of the origin of language, each accounting for it by one cause and ignoring all other influences. We have had the Onomatopoetic, or imitative theory; the Interjectional, which maintains that language is derived from the imitation of interjections; and, finally, Max Müller's theory that, as everything in Nature produces certain sounds or rings, language has its origin in this. The first two theories have been nicknamed by Max Müller the Bow-wow and Pooh-pooh theories; while, in revenge, Prof. Whitney has called the last the Dingdong theory. These nicknames perhaps show better than anything else the utter contempt in which each party holds the hypotheses of the others, yet each has a certain amount of right on his side, and all might be reconciled to each other, and from the materials of their own form a theory which would be in accordance with all the facts in our possession if they would only be convinced that, into a great and complicated matter like that under discussion, a variety of elements must necessarily enter. This truth was evidently partially grasped by Plato, and it has been clearly brought out by Jowett, both in the preceding passage and in the succeeding, which I quote as a model of liberal thought and clear exposition of a difficult point. He continues:

"Neither is Plato wrong in supposing that an element of design and art enters into language. The creative power abating is supplemented by a mechanical process. Languages are not made, but grow' but they are made as well as grow; bursting into life like a plant or flower, they are also capable of being trained, and improved, and engrafted upon one another. The change in them is effected in earlier ages by musical and euphonic improvements; in later ages by the influence of grammar and logic, and by the poetical and literary use of words. They develop rapidly in childhood, and when they are full grown and set, they may still put forth intellectual powers, like the mind in the body; or, rather, we may say, that the nobler use of language only begins when the framework is complete. The savage or primitive man in whom the instinct is the strongest is also the greatest improver of the forms of language. He is the poet or maker of words, as in later ages the dialectician is the definer or distinguisher of them. The latter calls the second world of abstract terms into existence, as the former has created the picture sounds which represent natural objects or processes. Poetry and philosophy-these two are the two great formative principles of language when they have passed their first stage, of which, as of the first invention of the arts in general, we only entertain conjecture. And mythology is a link between them connecting the visible and the invisible, until at length the sensuous exterior falls away, and the severance of the inner and outer world of the idea and the object of sense becomes complete. At a later period logic and grammar, sister arts, preserve and enlarge the decaying instinct of language by rule and method, which they gather from analysis and observation." *

For

supplementing that explanation was found by some to have the effect of making clear to them how imperfect had been their previous knowledge of the matter, and how incorrect had been many of their notions respecting it. I had already recognised that this must be so. those mistakes and misapprehensions which I had proposed to correct (those, that is to say, which I had noticed in Mr. Mattieu Williams's "Science Notes" in the Gentleman's Magazine) showed clearly that the general reader must be apt to misunderstand the usual explanation altogether. I had also noticed mistakes by others who might have been expected not only to follow understandingly the correct (but incomplete) explanation given by Sir John Herschel, but to be capable of interpreting the matter for themselves.

I propose now to consider, not those circumstances which I dealt with before, but the preliminary explanation, which I assumed before to have been to some degree mastered and understood. I deem it a duty to do this, and to do it in these closing numbers of the weekly KNOWLEDGE, because many seem to imagine that the matter is in some degree in dispute; whereas the only difficulty there really is in the matter is to make that clear which everyone acquainted with the laws of geometrical and physical optics knows to be true.

Mr. Williams, indeed, considers that he has been entirely misunderstood by me, a supposition natural enough in such cases, where there will generally be misapprehension even on the part of those who have mastered a subject-misapprehension as to the exact way in which the facts have been misunderstood. One is apt to suppose that this particular mistake is likely, and that mistake impossible, when, as it turns out, it has been the seemingly impossible mistake, not the likely one, which has really been made. For this reason I will not follow the rather confused reasonings by which the mistaken views I set out to correct have been supported. I will not endeavour to ascertain from them precisely how those mistaken views arose. In the advocacy of mistaken views there is necessarily confusion often. worse confounded than the original mistake).

I take then the mistaken notion that during total lunar eclipse the moon is lit up only or chiefly by light from our illuminated atmosphere, the ruddy twilight glow in our air,-not by rays which have come from the sun himself, in the same way precisely that rays come to us from the setting sun. That this mistake was originally made by Mr. Williams is obvious in two ways: First it was essential to the theory in hand that this misapprehension should be entertained, and secondly the mistake was directly involved in the deduced estimate of the amount of sunlight falling on the moon during totality. Remove this mistake, and the theory of a self-luminous moon is at once shown to be superfluous,-and (through its superfluity) as impossible as water standing an inch above a goblet's brim.

The mistake evidently had its origin in the idea that when the earth lies between the sun and moon, the atmosphere of the earth plays the part of the outer shell of a spherical lens, bringing the solar rays to foci between the earth and the moon. The idea manifestly was-and and I find the idea is quite commonly entertained that the moon, being set where she is, at the time of central eclipse, receives rays corresponding only to that particular position of these imagined foci which brings them at or near her surface. The fact that rays from every part of the sun reach the moon if she is beyond her mean distance, and from nearly every part when she is in perigee (rays

from every part of the sun reach nearly the whole of the moon's surface even then), that in point of fact the sun would be absolutely visible, though distorted, from every part of the moon's surface at the time of central total lunar eclipse, is regarded as incredible. Yet it is the simple truth.

This is precisely the fact which I not only took for granted, but which I treated-in my former papers-as a fact which should be obvious to every one likely to be studying this subject at all. The only difficulty I could see-in fact the only difficulty there is, but it is much more troublesome than I imagined is a difficulty which would quite as much trouble an unsound reasoner in trying to determine whether the sun would be visible through the effects of refraction after he had really set in the geometrical sense. If we did not actually see the sun in this way, I imagine we should find many persons capable of clearly proving that the sun could not be so seen, or only by a very small portion of his light. One of these misapprehending perhaps an explanation by Sir John Herschel-might reason thus:

Suppose HE to be the plane of the horizon, and put HA to represent the air at H (it is a little wild to represent the air by a straight line, but Herschel, who unfortunately seems to have had little skill in planning diagrams, represents the earth herself by a straight line in the corresponding part of his explanation of the ruddy eclipsed moon) E, the eye of an observer. Then if a ray SA from the sun S below the horizon is refracted in the direction A E, it will reach the observer at E, but only just that ray; for a ray Sa will be refracted to e far on one side of him, and a ray Sa' will be refracted to e' far on the other side of him. Therefore he will get but the merest fraction of the sun's light, and to say that he will

actually see the sun, (apart from atmospheric absorption)

as well as if the sun were above the horizon is absurd on the face of it. And so forth.

Only, as a matter of fact we see the sun, and so this false reasoning never gets fairly started,-as the corresponding false reasoning about the ruddy eclipsed moon very naturally has been.

Now let us consider the real facts in regard to the

moon.

a

Fig. 2.

Let the lines in Fig. 2 be supposed to represent rays coming from a point on the sun, very far away on the left to the earth E and the moon M at the time of total eclipse. The rays which come through the atmosphere at a and a', just touching the earth are bent through an angle of about 34' as they enter and as much as they pass out, so that they are deflected through an angle of about

68' in all and cross at a point as c which lies on the line E M, not far from the moon M, because the angle a M E (or more precisely because the angle whose sine is Ea÷ EM) is only about 58', whereas the angle a c E is about 68'. Rays which pass higher up, as at b and b' are deflected less, and cross as at c', on EM produced, farther and farther away till we get no deflection at all and the rays simply radiate on straight lines diverging from the particular point on the sun we are considering. If b, b', are at a height of 3 miles where the atmospheric density is reduced one half, the deflection will be about one half what it is at the sea-level, or the angle bc' E about 34°, so that rays travelling so high in our air would pass considerably beyond the moon when she is situated as shown in Fig. 2, supposed to correspond to the time when the particular point on the sun considered is just centrally beyond the earth supposed to be seen from the moon.

So far we have what Sir John Herschel has pointed out, in the passage whose full meaning has been so strangely misunderstood. The moon at M gets but a small proportion of the rays carried around the earth in the way shown. In fact as we know that she subtends about 32' as seen from the earth, she only gets those rays, of the particular set illustrated above which are deflected within 16' on either side of 58',-that is, which are deflected between 42′ and 68′ (none are deflected between 68′ and 74', the necessary angle to just reach the lower edge of the moon from near a and the higher edge from near a'.)

If we suppose rays from the middle of the sun's disc (as seen from the earth or moon) dealt with in Fig. 2, it is easy to make the same figure by a slight addition illustrate the case for rays from points on the edge of that disc. For a line from the edge to E (that is, from either point on the edge of the solar disc in the plane of our figure) would be inclined either in direction Em or Em', where the angle mEm (bisected by EM) is the angle subtended by the sun's disc. We shall be near enough to the truth in putting m and m' on the outline of the moon at M. Then, drawing a complete set of rays for each or for either of instead of encumbering our figure and our minds by these directions, all we need do is to regard the set of rays already drawn as corresponding to either case, and setting a moon at m and at m' as shown. For either of these moons, the case is illustrated in which the particular point on the sun's surface dealt with lies at the edge of the sun's disc as seen from the earth or

moon.

Now in reality this-so far as a general explanation of the illumination of the moon's surface during totality is concerned ought to be enough. Sir John Herschel was content to give even less in the way of explanation and illustration. Yet he showed clearly enough all that is really essential.

But strangely enough this explanation has been altogether misapprehended. It has been supposed to show that the moon can receive scarcely any light from the sun by the actual deflection of solar rays towards her, insomuch that the light thus received counts for little or nothing compared with such illumination as the moon receives from our terrestrial twilight glow, from the burnishing of the edge of our earth's disc by solar illumination. That from the moon's surface situate as in Fig. 2, the sun himself is actually visible, so distorted and so reduced in apparent size that much less light than usual comes from him, but still that it is his very own self which is seen, as certainly as the setting sun is seen by

*

us after geometrical sunset is completed, this, which is really shown by the above explanation, remains with many a matter not only hard to see, but actually to be denied as absurd on the face of things.

The difficulty commonly presents itself in this way. If by the bending power of the earth's air rays from a particular part of the sun's disc are deflected to the moon, then rays from another part of the sun's disc must be deflected away from the moon; how then can all parts of the sun's disc be visible from the moon? Added to which comes another difficulty, based on a different misapprehension,-If light from every part of the sun reached the moon she would not be in eclipse at all, but shine as brightly as ever.

Let us see how the matter really is :

Fig. 3.

Suppose first that sa is a ray from the lowest point s of the sun S (lowest considered with reference to the figure) to the earth's atmosphere at a and so deflected as to pass to the moon at M. Then it is obvious that a ray s'a from the highest point s', will be carried as to m, and not reach the moon at all. But a ray from s' to some point b' in the atmosphere above a, will be deflected precisely to M. Thus an eye placed at M would see the part s' of the sun in the direction M b', and the parts in the direction Ma, and all intermediate points on the face sSs' in directions intermediate to Ma and Mb. Thus the diameter of the sun's disc from s to s' (the semicircle s S s' in reality would be transformed into a short straight line a b' on the edge of the earth's disc as seen from M. In like manner the same diameter of the sun's disc would also be transformed into a short straight line a'b on the opposite edge of the earth's disc, by rays following courses ranging from s'a' M to s b M. Imagining the plane of the figure to revolve on the straight line SEM, we get the same result for every diameter of the sun's disc,- -or the sun transformed into a ring around the earth, in the manner already dealt with (all but these preliminary and I had supposed nearly obvious considerations).

Here we have supposed the moon in apogee. If she is nearer the earth the point s on the sun will not be rendered visible by refraction at a, which would carry it above the moon. A ray from some point p, near to s would be so carried, and the arc p Ss' would be visible at a transformed into a straight line as a b', while a corresponding arc p'Ss would be visible at a' transformed into a straight line as a' b. The whole sun would be visible, but not every part of the sun doubly visible as in the former case.

These rays thus falling on the moon are rays of actual sunlight, not different from the rays by which we see the setting sun except in having some of them traversed a greater range of terrestrial atmosphere, and so having suffered more absorption, and making the ring into which the sun is transformed or distorted look, at least along its inner edge, much ruddier than our setting sun usually looks. I say some of them," because clearly the rays

*Geometrical sunset is completed when the sun's globe has passed below the plane of the natural horizon.

which like s'b' M have only traversed the higher regions of our air would not suffer absorption in anything like the same degree.

And here, in passing, let me remark that Mr. Ranyard's idea that the parts of our air above the highest range of clouds may be (or as he suggested must be) the parts chiefly acting in carrying sunlight to the moon during total eclipse, is inadmissible. The refractive power of air is nearly proportional to its density. At a height of 3 miles the air will not deflect the sun's rays more than 34', as already mentioned, and in central total eclipse this would not suffice to bring a ray of sunlight to the moon. For, as supposed to be geometrically measured from the moon (one cannot say "seen" because it would be hidden), the edge of the sun's disc at the time of central eclipse would be more than 40' from the edge of the earth's disc. Probably the highest part of the air effective at that time in bringing the sun into view would be not more than two and a half miles above the sea-level, and it could not be more than three miles. Clouds float much higher than that. If further proof were needed, it would be found in the ruddy colour of the eclipsed moon, which shows that usually the light she then receives has traversed the lower strata of our air.

This in reality is a sufficient solution of the problem of the ruddy-eclipsed moon. At least the solution is sufficient when combined with such an inquiry into the amount of illumination which the moon would receive, as I gave in former papers. What else I then wrote was chiefly an elaboration of the necessary part of the explanation, by an investigation of the actual nature of the distortions of detail which the sun's face would undergo. (To be concluded in our next.)

OPTICAL RECREATIONS.

BY A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY. (Continued from p. 270.)

(O far we have only spoken of light and darkness as the results of polarisation. It remains briefly to touch upon the gorgeous chromatic phenomena exhibited when light thus altered in its character traverses certain minerals and organic substances. We will, first of all, say something of the phenomena themselves, and then endeavour to afford, very shortly indeed, as much of an explanation of their cause as can be given without the employment of mathematics. The mineral known as Selenite will supply us with material for the experiments we are about to make. It is the crystalline form of gypsum (from which Plaster of Paris is made by burning it). Crystals of it are very common in the London clay of the Isle of Sheppey, whence we ourselves have obtained numerous specimens. Very well, then obtaining one of these crystals we shall find that it is of a slablike form, and is made up of innumerable thin plates, which may be split off with a sharp penknife. Let us remove as thin a slice as we can of this. Now, suppose that the rhombs in Fig. 47, the tourmaline plates in Fig. 48, or the mirrors in Fig. 49 (see ante, p. 197), are so placed that the image of the original source of light is extinguished, let us place our film of selenite between the polarizer and the analyser (in Fig. 49 A, it would be put through the slit S, square to the axis of the tin cylinder), and upon now looking through the second rhomb or slice of tourmaline, or

into our little mirror, C, we shall see the field lighted with the most lovely colours. We have said colours, because the chances are considerably against the beginner splitting off a film of identical thickness in all its parts from the selenite. Should he succeed in obtaining one of the same thickness throughout, then will the colouring of the field of view be homogeneous. In the first case, he will get patches of the most vivid and gorgeous yellow, blue, red, and green, &c.,-in the latter one of such colours alone. Now let us turn our analyser slowly round through 45°, and we shall find the colours, or colour, gradually fade until the light will pass through the film seemingly unaltered. Proceeding now to rotate the analyser through another 45°, the colours will begin to reappear, but they will be complementary to the original ones; that is to say, if the plate transmitted green light in the first position of the analyser, it will now let red light through. If it appeared blue originally, it will now seem yellow, and so on; the colours thus exhibited always being those which, mixed together, form ordinary white light. As the rotation is continued, the changes described will recur (of course, in reversed order) until the analyser has been turned 360° round the ray of light as an axis. Mica, if sufficiently thin, will exhibit similar phenomena, as will thin slices of quill or horn, tartaric acid crystallised on a plate of glass, the frost ferns on the window-panes in winter, and numerous other substances. Let us, in conclusion, see whether we cannot obtain some general idea of the manner in which these most striking and beautiful appearances are produced.

If we remove the analyser, and look at the beam of light proceeding from the polarizer through our film of selenite or other material alone, we shall see such light absolutely uncoloured. Hence it is obvious that the analysis of this whole light, or its separation into colours, is effected by the analyser. Now, selenite is a doubly refracting crystal, and when the polarised ray enters it, it is resolved into two rays, vibrating at right angles to each other. These rays are differently bent; and bending in a refracting medium means going more slowly, the ray which is the more bent being the tardier of the two. From this it will be readily seen that one of these rays may get half a wave-length, or any odd number of half-wave lengths, ahead of the other (Vol. VII., p. 321), and that, as formerly explained (loc. cit.), they may interfere. A little further consideration, though, will show that while these rays are composed of vibrations occurring at right angles to each other, it is physically impossible that interference can occur. But the analyser twists the two planes of vibration into coincidence, so that the waves can now destroy each other. Selenite, or any other doublyrefracting material, has, of course, a sensible thickness, and we have seen formerly (Vol. VII., p. 541) that waves of red light are much longer than those of blue. Consequently we shall require a thicker plate of selenite to retard the red rays sufficiently to extinguish them than we shall if we want to blot out the blue rays. Hence, when these longer waves have been neutralised by interference, the plate of selenite will shine with the colours produced by the shorter ones. Vice-versa, when the shorter waves have been annihilated, the longer waves will get through the analyser, and the colour of the field be derived from the less refrangible end of the spectrum.

Into the exquisite phenomena of circular and elliptical polarisation, it is impossible to enter here. An account of these must be sought in works specially devoted to the subject. All we have essayed to do is to introduce the student to the practice of some remarkable experi

ments which may be performed at little or no cost; and which serve to admit us to a nearer view of the intimate nature of Light.

THE

OUR HOUSEHOLD INSECTS. BY E. A. BUTLER.

HYMENOPTERA.

(Continued from page 264).

HE ants referred to in our last paper are genuine household insects, spending the whole of their lives in the shelter of our abodes, breeding amongst us, and bringing up their extensive families year after year in the same spot, as long as provisions are plentiful in the immediate neighbourhood. But this is not the case with the wasps, the next section of the Hymenoptera which will engage our attention. It is true that occasionally their nests are found in outhouses or lofts, or under the eaves of thatched roofs; but this is exceptional, and, as a rule, they enter our houses only in their adult condition; still, they are then such tiresome pests—at least, in imagination, if not always in reality-that we cannot forbear to grant them a place amongst our household

insects.

Notwithstanding the popular prejudice against wasps, there are many points of interest in connection with them. Their economy is remarkable, and inferior in interest only to that of bees and ants; their courage is certainly extraordinary; and though they are frequently an annoyance to us through their intrusive habits, yet there are, as we shall presently see, some counterbalancing advantages following from their mode of life; and, finally, their character is not really quite so black as it has been painted. That they are not, as some people seem to suppose, actuated by an irreconcilable hostility to human kind has been sufficiently demonstrated by observers who, like Sir John Lubbock, have closely studied their habits, and have found it possible to tame them and make pets of them, and to induce even such fiery-tempered beings calmly to feed out of their hands and to crawl over their persons without bringing their murderous weapons into requisition. Indeed, one observer, Dr. Ormerod, expressed his opinion that they are much less fickle and more reliable than bees-an opinion, however, which will probably not be generally endorsed.

and

They will rarely attack unless provoked, and, though it is not easy to maintain a philosophic composure indifference when a wasp is buzzing round one's head, yet such would no doubt be the best policy; at any rate, the violent flourishes and dashes so often made against them with handkerchiefs, knives, or what not are more likely to irritate than to drive away insects so renowned for valour. Of course, when we attack their citadel, they will at once assume the offensive (as who would not ?), and fight to the death for house and home. Very hot or windy weather, too, seems to bring out whatever spitefulness they possess, but this also is a psychological experience not altogether foreign even to Homo sapiens himself!

In distinguishing wasps from other Hymenoptera no reliance must be placed on the mere presence of yellow bands on the body, for though all wasps, of whatever habits, have these, such a style of ornamentation is by no means confined to them, but is of frequent occurrence throughout the whole order. But there is a certain peculiarity of the wings that will at once separate a wasp

All

from the crowds of other yellow-banded insects. wasps have four wings, and this will serve to distinguish them from certain two-winged flies of the order Diptera, with which they are sometimes confounded, but will not distinguish them from other Hymenoptera, as four is the natural number of wings in this group. But the anterior wings are folded longitudinally in repose, i.e., when a wasp closes its wings it not merely lays them along its back, as a bee would do, but also folds each fore-wing along a line running from its attachment to the thorax to the middle of the outermost or rounded edge of the wing (Fig. 1), the lower and more flexible part being bent

Fig. 1.-Wing of Wasp, showing line of folding.

under the rest, so that the wing becomes only half as broad as before.

In consequence of this peculiarity, the name Diploptera, or "doubled-wings," is given to that section of the order which contains all the wasps, and by this peculiarity they may at once be distinguished from all other Hymenoptera. One would naturally suppose that there must be some connection between this curious habit and the economy of the insects-something to account for so strange a departure from the general practice of the order; but if there be, it has yet to be discovered.

Our British wasps are of two totally distinct kinds. Those that usually obtrude themselves upon our notice are the social wasps, of the family Vespida, and, like the ants and other social insects, they exhibit the peculiarities of the three so-called sexes, the common abode, and the common labour for the common welfare. But besides these there are the solitary wasps, of the family Eumenida, which, from their habits of burrowing in sandy banks, are often called Sand Wasps and Mason Wasps. These have but two sexes, do not form large communities, and, after having provisioned their nest with food sufficient to last the whole lifetime of the larvae, leave their young to take care of themselves. They are less robust than the Vespida, and though still yellow-banded, have a much larger proportion of black about their bodies.

It is only very occasionally that we find solitary wasps in our houses; their young feed upon small caterpillars

young went through all their metamorphoses successfully, appearing in the kitchen when they had assumed the perfect form, to the no small surprise of its inmates.

In the keyhole of an eight-day clock-case, too, one family was brought up, appearing to be in no way disturbed by the ticking or periodical winding-up of the clock. They have also been found in the drawer of an old-fashioned looking-glass, in the folds of a piece of paper that had fallen behind some books, in hollow reeds used as thatch, and in the barrels of a pistol that was hanging invitingly on a post. In all these cases, accident furnished the insects with cavities ready made, and saved them the trouble of excavating their own burrows. These wasps are also sometimes seen in windows, buzzing about, apparently endeavouring to discover why a medium so transparent as glass should yet be able so successfully to bar their exit into the outer world.

The abdomen of an Odynerus is of a very curious shape. In all the wasps, the first segment seems more or less like a cap on the succeeding ones, but this is much more markedly the case in the solitary than in the social species. In the genus Odynerus the abdomen bears a ludicrous resemblance to a peg-top surmounted by a polo cap which is rather too small for it (Fig. 2). The second segment is of enormous size compared with the succeeding ones, and being very convex above, forms the head of the top. This segment is black, except the hind border, which is yellow, and the succeeding segments are more or less deeply margined with the same colour. The basal segment, i.e., the cap, is also furnished with a yellow marginal band, the shape of which is an important aid in the identification of the species. The folded wings and the top-shaped abdomen Fig. 2.-Abdomen are quite sufficient to enable any one to of Odynerus. recognise a sand-wasp.

The Vespido, or social wasps, which are much more frequently seen in our houses, we must reserve for the next paper.

(To be continued.)

THE YOUNG ELECTRICIAN.

BY W. SLINGO.

(Continued from p. 249).

life is to provide a stock of these, so that they have not the temptation to intrude on our privacy which the Vespido have, for the latter are almost omnivorous, and there are plenty of things in our houses which suit their taste admirably. The solitary wasps of the genus Odynerus do, however, sometimes construct their small nests in the most outlandish places. The nests consist of separate cells, each closed in and complete in itself, and devoted to the use of a single grub. Each contains an egg and a store of little caterpillars, each stung by the mother wasp sufficiently to prevent it from being at all lively, but not sufficiently to cause it to die and shrivel up.

These little clusters of cells have been found, amongst other strange places, inside the lock of a kitchen-door, where, notwithstanding the noise and disturbance caused by the passing and repassing of persons continually going in and out of the kitchen, the mother built cells for her brood, provisioned them, and sealed them up, and the

scopes there are one or two points that it will not do to overlook. Nothing was said in the previous article about a base for the instrument described, nor is it essential to have one, as it can be simply stood on the table, or any other dry substance. However, there is