counters by which the exchange of our ideas is facilitated, and by which we are enabled to store in the mind a much larger number of thoughts than would otherwise be possible, and to pass with much greater rapidity from one to another. Hence, we habitually think in words (suppressed sounds), a habit based upon convenience; but we also think to a large extent in visual images and imaginary movements; and this mode of thought is particularly noticeable in our dreams. This is the mode in which the lower animals think, and when a dog starts up in his sleep with bristling hair and barks, the inference is not unjustifiable that he is dreaming of combat with some imaginary enemy. There is such a thing as abstraction by way of visual or generic image that is to say, simple concepts may be formed by visualisation of similarities, and there is every reason to believe that animals possess this power of abstraction, as I have already shown. They abstract qualities common to various individuals; the dog has an abstract idea cat, as something possessing certain qualities which are obnoxious to him, and render the possessor a fit subject for him to persecute; and so with other animals whose ideas embrace not only individuals but also classes, they perceive resemblances and differences, and are thus enabled to recognise individuals as belonging to this or that class. Like the deaf-mute, the ordinary child begins thinking by this visual representation, and it is in this way that the deaf make their imitative signs. The visual images of these signs afterwards take their place in the mind as convenient representatives of thoughts, just as the audible images of words do in the minds of hearing people.

"There is nothing in mind which was not previously in sense," and the first thoughts are imaginary sensations. These sensations are grouped together, and forra what the psychologists call percepts. Afterwards the percepts. are associated with the expressions or symbols used to communicate them. Thus, hearing people, who are accustomed to express themselves in words, think generally in sounds, but frequently in visual images; while the deaf-mute generally thinks in visual images; and those who are both deaf and blind, in touches, tastes, and smells. As thought is primarily carried on in terms of sense, when one sense is cut off the others attain proportionately-increased activity.

Kruse, who was himself deaf and dumb, writing* about the mental development of his companions in affliction, says that the qualities which in his mind constitute the difference between things when he imitates objects and actions for the purposes of communication, become suitable marks which serve to fix them in his mind, so that he can memorise and recall them, and the signs thus become the means of thought.

On this point I have questioned several young people educated on the oral system, who, being perfectly deaf, have no idea whatever of anything like sound. At first my questions were misunderstood, and all asserted that they thought in words as we do. The hearing teachers also affirmed this of their pupils, and it was only with difficulty that I could make clear to them that, since our mode of thinking in words is simply thinking in sounds, it was impossible that the congenitally deaf could think in this way. After minute questioning, a fairly intelligent girl, 18 years old, maintained that she ordinarily thinks in signs or imaginary actions. That when she thinks of anything in reference to the deaf and dumb, she thinks in actions; but that when she thinks of * "Ueber die Taubstummen."

hearing people, she thinks in words that is to say, in certain groups of movements of the vocal organs, not in words as written or printed, although she reads and writes extremely well. A bright deaf boy of fourteen, taught on the oral system, told me that he thinks in words as spoken by himself, which means, of course, in certain groups of movements by which he is accustomed to express himself, but which we interpret by the sounds produced. Several others agreed that they think in the same way, but that the thought appears sometimes as written, sometimes as spoken by them or by other people. When they think of words as spoken by the mouth of another that person is the one with whom they chiefly converse, generally the teacher, which again illustrates the force of habit in regulating the mode of thought.

The form of dreams is important in illustrating the habitual mode of thought: thus it is believed that animals think and dream in visual images. In the dreams of those deaf and dumb who are taught on the old system of dactylology finger-twists play a large part. When Laura Bridgeman was asleep her fingers were frequently seen moving as in animated conversation, and deaf children taught on the oral system speak in their dreams. Thoughts are not bound down to any one set of signs, whether verbal or otherwise; but certain signs, which to the thinker are marks, mental shorthand notes, so to speak, are adopted in preference to others, owing to custom and conveniA man cannot be said to know a foreign language thoroughly until he comes to think in its forms, instead of merely translating into them his thoughts from his native tongue. When he has accomplished the former, he will have so thoroughly assimilated the foreign tongue that he will dream in it. A French gentleman resident in England tells me that, for the first twenty years of his residence, he always dreamed in French, but that he now habitually dreams in English, the habit of thought of his later life having overcome that of his youth.

ence.

Although thought in its higher phases is to a great extent dependent upon language by means of which it is. chiefly developed, thought must historically be anterior to language. Generals and particulars are apprehended, comparisons, distinctions, and inferences, made remembered, and applied without the use of language both by the lower animals and by men.

The case is clearly and humorously stated by Professor Whitney, who says: "To maintain that the idea waits for its generation until the sign is ready, or that the generation of the idea and of the sign is a simple and indivisible process, is much the same thing as to hold, since infants cannot thrive in this climate without clothing and shelter, that no child is or can be born until a layette and nursery are ready for its use, or that along with each child are born its swaddling-clothes and its cradle." He continues: "The mental act is momentary, its formulation in words occupies time; we have our thought to start with and then go on to give it deliberate expression. The operation of thinking in words is a double one; it consists of thinking and of putting the thought into words; we conceive the thought and conceive also its expression. That when we turn our attention full upon our own minds, we read there the act and its expression together does not necessarily prove more than the intimacy of the association we have established between our conceptions and their signs, and the power over us of the habit of expression. Every

* Whitney's "Language and the Study of Language," p. 412.

deliberate thought doubtless goes through the mind of the deaf-mute accompanied by an image of the dactylic writhings which would be his natural mode of expressing it; but his mental action is not slavishly dependent upon such an external auxiliary."

That we deliberately clothe our thoughts in words according to the double process here described is undoubtedly true of a great number of thoughts; but in a vast number of cases words are present in the mind as marks of thoughts which it is unnecessary to call up in full, and these words are used as stepping-stones from one reasoning to another.

1. Ursa Minor, the Little Bear (a, the Pole Star). 2. Draco, the Dragon (a, Thuban)

3. Cepheus, King Cepheus. 4. Cassiopeia, the Lady in the Chair.

5. Perseus, the Champion (ẞ, Algol, famous variable).

6. Auriga, the Charioteer (a, Capella)

7. Ursa Major, the Greater Bear (a, ẞ, the Pointers).

8. Canes Venatici, the Hunting Dogs (a, Cor Caroli).

9. Coma Berenices, Berenice's Hair.

Queen

22. Cancer,

the Crab (the cluster is the Beehive). 23. Leo, the Lion (a, Regulus). 24. Virgo, the Virgin (a, Spica). 25. Libra, the Scales.

26. Ophiuchus, the Serpent Holder.

27. Aquila, the Eagle (a, Altair). 28. Delphinus, the Dolphin. 29. Aquarius, the Water Carrier. 30. Pisces, the Fishes.

31. Cetus, the Sea Monster (o, Mira, remarkable riable).

va

32. Eridanus, the River. 33. Orion, the Giant Hunter (a, Betelgeux; ß, Rigel).

34. Canis Minor, the Lesser Dog (a, Procyon).

35. Hydra, the Sea Serpent (a, Alphard).

36. Crater, the Cup (a, Alkes). 37. Corvus, the Crow. 38. Scorpio, the Scorpion (a, Antares).

39. Sagittarius, the Archer. 40. Capricornus, the Sea Goat. 41. Piscis Australis, the Southern Fish (a, Fomalhaut).

42. Lepus, the Hare. 43. Columba, the Dove. 44. Canis Major, the Greater Dog (a, Sirius). 45. Argo, the Ship.

INEFFICACY OF THE EUCALYPTUS.-Notwithstanding the positive statements that have been made as to the suitability and value of plantations of Eucalyptus globulus in swampy and marshy districts, some scepticism has been manifested upon the point, and some time since a paper attributed anything but favourable results to the experiments made in this direction in Italy. In a recent report on the Lucknow Horticultural Gardens (Gard. Chron.) Dr. Bonavia records a similar experience, and expresses a wonder that the tree should have ever been thought suited for the purpose for which it has been claimed to be efficacious.-Medical Press and Circular.

* "Indeed, I know that the children of the late Principal of the Hartford Deaf and Dumb Asylum, who had grown up in the asylum, and knew the peculiar language of the inmates as familiarly as their English, could always tell what their father was thinking of, as he walked up and down in meditation, by watching his hands: his fingers involuntarily formed the signs which were associated in his mind with his subjects of thought; while, at the same time, doubtless, he imagined also their spoken signs" (p. 213).

MR.

LIGHTNING.

BY W. SLINGO.

R. PROCTOR, in his "Gossip" a fortnight since, demonstrated very simply and clearly the inability of an observer to determine the direction, whether from cloud to earth or earth to cloud, of a lightning flash. This is a fact the truth of which I anticipated, although I did not essay to prove it, in my article on "The History of a Lightning Flash" (KNOWLEDGE, No. 146.) I might now, perhaps, venture on a presentation of the proof in a manner differing from the process adopted by Mr. Proctor, but I take it that such a course is, under the circumstances, unnecessary.

There still remains, however, the question, Can or does, a lightning-flash strike upwards? This question I in part answered in the above-mentioned article, by observing that "it is just as likely that a discharge may travel upwards as downwards." It is to present an answer to this question that I am now writing.

In the first place, we are aware that the atmosphere is sometimes positively, at other times negatively, charged. If, therefore, we determine in our own minds that the discharge can only take place in one direction, positive to negative, or, conversely, negative to positive, then it is clear we must concede the possibility of a discharge from the earth as well as to it. Now, however great may be our reverence for the single or double fluid theories, neither of them is capable of helping us. By the single-fluid theory, the discharge should always be in one direction (electrically speaking). But the adherents of this theory are unable to determine to their own satisfaction whether the plus or surcharge exists in the positive or negative state. While it has generally been claimed that a positively electrified body has an excessive charge, there are not wanting those who maintain that this excessive charge belongs to the negatively electrified body. By the double-fluid theory we are asked to believe that when a discharge takes place it is accomplished by the mutual exchange of a portion of the charge on each of the oppositely electrified bodies. Now this would mean that a discharge of positive electricity should take place from the positively to the negatively charged body, and that at the same time a discharge of negative electricity should travel from the negatively to the positively charged body. This, if it means anything, means that two distinct discharges, starting simultaneously from the two charged bodies, are necessary to produce a state of neutrality. But, inasmuch as the performance of work

is inseparable from time, small though the lapse of time may be, it follows that the loss of, say, positive electricity on the positively excited body would not coincide exactly with the accession of the corresponding amount of electricity necessary to produce neutrality. In other words, when the two bodies are separated by a medium of considerable extent, there should, at each surface, be two flashes of light travelling in opposite directions and capable (with the aid of suitable apparatus) of being distinguished.

Let us call to our aid the (what I may style classical) experiment of Sir Charles Wheatstone. The accompanying diagrams illustrate the experiment. P and N (Fig. 1) are two pieces of metal separated by a glass plate or

August 8 at 8 o'clock. August 12 at 8 o'clock.

other insulating substance, G. Wheatstone used a Leyden jar, his object being to ascertain the speed at which electricity travelled. But any other form of condenser will answer equally well. Let us conceive the metal plate P to be charged positively, and connected to the ball A, while the plate N is charged negatively, and connected to the ball F. Close to A, but not touching it, is the ball B, which is connected to the ball C by means of a quarter of a mile of wire. Close to C, but not touching it, is another ball D, which is likewise connected, by means of a similar length of wire, to the ball E. This, in its turn, is placed close to, but not touching, F. There are thus three pairs of balls, and in the event, therefore, of the charged plates PN being

discharged, three sparks will be seen between these balls. Looked at under ordinary conditions, the three sparks will appear simultaneously.

Opposite the balls, however, was placed a revolving mirror, making 800 revolutions per second, and the images of the sparks received by it were reflected on to a screen. It was observed on discharging that the images appeared in the manner shown in Fig. 2, A and F being simultaneous, while C was a little later. The retardation of the middle line or spark was calculated to amount to one 1,152,000th of a second; that is to say, this was the time taken by the discharge to traverse the quarter of a mile of wire between B and C or E and D, corresponding, in this particular case, to a velocity of 288,000 miles per second. From the lengths of the arcs, which were in all three cases identical, it was calculated that the duration of each spark was one 24,000th of a second. Had the discharge travelled from the positive plate P to the negative plate N, then a flash of lightning would have been seen pictured on the screen between each pair of balls, that between A and B occurring first, and the other two following in rapid succession. Had the discharge Had the discharge started at the negative plate the flashes would have been seen in the reverse order. Had there been (on the double-fluid hypothesis) a mutual exchange, Wheatstone would have observed, not three, but at least five sparks pictured, two occurring between A and B, two between F and E, and one between C and D.

The evident teaching of this experiment is that a lightning discharge may start from earth and cloud simultaneously, meeting at some central point. But are we justified in inferring that it always does so? I think not. I rather imagine that in the majority of cases the conditions are not altogether comparable with those of the experiment. The whole matter turns upon the question of electrical "tension," a term which may be defined as the tendency to produce an electrical discharge. Where, over a given area, there is the greater concentration of electricity, there will be, perforce, the greater tension. The distribution of electricity on a conductor is rarely uniform, varying very considerably with the shape. Where the greater prominences occur, there will be found the greater concentration of electricity, whence it is said that electricity accumulates at points; and it is well known to the merest tyro in electrical science that this concentration at points results in a proportionally increased tendency to produce a discharge. If, then, a certain quantity of electricity is confined to a cloud, and that quantity, acting inductively upon the subjacent earth, produces an equal degree of electrification (of the opposite kind), it follows that, in the majority of cases, the charge on the cloud will be at a greater tension than that on the earth, for the simple reason that, more often than not, the cloud is more pointed or irregular in shape than the earth. As a matter of fact, the terrestrial charge is more or less uniformly distributed throughout the neighbourhood, while in the cloud there is a considerable concentration at the edge or pointed portion. Whence it ensues that, in the majority of cases, there is great reason to suppose that the discharge strikes downwards only. On the other hand, were the terrestrial surface provided with but a single point, such as is furnished by the well-known lightning protector, the discharge would only take place upwards. Moreover, the discharge would be a gradual, or, within certain limits, a continuous one, because the tension would grow so rapidly (as the cloud approached) that it would be quite incapable of retaining the charge. Had Wheatstone been able so to modify his experiment as to place

at A or F a huge sphere, or even a plate instead of a small ball, and, conversely, to substitute for For A a still smaller ball approaching even a point, there is to my mind little doubt but that he would have seen a different result. He would in all probability have obtained the sparks in succession, that near the small ball first, followed by one in the centre, and another striking the large surface. Now neither the single nor the double-fluid theories can adequately account for this.

We may, however, regard the charged cloud and the subjacent electrified earth as the extremities of a long elastic chain of electrically-polarised particles, each subjected to a series of stresses increasing in strength until it is compelled to yield. This chain, indeed, strives to shorten itself, and it is this striving that we know as electrical attraction. With the necessary facilities this shortening takes place, chief amongst these facilities being the physical elasticity or mobility of the intervening substance (or di-electric)—in this case, air-and the low electrical capacity of the charged bodies.*

We may compare the polarised chain to a rod of extended elastic held at the extremities until the extension is sufficiently great to overcome the holding or restraining power. restraining power. If two oppositely-charged bodies have equal capacity, we can conceive that, when the discharge occurs, it will bear some resemblance to a piece of extended elastic set free at both ends simultaneously. This is exactly what happened in Wheatstone's experiment. Where the two bodies have different capacities, we may compare the polarised chain to a piece of elastic held more firmly at one end than at the other, whence it follows that the contraction will be one-ended, that which is less securely held corresponding to a charged body of small capacity, and which, therefore, speedily attains to the tension necessary to produce discharge.

In conclusion, then, the lightning discharge may take place (i.) simultaneously from earth to cloud and cloud to earth, (ii.) from earth to cloud, (iii.) from cloud to earth. The first form happens when the configuration of earth and cloud are (electrically) similar; the second when the earth is sharper than the cloud; the third when the cloud is more pointed than the earth, and it is this third form which I think most frequently ensues.

RAMBLES WITH A HAMMER.

BY W. JEROME HARRISON, F.G.S.

FROM NUNEATON TO TAMWORTH-THE WARWICKSHIRE COAL-FIELD.

BUT

(Continued from p. 21.)

UT we have not yet seen the finest exposure of the Cambrian shales. If, on leaving Hartshill, we direct our steps in a south-westerly direction to Stockingford Station (2 miles), and then walk along the Midland line to Nuneaton, the following facts may be observed. Soon after leaving the station we note on the left-hand side of the line a large brick-pit, showing coalmeasure shales and sandstones dipping at high angles to the south-west, and much disturbed, indicative of a fault (missed by the surveyors), which runs between the coalmeasures and the Cambrian beds beneath. This line of

* Capacity is measured by the quantity of electricity required to raise the charge on a conductor to a given potential. A body which has the highest capacity is that which combines minimum surface with maximum content, viz., a sphere. In a body having, therefore, large capacity we should get low potential.

fault is actually indicated on the surface by the number of brick-pits which work the "fault-stuff," as the rubbed-up clayey matter between the two sets of rocks may be called; moreover, all the diorite bands end abruptly against it. Proceeding eastward, we enter a cutting in which the Cambrian shales are capitally exposed. They consist of grey, black, and purple to red shales-the latter lying at the base. They dip to the south-west at from 55° to 65°, and the height of the cutting is from 20 ft. to 30 ft. Nodules of manganese occur in the red shales, and they were formerly worked for this mineral at several points near Nuneaton and Hartshill. Fossils occur in the shales, but they are indistinct and difficult to find. The commonest shells are small species of Lingulella and Obolella, and with these are trilobites of the genus Agnostus. The collection of life-forms-such as it is-appears to place the strata near the base of the Tremadoc Slates-a division of the Upper Cambrian formation finely developed in North Wales. If this correlation be correct, the Hartshill quartzite probably represents some portion of the Lingula flags, which in Wales lie below the Tremadoc slates, just as the Hartshill quartzite lies below the Stockingford shales.

South of Nuneaton the quartzite is not seen, but the overlying shales can be traced past Chilvers Coton through Griffin Hollow to Marston Jabet. At the latter village in an old quarry near the Hall-the shales are seen to dip east, at a low angle. They are here traversed by an intrusive mass of diorite, which forms two large bosses north-west of Marston Hall. The same easterly dip is found at the other end of the strip of Cambrian strata, north-west of Atherstone, where the beds-coalseams and all-roll over and dip to the east.

Thus the north-east border of the Warwickshire coalfield is formed by a narrow fringe of Cambrian and PreCambrian strata, which rise up sharply from beneath the Coal-Measures (from which they are separated by a line of fault), and occupy a tract of country nine or ten miles long by from half-a-mile to a mile in width. The structure of the region is that of an anticlinal, broken through by a fault in the centre, between Nuneaton and Atherstone, but preserving its crest to the south and to the north of these towns.

So far we have been concerned only with the eastern side of the Warwickshire coal-field. It is now time to turn our attention to the western boundary, the distance between the two being only from four to six miles. (Fig. 2.) The line from Birmingham to Derby runs parallel to the western outcrop of the coal-seams, and by walking from Kingsbury to Fazeley (little stations, the former five and the latter a mile or so, south of Tamworth), the principal facts can be seen in a few hours.

a fault from the Coal-measures. The latter are well exposed in a long cutting, in which five distinct seams of coal can be recognised as black stripes between the beds of blue shale and sandstone. The strata dip eastward at a very high angle-70° to 80°-so that in several of the collieries the coal-seams have been followed from their outcrop almost vertically downwards to a considerable depth. The colliery - workings follow the coal- seams eastward, but in a westerly direction the lowest seam is broken and lost against the Cambrian strata, which here, as on the eastern boundary of the coal-field, have been thrust up along a line of fault. After examining the railway-cutting-which is entirely through the coalmeasures-we turn to the left (westward) to study the Cambrian strata at Dosthill. Here there are several exposures in field - pits, brick works, &c., of grey and black shales, which are traversed by countless numbers of worm borings, SO that one is tempted to refer the strata to the "annelidean stage " of the Cambrian epoch. The river Tame flows from south to north through alluvial flats along the western foot of the bold short ridge on which the village of Dosthill stands. The hard, dioritic rock rises so abruptly from the stream-course that at places the hill-side is nearly vertical; other igneous rocks here are dykes of a greyish decomposed rock, similar to those near Nuneaton. In a field-pit quite close to the high-road (on the west side), three-quarters of a mile due south of Dosthill Church, there is a very interesting section, showing a "neck" of igneous rock rising through the shales, and then spreading over them in all directions. In this respect, it is almost unique in the Midland counties (Fig. 3).

Fig. 3.-Trappean rock breaking through Cambrian shales at Dosthill, near Tamworth.

Standing on the summit of Dosthill the geological structure of the region can be taken in at a glance. The rocks at our feet dip eastward, to rise again in the Hartshill ridge. The coal-field lies like a wedge between two faults, which meet at Spring Coppice, five miles northeast of Dosthill, but which diverge as they extend southward. All the region between these two faults has been uplifted from 1,000 to 6,000 ft. Formerly it was covered, and the coal seams were concealed by a considerable thickness of triassic marls and sandstones; but these have been stripped off the uplifted area by rain and rivers, by frost and ice, and by the sea. But beyond the lines of fault-to the east and to the west, to the north and to the south-the red rocks encircle the coal-field. Beneath these triassic strata, in certain, though not in all directions, the coal-seams now lie at great depthsburied treasures which have been eagerly sought for by capitalists, who, availing themselves of the latest scientific improvements, have bored down more than a thousand feet in search of those "black diamonds" which some ten years ago were in such great demand, and which are absolutely necessary to almost every industry in this country.