build castles in that region for half-an-hour or so, then pack up shirt A, and do the last stage of your day's walk at a swinging pace in the cool evening. Shirt A does duty as a night-shirt, B is resumed on the next morning, when A " goes to the wash," as B did the day before.

The success or failure of a pedestrian excursion of any length depends primarily on the reduction of luggage. Everybody takes too much. I did so on this occasion, having included a comb and hair-brush, besides the above-named collars. On reaching Christiania I had my

remember ever to have seen a flannel one in use, either above ground or in a coal-pit. The comfort of the huckaback shirt is unquestionable.

TH

THE

ILLUSIONS OF THE SENSES.

BY RICHARD A. PROCTOR.

(Continued from page 40.)

of heat is in like manner usually associated

sently I discovered that there remained on my head nothing to brush, and less to comb. The Norwegians clip their horses annually, themselves likewise, and in the same degree. The only occasion on which I did not take an excess of luggage was on a suddenly extemporised trip through Belgium, the Rhine, Bavaria, the Tyrol, Venice, the Italian lakes, Alsace vid the Splügen and Zurich, thence by the Moselle to Nancy, and from Nancy to Paris by rail. My luggage on starting from London by the Dunkirk packet was a penny sheet of brown paper and a bit of string. Every other requirement was purchased on the way as the demand arose. The natural course of evolution in this case finally converted the sheet of paper into a German satchel filled with handbooks and photographs. If you eat a raw turnip or a hard apple every morning, the supposed necessity for a tooth-brush is refuted by a reductio ad absurdum.

So far I have only considered clothing material in relation to its resistance to the passage of heat and the transpiration of aqueous vapour. The saline constituents of the perspiration are very variable in composition; varying with different individuals, and in the same individual at different times, according to the conditions of health, exercise, climate, and food. To these variations I attribute the contradictory results obtained by able chemists and physiologists who have collected and analysed these secretions. I will not enter upon the details of such analyses, especially as I have recently discussed them in connection with the physiology of nutrition in my papers on "The Chemistry of Cookery."

At present it is sufficient to note that there are given out either urea itself or nitrogenous salts of similar composition and physiological significance; salts which are products of the degradation of tissue, and therefore constituting excrementitious matter, which is more or less poisonous, and should be removed. The foulness of the arm-pit portion of a dirty shirt, or the feet of over-worn socks, indicate this, and prove the necessity of frequent changing of underclothing.

In reference to these, I am inclined to conclude that my towel shirts, described in the last paper (I learn that the technical name of the material is "huckaback "), are better than flannel. Flannel assists gaseous transpiration better than the towelling; but this is decidedly superior to flannel in removing the liquid perspiration, and all that it holds in solution. This may be tested by simply washing one's face, and then wiping it with flannel, as against good soft huckaback. Therefore, I conclude that persons who are troubled with excessive liquid or sensible perspiration may find the towel shirts even better than flannel. Should any of my readers repeat my experiment, they will do good service by recording the results.

The experience of furnace-men is in favour of such material. I have seen much of them, and find that the "mop," which is thrown loosely round the neck or over the shoulders, and used for wiping or mopping the face and breast, is usually of towelling material. I do not

with

are either corrected or modified by visual impressions. Yet there are cases where this sense is deceived when acting alone. For instance there is the well known experiment in which after one hand has been placed for a time in water as hot as can be borne, and the other in ice-cold water, both hands are plunged simultaneously into tepid water. Immediately the hand which had been in very hot water recognises a comfortable sense of coolness, and as it were pronounces the water cold; the other hand as quickly recognises a comfortable sense of warmth and pronounces the selfsame water hot. Here even sight will not correct the illusion. We see as plainly as possible that both hands are in the same basin, yet one hand seems to be in warm water the other in cold. I find a singular effect produced if while the attention is strongly directed to the circumstance that both hands are in the same water, the hands are freely moved about in the water. For it seems then as though there were currents of hot and cold water in the same basin, moving so as to follow or rather to accompany the hands.

Without making definite experiment in this way, we can easily in the ordinary experiences of life, recognise the readiness of the heat sense to be deceived. Thus we come out of a warm room into the hall outside and find the air there pleasantly cool. We then, perhaps, see a friend home through the cold night air and presently return to the same hall. But now, coming into it from the cold outer air, we find it pleasantly warm.

Professor Le Conte remarks that "during the Arctic voyages made by Parry, Franklin, Ross, Kane, Nares, and others, it was found that a zero temperature seemed quite mild after the thermometer had been twenty or thirty degrees below that point." But, although in California temperatures of twenty or thirty degrees below zero may not be common, an American has no occasion to leave the United States, or even the middle states, to experience the illusion in question. I have repeatedly walked along the streets of New York with the temperature a degree or two below zero, without wearing an overcoat or feeling the want of one, when such a temperature has followed a few days of much colder weather. And conversely, even as I write I am feeling unpleasantly cold at Columbia, South Carolina, with the temperature only just below zero (and the air still), simply because I have been enjoying during the last few days in Charleston, S.C., a soft and balmy warmth resembling that of a June day in England.

Again in caverns like the Mammoth Cave, Kentucky, or Kent's Hole in Devonshire, there is in summer always a sense of coldness and in winter always a sense of heat, yet in reality the thermometer shows that, as might be expected, the air is somewhat warmer within such caves in summer than it is in winter. Here, then, the illusion is not only incorrect but the very contrary of the truth, the air seems colder when it is really warmer and warmer when it is really colder. Because the range of tempera

A more subtle illusion relating to heat is that arising from difference in the conducting power of various substances with which the skin is brought into contact. Thus if we plunge into water of the very same temperature, when tested by the thermometer, as the surrounding air, both being really cooler than the body, the water seems cold, because being a better conductor than air, it immediately begins to carry off more of the body's warmth. On the contrary, the self-same substancewater not only feels hot but is unbearably hot when at a temperature far below that of the surrounding air in a Turkish bath.

It is to be noticed that in this case the sense of heat while in one respect leading to an erroneous idea, in another and a much more important point gives correct information. If one were to trust the teachings of the thermometer, and infer that one might as well remain in water as in air seeing that the water and the air are of the same temperature, one would make a serious mistake, and suffer a good deal of harm through the rapid abstraction of warmth from the body. The heat sense, by telling us wrongly that the water is colder than the air, conveys at least the much more important information that we are losing heat while in the water, and therefore saves us from the danger of getting unduly chilled, as we might if we trusted to the thermometer alone. In the reverse case, the sense of heat acts even more directly and emphatically for our benefit. I remember a case in point which occurred at the Hummums. Some one who had heard that the temperature of water in the hot rooms is always much lower than the temperature of the air, but had not considered the matter with actual reference to the requirements of the human body, supposed that he would gain decidedly in comfort if instead of sitting on the non-conducting felt or flannel of the seats, he were to substitute a roll of towels well soaked in water. He found as a matter of fact that the arrangement thus suggested by the thermometer was very far from being welcomed by the nerves of touch, whose repugnance to the arrangement was indeed most emphatic.

It is hardly necessary to say, perhaps, that the whole question of clothing, especially for young people, depends on the relation between the conducting powers of various substances used for clothing. In this matter the sense of heat gives more trustworthy information than the thermometer, clothes which seem to be of the same temperature if tested by the thermometer affording very different degrees of protection against the loss or the too rapid

accession of heat.

In passing, I may note here an important consideration as to the clothing proper for children. In their case as in the case of grown folk the sense of heat gives the best information as to what is really desirable in the way of clothing. But grown people are apt to forget the experiences of their childhood, and to decide what is best for children from their own ideas as to what ought to be best. A child complains of cold or of heat sooner than a grown person; but much less attention is paid to the complaints of children on such matters than to our own slightest suggestions of personal discomfort. And children are much less carefully guarded against heat and cold than grown persons guard themselves. The idea seems to be that children can stand any changes of temperature; though, oddly enough,

children's own idea (which is really not very far from the truth) that they can stand anything in the way of rich and indigestible eating, is not much considered by older persons. Now when a child shows by its words or actions that it suffers sooner from changes of temperature than grown people do, it in reality expresses its sense of an important truth. A child cools and warms more quickly than a man; for precisely the same reason that a small cinder cools more quickly than a large one, or that a small fire burns out more quickly than a large furnace. Compare the case of a child three feet high with that of a man six feet high. Neglecting slight differences of build, the man is about eight times as large as the child, or contains eight times as much matter. But the surface of the man is not eight times as large as the surface of the child; it is only four times as large. Thus supposing the man and the child to come out of a warm room into the cold outer air, being both at the same temperature, the man has eight times as much heat to part with as the child has; but he only parts with four times as much heat, moment by moment, if he and the child are similarly clothed. Thus the child's loss of heat, moment by moment, though only one-fourth of the man's loss of heat, bears twice as great a ratio to the child's total supply of heat. The child will cool as much in one minute as the man cools in two minutes, or in half-an-hour as the man cools in an hour. If the weather outside is so cold that the man would suffer serious injury to his health after an hour's exposure to it, the child will suffer at least an equal injury in half-an-hour. In reality of course the child will suffer a greater injury; because apart from his more rapid loss of heat, the child's flesh is more tender and necessarily suffers more from a given loss of temperature. Similar remarks apply to increase of heat, which may be just as mischievous as access of cold. Yet we are too apt to clothe children with total disregard to the circumstance that they require to be protected much more carefully than their elders against rapid changes of temperature. Apart from all questions of propriety a man would not care even on a fairly warm spring day to go about with his arms. and legs bare for any length of time; for he would feel uncomfortably cool: children suffer twice as much on such a day from undue exposure to the air; yet many foolish folk think nothing of exposing the delicate limbs of children to the cold of winter without protection. They imagine that the numbness and insensibility which really indicate the mischievous effects of the cold, and may permanently affect the child's constitution, are signs of hardening; and because only the hardier survive this cruel treatment they imagine that those hardy survivors owe the strength which enabled them to survive, to the harsh exposures by which that strength was dangerously taxed and perhaps in large measure sapped.

(To be continued.)

THE "Visitation of Dorsetshire," and the "Visitation of Gloucestershire" of 1623, have just been issued by Messrs. Mitchell and Hughes to the Members of the Harleian Society. The two volumes are included in the subscription for 1885; and the second volume of the Registers of St. James, Clerkenwell, will be ready for the Members in August.

BURNHAM BEECHES.-In a special "Holiday Edition" of Mr. Francis George Heath's "Burnham Beeches," to be published immediately by Messrs. Rider & Son, of Bartholomew-close, will be included a portrait of the author, upon whose suggestion this charming tract of forest was secured for public use by the Corporation of London.

7

A FAST STEAM-YACHT.

Femboat Mary Powell has been recognised as the

NOR more than twenty-two years the side-wheel

fastest boat on the Hudson River; she makes an average of twenty miles an hour, and according to a pamphlet issued by the owners, "in the year 1882, she ran at the very fast rate of 26 miles an hour between Milton and Poughkeepsie, making the four miles in nine minutes." Boats of all sorts of shapes, big and little, side-wheels and propellers, have unsuccessfully attempted to wrest from her the well-earned title of Queen of the Hudson. But on June 10 she was badly beaten in a long run by a small steam-yacht of very insignificant appearance. The run was from this city to Sing Sing, a distance of 30 miles, and was made by the steam-yacht Stiletto in one hour and fifteen minutes, the Mary Powell, on her regular trip to Rondout, being beaten about two miles.

The Stiletto was designed and built by the Herreshoff Manufacturing Co., of Bristol, Rhode Island. She is 94 ft. long over all, 90 ft. on the water-line, and 11 ft. beam. The hull is double planked, and sharp at both ends, the curves extending far toward the centre. A slightly arched deck covers the whole boat. Forward is a pilot-house sufficiently large to serve as a commodious cabin. Owing to the extremely small space taken up by the engine and boiler rooms, there is ample room for comfortable quarters for the crew and state-rooms for the owner, guests, and officers. Power is furnished by a compound condensing-engine of 12-inch stroke and cylinders 12 and 21 in. in diameter; the engine is supplied by a sectional water-tube boiler, in which steam can be got up quickly, and which is calculated at 450 horse-power. Although this boiler is similar in principle and operation to those of the regular Herreshoff type, it varies greatly in construction, the tubes being arranged horizontally in sets immediately over the fire-each set being at right angles to those just above it. Exhaust steam is led to a surface condenser. An ordinary pump takes the water from the condenser, forces it into the upper set of boiler tubes, through the boiler to a sepa

rator located in front of the boiler, and to which the steam-pipe is connected. The boiler will work safely with 160 lb. of steam, but in the race with the Mary Powell it was only found necessary to use from 120 to 125 lb. The fire-box is 61 ft. square.

The screw is four-bladed, 4 ft. in diameter, and 6 ft. pitch. At the stern the boat draws 4 ft., and at the bows 3 ft. We may notice that there are now building at the yards of Yarrow & Co., England, two torpedo boats which are expected to run, when light, at the rate of 24 knots an hour, or nearly 28 miles. The Stiletto must do better than 25 miles an hour before she can claim the broad title of the fastest boat in the world. Scientific American.

IF

F we consider what really happens when (as supposed to be seen from the moon) the sun is passing behind the earth, and therefore the earth's shadow is thrown on the moon, we shall readily understand the increase of the earth's effective shadow-throwing diameter by about onesixtieth part,-a circumstance which some so strangely misinterpret, that they appear to imagine a range of play a part in determining the phenomena of a total lunar 60 or 70 miles of our atmosphere above the sea-level to eclipse!

outline of the earth ECE' passes through C the centre Suppose ESE', Fig. 1, the face of the sun when the of the sun's disc, k Kk', Ll', m Mm', and e Se' being the advancing edge of the earth at equidistant times up to the summit of geometrical totality. Then obviously, as

The mistake is very commonly made of attributing this increase to the earth's atmosphere. In reality the earth's atmosphere has nothing to do with it.

portion is also rapidly diminishing. If we drew, as in Fig. 2, a diagram, such that, OX and OY being axes, O C, OK, O L, and OM represented the breadths SC, SK, SL, and SM of Fig. 1, then if the illumination received when the earth's edge is at C, Fig. 1, were represented by the ordinate Cc, Fig. 2, the illumination when the earth's edge reached K, L, M, Fig. 1 would be represented by such ordinates as Kk, Ll, Mm. Here OM would correspond to about 4'. Suppose, now, another diagram made, as in Fig. 3, in which O M represents the OM of Fig. 2, enlarged, and Mm represents the ordinate M m of Fig. 2, enlarged in much greater degree. Then the earth's further progress as SM of Fig. 1 is traversed, minute (of arc) after minute, carries the edge to the points P, Q, R, Fig. 3. The illuminationordinates shorten now much more quickly than those in Fig. 2. We get such a curve as mpqr, where Q q is less than a fourth of M m, but Rr less than a tenth of Qq (the real proportions are probably somewhere about this). We see then that if s Ss, Fig. 4, represent a part of the edge of the geometrical shadow of the earth on

Fig. 3.

Fig. 4.

Fig. 2. the moon, r Rr and qQq' rings respectively l' and 2' from that shadow, the average illumination over the area q Rq' is greater than that over the area r Sr', somewhat as the area RrqQ in Fig. 3 is greater than the area O Rr. Now if Orqpm in Fig. 3 were a parabola, the area RrqQ would be seven times OR r. But we have seen that in passing from M to O we get ordinates shortening far more rapidly the nearer we draw to O. Hence the illumination of q R q' exceeds the illumination of rSr' in far greater degree than this,

probably (as I find from a construction based on a fair estimate of the degradation of the sun's lustre near the edge) at least a hundred times. We cannot wonder, then, that to ordinary eye-sight (that is, regarding the eye as measuring the light without photometric aid, though aided of course by the telescope) the transition from light to darkness is so rapid that all within the circle r Rr' appears dark and all within q R q' appears light. The glare from the rest of the moon's surface helps still further to deceive the eye; as we learn from the sudden change of aspect when that glare is gone,-the part within s Ss' which had seemed nearly black, appearing thereafter (if refraction sends any light to it, as ordinarily happens) to glow with a considerable amount of ruddy lustre.

Mr. Ranyard's remarks about refraction diminishing the area of the shadow seem based on the mistake to which I have already adverted, by which he has apparently overlooked the exceeding narrowness of the atmospheric zone which can refract the sun's light into the shadowed region. If we could consider, as he seems to do, the amount of refraction to indicate the degree to which the shadow might be diminished, then indeed the perplexities into which he seems to have involved himself might be understood. But as a matter of fact (or of calculation, if that be preferred) refraction even though effective to the very sea-level all round the earth's disc as seen from the moon, cannot affect the shadow's size in the slightest degree. The size of the shadow depends on the position of the ring (see Fig. 4) at which the degradation of light is so rapid that the eye recognises a marked and sudden darkening; and this, as we have seen, must occur somewhere outside the geometrical shadow. (The question is rather physiological, though, than physical.) Refraction can temper the darkness of the umbra, but cannot in any way affect its size. All over the umbra refraction is at work, usually with tolerable uniformity, carrying a certain small proportion of sunlight, variously coloured according to atmospheric conditions, to illuminate the moon's surface. If one part of this surface is illuminated by a longer arc, or by an entire ring, than another, this other is illuminated by a broader and brighter one. All parts get nearly the same amount of light-at least, the absolute difference is everywhere very small compared with even the difference between the illumination along rRr', Fig. 4, and that along & Ss'.

So soon as no direct light from the sun falls on the moon, and only refraction even the most effective refraction- -can carry light to her surface, we have necessarily a very feeble light indeed,-even though, as I showed (or rather explained) in my former papers, the light then received is true sunlight, not merely light from our illuminated air, as Mr. Williams supposed.

Compare, for instance, the light received from a crescent of the sun l' wide as seen from the moon, with the light from the complete ring round the earth into which the sun is distorted when centrally behind the earth, the zone of atmosphere bordering the earth's disc being supposed two-thirds clear of clouds down to the sea-level and of its average transparency. I take the average brightness of the crescent of sunlight to be about one-fifth the average brightness of the solar disc, and the area of the crescent about 1-700th part of this disc. I also assume the average absorption of sunlight in passing through our atmosphere grazingly between altitudes O and two and a half miles to be 19-20ths, the ordinary coppery light of the totally eclipsed being such as to suggest at least this amount of absorption, and the real

absorption being probably considerably greater. We have then to compare two illuminations, one from an apparent surface equal to 1-700th of the sun's and of an average intrinsic lustre equal to onefifth of his; the other from an apparent surface corresponding to two-thirds of a ring around the earth's disc, about two and a half miles in width and of only 1-20th the sun's intrinsic lustre. Now the apparent size of this ring round the earth, as seen from the moon, has been shown (see KNOWLEDGE for April 24, 1885, p. 341) to be 1-889th of the sun's apparent disc. Hence the ratio we require is

or

1 1 1 1 2
X X
700 5 889 20 3
5334 700, i.e., nearly 8 to 1.

Yet we have seen that along r Rr', Fig. 4, or l' from the edge of the geometrical shadow, the eye recognises so great a loss of light that the shadow seems to occupy the space r Sr'; how little then can any part of the shadow within s S s' be affected by the small modicum of refracted light which can fall there, even under conditions rather more favourable than usually exist.

I have not thought it necessary so far to take special account of the action of the higher layers of the air, in bringing light within the geometrical shadow. action has to be considered in two aspects. In the first

Fig. 5.

This

place it increases, so far as it is effective at all compared with direct light from the sun, the amount of light falling outside s Ss' Fig. 4. For so soon as the sun even begins to pass behind the earth, as seen from the moon, refraction is at work in bringing the geometrically hidden parts of his disc into view. But such parts must necessarily be intensely flattened-so to speak, and the amount of light reaching the moon through such refractive action must always be very small compared with that which arrives directly, so long as any part of the sun's face remains unconcealed (geometrically) by the

earth.

Suppose, for instance, three-fourths of the sun's diameter covered, geometrically. Then the sun as seen from the moon would be wholly visible, in the shape shown in Fig. 5, the part really behind the earth being compressed into a thin zone along e E e', the inner edge of this zone being raised a mile or so above the earth's true outline. (It would only reach this when the sun had passed so far into the shadow that only actual grazing refraction would bring him into view.) Beyond e and e' would be two fine arcs of light extending to k and k', where lines from C the centre of the earth's shadow touch the disc of the sun. The centre of the sun being about 8' below (or rather within) E would be raised into view by the action of that layer of air which for an observer on earth would produce a horizontal refractive of 4', about one eighth of the horizontal refraction at the sea-level. This would

correspond to an elevation of about 11 miles. The atmosphere 14 miles above the sea-level would bring up only about 4' of sun breadth; the atmosphere 17 miles high only about 2'. Now it takes a depth of nearly 70 miles of our atmosphere to subtend l' at the moon's distance. So that the zone bringing any appreciable amount of refracted light, would be very narrow indeed.

Probably I am far within the truth in saying that if the sun had just set geometrically behind the earth, while the part of his disc farthest in would appear about three-quarters of a mile above the sea-level, the part just within (geometrically) would not be apparently raised more than twenty miles above the sea-level by the refractive action of that portion of the air effective in bringing it into view. The illumination derived from the meniscus arc of light so showing would be very small compared with full sunlight-possibly about 1-10,000th part on the average. In colour it would be but slightly tinged with red, under ordinary conditions, so slightly that probably by comparison with parts of the moon further within the earth's geometrical shadow, illuminated by ruddier light, this portion would look slightly bluish. It would be a very narrow zone of shadow, however.

WE

THOUGHT AND LANGUAGE. BY ADA S. BALLIN.

XIII.

E have seen that the deaf-mute thinks and reasons and finds a means for expressing his thoughts; but we have not yet touched upon the question of how he thinks. The question of the manner in which thought proceeds is one of great interest, but it is one to which very little attention is paid except by psychologists. If an intelligent and well-educated person, with all his senses intact, is asked the usual form of his thoughts, he will generally be at a loss what to answer, and this arises from the fact that, as a rule, we think, but are not conscious of the act of thinking, and pay no attention to it. If, however, we do turn our attention inwards we find that for the most part we think in imaginary sounds. As Goethe says, man is a creature of custom :

Aus der Gemeine ist der Mensch

Und die Gewohnheit nennt er seine Amme. We are so accustomed to express our thoughts in certain varied groups of sounds which we call words, that we chiefly think, as it were, in suppressed sounds or words. It is this fact that led to the confusion of thought with speech among the ancients, who held that thought and speech are identical, except that thought "is the unuttered conversation of the soul with itself, and that the stream of thought which flows through the lips and is audible is called speech," according to Plato's summary of the matter in the "Sophist."

If we look closely into the question we find that thought and language are by no means identical, although so closely associated by habit. For example, the same thought may be expressed in half-a-dozen different ways, and we select that which seems most suitable to us, while at other times a thought presents itself to the mind and we find the greatest possible difficulty in clothing it with words. Further, while all nations have to a great extent the same thoughts, each has a different way of expressing them. I have previously compared words to coins which take the place of articles alike cumbrous for transportation or storage; and, in fact, they are handy