uscular exercise
throughout.

In performing colour experiments, several requirements would appear to
be necessary for exact results. Should not the colours chosen be equal
in purity, intensity, lustre, illumination, etc.? In reference to
these differences, I think only that degree of care need be exercised
which good comparative judgment provides. Colours of about equal
objective intensity, of no gloss, of relatively evident spectral
purity, under constant illumination--this is all that is required. The
variations due to the grosser factors I have mentioned--such as
condition of attention, physical unrest, disturbing noises, sights,
etc.--are of greater influence than any of these more recondite
variations in the stimulus. Intensity and lustre, however, are
certainly important. It is possible, by carefully choosing a room of
pretty constant daylight illumination, and setting the experiments at
the same hour each day, to secure a regular degree of brightness if
the colours themselves are equally bright; and lustre may be ruled out
by using coloured wools or blotting-papers. The papers used in the
experiments given above were coloured blotting-papers. The omission of
yellow is due to the absence, in the neighbourhood, of a satisfactory
yellow paper.

The method now described may be further illustrated by the following
experiments on the use of the hands by the young child.

_The Origin of Right-handedness._--The question, "Why are we right or
left-handed?" has exercised the speculative ingenuity of many men. It
has come to the front anew in recent years, in view of the advances made
in the general physiology of the nervous system; and certainly we are
now in a better position to set the problem intelligently and to hope
for its solution. Hitherto the actual conditions of the rise of
"dextrality" in young children--as the general fact of uneven-handedness
may be called--have not been closely observed. It was to gain light,
therefore, upon the facts themselves that the experiments described in
the following pages were carried out.

My child H. was placed in a comfortable sitting posture, the arms left
bare and free in their movement, and allowed to reach for objects placed
before her in positions exactly determined and recorded by the simple
arrangement of sliding rods already described. The experiments took
place at the same hour daily, for a period extending from her fourth to
her tenth month. These experiments were