 G is an aperture in the side of the box covered with ground glass ; L 

 is a gas-light ; A rotating sectors which can be opened and closed at 

 will ; M a mirror to reflect the light on to a card (which can be 

 changed at will, and on which are one or more black spots) slipping 

 into a slot S from the top of the box. E is so arranged that the whole 

 of the card can be viewed. The observer places his eye at E, and the 

 sectors, whicb at first are closed, are gradually opened until the 

 observer can see that there are black spots on a white ground. The 

 angle of the aperture of the sector is noted. Each eye is tested. 



In this case my own right eye, agreeing with that of Mr. Nettle- 

 ship, was used as the standard, since it was with that that the normal 

 luminosity curve was originally made. 



From this it may be concluded that C.'s appreciation of light to the 

 standard is about half for the right eye, and two-thirds for the left that 

 of the standard. 



The horizontal colour field was tested by a modification of the colour 

 patch apparatus. 



FIG. 3. 



A brass-work frame was made as shown, fig. 3. A and B are fixed 

 to a board, the other arms are capable of moving with parallel motion, 

 the arm BD slides through D ; at B, and attached to BD, is a mirror 

 which can be fixed in any position. The light, when once turned in 



