trolley-cars cannot, however, be recommended as a strengthening tonic.

The colours also affect the squeeze with some persons, especially hysterical people. The strongest hand-squeeze in the case of one such subject is shown in Fig. 61. This suggests a new principle in the selection of colours for the house, for uniforms, etc.

Tastes and smells have different

FIG. 62.-Influence of Musk.

effects. Fig. 62 shows the effect of musk, which was smelled just as the Tobacco has

FIG. 61. Strongest last squeeze was made.

Contractions while
Looking at differ-

green; b, blue ;

ent Colours: 9, a stimulating effect. Joy and anger 6, orange; y, yel increase the power, sorrow and fright low; r, red; v, vio- decrease it. An entertaining novel is a will-stimulant; a prosy text-book actually weakens us.

let.

H

CHAPTER VIII

TOUCH

ERE is a row of ten little disks, 3mm in diameter, cut from elder pith. Each is suspended by a fine cocoon-fibre from a little handle. For portability the handles are stuck in holes in a support (Fig. 63). Now place your hand comfortably on the table and close your eyes. Tell me when and where you feel anything touch your hand. Without letting you know what I am doing I take the handle with

the lightest weight and let the weight softly down till it

rests on your hand (Fig. 64). You do not know

that I have done

I

so, and you feel FIG.63.-Touch-weights for Finding the Threshold. nothing. Then I try the next heavier, and so on, till you feel the pressure. The little disks are graded in weight, thus 1mg, 2mg, etc., up to 10mg.

Now, if the fourth weight was the first you felt, then 4mg was the least noticeable weight, or the weight just

on the "threshold of intensity." This fact of the threshold is one that we shall meet everywhere in the study of mind.

The threshold of sensation for the sense

of

pressure in an average subject was 2mg for forehead, temples, and back of forearm and hand; 3mg for inner side of forearm; 5mg for nose, hip, chin,

FIG. 64.-Finding the Threshold for the
Palm of the Hand.

and abdomen; 5mg to 15mg on inner surface of fingers; and 1000mg on heel and nails.

Some idea of the delicacy for distinguishing differences in pressure can be obtained by laying a hair on a plate of glass and putting

over it ten to fifteen sheets of writing paper. The position of the hair can easily be felt by passing the finger back and forth over the surface.

Touching with movement gives much more delicate judgments than mere contact. A book-cover feels much rougher when the finger is moved over it than when it is merely touched.

Something very peculiar occurs when a light pressure is varied rapidly in intensity. If the tip of tuning-fork in motion be lightly touched to the skin, it "tickles."

The tickling need not be a true wavy pressure; that is, it need not be perfectly regular. If any object, such as a feather or the finger, be held lightly

against the face, a tickle is felt, due to the trembling. The tickling thing need not stay at one spot, but may be moved along continuously. A feather drawn over the temples makes a strong tickle. A fly walking over the skin produces an unbearable tickle in exactly the same way. Stories of the Thirty Years' War relate how the soldier-robbers forced the peasant to reveal his treasure by subjecting him to unbearable tickling. Salt was spread on his soles and a cow was allowed to lick the salt.

When a pressure is already felt, it can be made stronger or weaker to a certain degree before the change is perceived.

FIG. 65.-Finding the Least Noticeable Change in Pressure.

The experiment can be made with a pair of beambalances. The hand, supported by a block or cushion,

is placed under the scale-pan so that when the scale is at rest, the pan-holder just touches the skin (Fig. 65). To avoid the coldness of the pan, a piece of cork or leather is placed between the hand and the metal.

The subject of experiment closes his eyes. A weight is placed in the pan above the hand. A sensation of pressure is felt. Sand is quietly poured into the same pan until the subject feels the pressure to be increasing. By putting weights in the other pan the amount of increase can be measured. Now start with the same weight as before and pour sand into the opposite pan until the subject feels the pressure to be lighter. The amount of sand that has been added represents the least noticeable change, or the threshold of change, in the pressure. Thus, if the weight at the start was 50% and the amount of sand added was 358, the least noticeable change was 35%, or of the original

pressure.

Several facts will be noticed by those who perform this experiment. In the first place, the least noticeable change depends on the rate at which the change is made. Several funnels should be used, with the ends of different sizes. When one of these is filled with sand, the rate at which the sand flows out depends on the size of the opening; some funnels will allow the sand to flow rapidly, others slowly. When the same experiment is repeated with different rates of flow, it will be found that the slower the flow the greater the least noticeable change. With a very slow flow the weight can often be increased two or three times over before the change is noticed.

No one has ever tried to see if a great pressure can