Related to Apparatus for investigating the role of eye movement in spatial perception illusions.
Description:

The notes and drawings (8 ff.) relate to the design and specification of the apparatus.

 

f.1: letter from F.N. Hales to H. Darwin. (see child of 'Notes')

 

f.2: set of calculations relating to required size of instrument for lens used.

 

f.3: initial sketch of instrument showing desired path of light rays from source, through a correcting lens and then a 'perforated plate', through a focusing lens, past a 'pendulum' and onto an (unidentified) surface.

A note pointing to the initial correcting lens reads: '? do we need this lens or will a milk glass plate do here?'

A crossed-through note below this in Hales' hand reads: 'The larger the perforated plate the better & if the m-glass behind it will do for source of light it might be made indefinitely large whereas if we will have lens behind it - that limits size seriously'

 

f.4: 'Dec. 15 1902.

Image say 3 1/4 x 4 1/4 perhaps a little more.

Length of exposure 0.1 sec to 1/4 sec.

Seconds pendulum.

Disc with holes in it 8" diam. or larger.'

These notes accompanied by a sketch of a rotatable disc indicating positions of holes

 

f.5: sketch of a rotatable disc with a radial row of three holes.

'leaving room for possible cuts a row with movable windows.'

'On one side have the sliding flap which blocks a row entirely.

On the other side have the arrangement providing variety of cut & shape.'

 

f.6: set of rough working sketches.

 

f.7: sketch of the pendulum with notes:

'Sheath[?] of pendulum provided with [adaptable?] slit.'

'4 in 1 radii - 1/4 inch holes in plate

3 concentric circles leaving room for 1 each corner. Circle at periphery allows for movable slots. [small sketch of circular device with lever here] shutters on side of plate. Arrangement for diaphragm [sketch of diamond, rectangle, circle and squate 'etc'] on other side of plate.'

 

f.8: circular piece of card marked on one side with radial lines and concentric circles, with eight holes cut into it around inner circle. On the reverse, squares are drawn around two of the holes.