(1) Mark out, by indelible ink, a sq. cm. upon the outer surface of the forearm. Make upon transparent paper three maps of the area, marking hairs, veins, etc. Work over the area (a) with the horsehair, for pressure spots; (b) with a warmed carpenter’s spike, for warm spots; and (c) with a cooled spike, for cold spots. Enter the spots, as you find them, on the maps; remember to dot the hair down for pressure, but to draw the spike slowly and evenly along the skin for temperature. Lay the three maps together, and note the distribution and the relative number of the spots.
(2) After shampooing, the scalp is sensitive and irritable under the brush. Why?
(3) When you are writing with a pencil, or prodding in a pool with a stick, the sensations seem to come from the end of the pencil or stick. What organs are involved? And why should the sensations be localised as they are? Try to think out some experimental means of attacking this question.
(4) What sensations do you get in the act of yawning? What in that of swallowing? What unusual sensations do you have, from the face, after you have been running hard?
(5) How do sour and sweet in the mouth affect the sense of touch? Make solutions, in varying strengths, of sugar and of the juice of some very sour fruit; leave plenty of time between observations.
(6) Prepare some bits of apple, onion, and raw potato. Close your eyes and hold your nose; then pick up these morsels at random, and chew them. Can you tell the difference? How?
(7) Is there any evidence of taste contrast?
(8) Secure adaptation to the scent of camphor; breathe regularly, and note the length of time necessary for the odour to disappear. Now smell at vanilla, heliotrope, absolute alcohol. Do you smell them? Try to account for the result, arguing by analogy from what you know of colours.
(9) The next time that you listen to an orchestra, pick out the tones of the various instruments, and try to describe their timbre; do not be afraid to string adjectives together, but be sure that you hear what you put down. Later, look up in a reference-book the composition of these various compound tones, and see if there is any correlation between your description and the number and loudness of the overtones.
(10) If you drop a block of wood on a desk, the sound is simply noisy. If the same block forms part of a xylophone scale, and is struck with the wooden hammer, it gives a tone. How is this?