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galvanometer 812, which means a very large current, and at 81° it kept it for hours. It remains ready for action at all times, and the heavy

LIEUTENANT-GENERAL HUTCHINSON'S PROPOSED NEW RAILWAY SYSTEM. EFLECTION will show that coning of the

sulphate of zinc, as it is formed, sinks below the It will be understood that during every revolu- wheels of railway carriages is so far wrong

silver and leaves the solution active for a prolonged period, and may be drawn off by a syphon at intervals, and replaced with fresh acid solution without wasting the upper portion. This perfect cell has been too recently made to enable me to give all its results, but a much smaller one, and one not so fully developed, and contained in a quart jar, gave 78°, and after use for several days steadily in electrotyping, and three weeks irregular experimental work, gave 62°, having had had nothing done to it meanwhile. So powerful is this cell, that after the introduction of a porous jar to contain the zinc, it gave 76°, and with common salt substituted for acid in the porous jar it gave 63; for many purposes it might be so worked, as cast zinc might then be used, the local action being lessened; in such case, as wide a porous jar as possible should be used, and its contents replenished at intervals when required. (To be continued.)

MECHANICAL MOVEMENTS.*

(Continued from page 124.)

motion, at a uniform velocity of the screw D, carrying the eccentric cone, gives a series of changes of velocity and direction to the roller C. tion of the cone the roller would press against a different part of the cone, and that it would describe thereon a spiral of the same pitch as the screw D. The roller C would receive a reciprocating motion, the movement in one direction being shorter than that in the other.

64. Two worm-wheels of equal diameter, but one having one tooth more than the other, both in gear with the same worm. Suppose the first wheel has 100 teeth and the second 101, one wheel will gain one revolution over the other during the passage of 100 x 101 teeth of either wheel across the plane of centres, or during 10,100 revolutions of the worm.

a

65. Variable motion. If the conical drum has regular circular motion, and the friction-roller is made to traverse lengthwise, a variable rotary motion of the friction-roller will be obtained.

66. The shaft has two screws of different pitches cut on it, one screwing into a fixed bearing, and the other into a bearing free to move too and fro. Rotary motion of the shaft gives rectilinear motion to the moveable bearing, a distance equal to the difference of pitches, at each revolution.

67. Friction pulley. When the rim turns in the opposite direction to the arrow, it gives motion, to the shaft by means of the pivoted eccentric arms; but when it turns in the direction of the arrow, the arms turn on their pivots, and the shaft is at rest. The arms are held to the rim by springs.

68. Circular into reciprocating motion by means of a crank and oscillating rod.

69. Continued rectilinear movement of the

A COMBINATION movement, in which 61. the weight moves vertically with a ich ciprocating movement; the down-stroke being shorter than the up-stroke. B is a revolving disc, carrying a drum which winds round itself the cord D. An arm C is jointed to the disc and to the upper arm A, so that when the disc revolves the arm A moves up and down, vibrating on the point G. This arm carries with it the pulley E. Suppose we detach the cord from the drum and tie it to a fixed point, and then move the arm A up and down, the weight W will move 70. Anti-friction bearing for a pulley. the same distance, and in addition the movement 71. On vibrating the lever to which the two given to it by the cord, that is to say the move-pawls are attached, a nearly continuous rectilinear ment will be doubled. Now let us attach the motion is given to the ratchet-bar. cord to the drum and revolve the disc B, and the weight will move vertically with the reciprocating motion, in which the down-stroke will be shorter than the up-stroke, because the drum is continually taking up the cord.

62 and 63. The first of these figures is an end view, and the second a side view, of an arrangement of mechanism for obtaining a series of changes of velocity and direction. D is a screw on which is placed eccentrically the cone B, and C is a friction roller which is pressed against the cone by a spring or weight. Continuous rotary

Extracted from a compilation by Mr. H. J. Brown, Editor of the American Artisan.

frame with mutilated racks gives an alternate rotary motion to the spur-gear.

72. Rotary motion of the bevelled disc cam gives a reciprocating rectilinear motion to the rod bearing on its circumference.

73. Rectilinear into rectilinear motion. When the rods A and B are brought together, the rods C and D are thrust further apart, and vice versa. 74. An engine-governor. The rise and fall of the balls K, are guided by the parabolic curved arms B, on which the anti fraction wheels L run. The rods F connecting the wheel L with the sleeve move it up and down the spindle C D.

75. Rotary motion of the worm gives a rectilinear motion to the rack.

(To be continued.)

in principle that it militates against progress in proportion to the extent of the coning.

The plan was originally designed in order that at curves centrifugal force should be met by wheels higher on the outer rail than on the inner, and that the wheels running over the greater distance (the outer curve) should virtually have a larger diameter than the inner wheels running over a less distance (the inner curve). The incorrectness of this reasoning is evinced by the fact that, owing to centrifugal force, the tendency of the carriage is to run in a tangential direction (calculated from the centre of the carriage), thereby forcing the outer leading wheel against the outer rail-the inner near wheel against the inner rail.

That coning wheels is mathematically opposed to progression, and occasions much waste of steam power, is manifest (for it is a drag on every carriage) when we consider that the wheels of all railway carriages could be coned to such an angle with the horizon that the lateral presauteng with the rail would extend the prical pressure on it, thus producing a jamb, and that the less the angle the less would be the jamb-in other words, the less the coning the less the resistance to progress. It thus becomes evident that no wheel would so little resist progress as the cylindrical.

With wheels coned merely to an angle of 5° with the horizon, the increase of draught

W

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=

0873 W representing the weight of the carriage.

When it curves, or from swaying to the right or left, the carriages shift to the part coned to 45° near the flange, the draught is doubled. The pressure (the horizontal pressure) varies as the tangent of the angle that the coned surface makes

with the horizon.

Moreover, this constant resistance to progress from constant lateral pressure is yet further increased when the carriages, by swaying from side to side, cause one wheel to run up hill, the opposite wheel down hill, thereby creating jerks and mental to comfort, and as injurious to the peroscillations, especially at high velocities, detrimanent way as to the rolling stock-exacting, moreover, unnecessary demands on the steam

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power-" unnecessary' "because they would not be exacted by unconed wheels.

To ascertain the exact breadth of the wheels, of the ordinary radius of 20 chains, the breadth let the breadth of half the axles of the several of the broadest wheels needs be no more than 6in wheels (exclusive of the allowance for width of beside the width of rail and the usual inch rail and " play ") be respectively represented by for "play." The projection of the broad st D D, DI, &c., placed respectively at distances C wheel outside the rails could never exceed C, C, &c., from the centre of the chord (the 34in. centre of the wheel base).

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These considerations predisposed us to wish success to any proposition for safely substituting cylindrical for coned wheels, and we feel bound to say that we think the inventor has designed a plan that will be found of great advantage to future lines. By his making the carriages run Let G represent the width of the gauge, on many wheels, the rails may be made lighter R represent the radius of the curve of rail. than is usual, for it is nowhere strained by a Then great weight on any one spot, and by his giving D = (as shown on the curved line of rail, Fig. 2 in -R2 (RG) the woodcut) an increased breadth to the central DI = ✓CR (R — G) wheels, proportionate to the severity of the D = CR curve, carriages can travel at the greatest speed (RG) &c., round a circle whose radius (as is well exempli&c., &c. fied in a model he has made) little exceeds their Only the wheel base (the chord) lying within wheel base-for the outer edge of the broad the curve has been spoken of. It is evident that wheels is at the severest curves supported by the the wheel base can be extended at both ends on rail, thus ensuring safety by virtually enlarging the prolongation of the chord beyond the curve. the base. In other words, the more centrifugal Wheels placed on this prolongation prevent any force acts upon the carriage, the wider is the overhang. The less abrupt the curves the part of the base which resists its displacement. greater might be the number of wheels.

The chord (movable) of the curve may be regarded as the true rigid wheel base of the carriage. All the axles of the wheels are at right angles to the chord, and in every instance half the breadth of each wheel equals in length the part of the line, in the vertical plane of the axle, intercepted between the chord and the arc. To the full breadth must be added, as before stated, the breadth of the rail, and about lin. for "play."

It is mathematically correct that, regarding the part of the radius intercepted between the centre of the chord and the arc as unity of any measure, the diameter of the circle is equal to the square of half the chord expressed in the same measure plus 1.

The breadth given to the wheels would not lead to increased width at cuttings. At extremely severe curves the rail would be laid down close to the outer edge of the curve. With the curves

The less acute the sharpest curve, the less need be the width given to the wheels, and the greater might be the length assigned to the wheel base within the curve, as well as without the

curve.

The constructor of the locomotive would have to devise a somewhat different arrangement than is usual for some of its parts, but one quite feasible, to give room for the wide tires of the central wheels. It would be simpler than any double "bogie" carriage, from all the axles being parallel.

The parallelism of the axles would never have been found objectionable had it not been for the coning, and the grinding of the flanges against the rails. In many countries the whole of the common carts still continue a fixture to the axle, yet with heavy loads they easily turn corners where the outer wheel has to travel over a space many times exceeding the distance traversed by the inner. With the very unusual sharp curve of a 5 chain radius (110 yards) measured from the outer wall-in a curve of of a circle-the gauge being 4ft. between the centre of the rails, the outer wheels only run over 2:3562 yards more than the inner. Manifestly, therefore, the evil arising from the difference in travel of the wheels

of unflanged cylindrical wheels is more imaginary than real,

When a carriage is stationary, the perpendicular line in the vertical central longitudinal plane of the axle intercepted between the point of contact of the cylindrical wheel with the rail, may be regarded as the spoke of a wheel (the spoke on which the carriage rests). During one revolution of the wheel such imaginary spokes are endless in number-ever of the same length in cylindrical wheels, but of constantly varying length in coned wheels, as well as of varying inclination from the perpendicular, according to the degree of coning.

These points of contact (especially on the inventor's suggested light, deep, narrow rails) must be very small, therefore the change of the imaginary spokes from their one plane at right angles to the axle, to the unresisted spiral rotation necessary when the direction of the rail alters, cannot retard the rotation of the wheel (cannot retard progress), for each successive spoke still revolves in its own plane at right angles to the axle. On straight lines of rail, and at regular curves, all the imaginary vertical axles of each wheel rotate in one plane ever at right angles to the axle.

The 10 pair of wheels shown (Fig 1) in the representation of the locomotive (which is about double the ordinary length) are driving wheelsall have the same diameter, and all the pistons the same travel. The area of the piston of the eentral cylinder is of course about larger than the pistons of the cylinders at the extremities, as it drives 4 pair of wheels-the others only 3 pair. Should there be a practical difficulty, which is not apprehended in making the one piston (with its double rod) both pull and thrust, and the 4 pair of wheels work harmoniously together, there might be two pistons in one cylinder, or two cylinders.

the broad wheels shall be further increased by a constant escape of sand between their surfaces during ascents.

it

W

Ptan..

2

W =0- =

2

As the carriages run either end foremost, should so happen in a line of railway that all the sharpest that is, there is no horizontal pressure. curves between the two termini ben the same way, it evidently would diminish the width necessary for the broad wheels, were the wheels so fixed to the carriages that, when running on a straight line, the centre of the wheels would not be on the rail, but lie a little outside of it towards that side of the rail where the principal curves bend outwards.

If @ 90°, that is, if the wheel were simply ver

tical, and had no horizontal surface (an imaginary case)

The curves on most of the railways in England are so wide that (without altering the rails), by giving the proposed additional breadth to the wheels, a greatly increased length could be easily given to all the carriages, therefore to the boiler, with a central fire, consequently augmented steam power to the locomotive; besides the increased holding power acquired by being enabled to place a greatly increased weight over the many driving wheels, and so making every locomotive a tank engine.

The working portion of the locomotive towards the centre and rear could be covered in to prevent injury from dust, not that it injures the machinery of the Fairlie, though its parts are more complicated.

'P = tan 90°

W

2

W =α2

that is, the horizontal pressure is infinite.

If = 45°, that is to say, the wheel be coned to 45°
W
Ptan 45°

2 W W

= 1 x

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5 chain radius = 110 yards Diam. yards. yards.

220 x 31416 = 691 152, length of outer circle. 217 x 31416 = 6817272, length of inner circle. Difference 9.4248

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As nearly £500,000,000 have been expended on railways in the United Kingdom, we cannot think, however great might be any suggested improvements, that a rapid change would be made in a system on which such vast sums have been spent. We are, however, mistaken if the and present proposal be not gradually adopted in this country, and if those on whom will devolve the responsibility of constructing future lines abroad, in the most safe, economical, and durable manner do not follow a plan which we hold to be correct in principle, and may be improved on in the minor details. It is as applicable to the the means of ascending very steep gradients, hanlage narrowest as to the widest gauge, and as it gives

As regards progression, it seems undeniable that cylindrical wheels must donyand less hand in

"bogie" frames, and the inventor retains them on the line by means as little opposed to progress as can be imagined-viz., by guide wheels that have no other duty to perform than, on a straight line, to occasionally touch and rotate in a vertical plane against the vertical side of the rail, and at curves to act against the side in the direct manner that the cylindrical supporting wheels act on the upper surface.

These deeply-flanged guide wheels (Fig. 8) are placed at the extremities of the wheel base (within the curve), and sustain no more of the weight of the carriage than suffices, by means of a screw, so to press them down, that however sudden may be any sinking in the rail, the wheels follow it, and cannot get displaced. Through a horizontal movement (equal to the extent required by the severest curve) they, readily adjust themselves to the course of the rail, for the great length of the stem (playing in the tube strongly fixed to the carriage) saves them from any severe lateral pressure at top. In cases of difficulty this wheel seems much safer than the ordinary wheel, which, owing to the coning, has a bias to run upwards over the rail.

The wheels b and i are supposed to have flanges, which, however, are never called upon to act unless through some unlikely chance the guide wheels should get out of order, when as regards safety the carriage would be on a par with those now running.

It is evident that the diminution of haulage, consequent on the employment of cylindrical unflanged wheels solely to support, and of guide wheels solely to direct, must effect a valuable saving of steam for the substitution is made in every class of carriage.

The inventor says that the correctness of the principle would be inexpensively tested on any line by firmly joining three passenger carriages together supported on unconed wheels, and fixing vertical guide wheels (Fig. 8) at the points of junction. This triple carriage to be connected with the adjoining by the buffer bar described in the patent.

The inventor has designed other guide wheels (Fig. 9), which lie in a plane inclined to the horizon, and readily pass through the openings at guard rails and switches, but we are of opinion that the vertical will be the most liked.

The reservoirs containing a lubricant are marked t..

It is part of the proposed system that the rails on steep inclines shall be of great breadth, and that the friction (holding power) between them and

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COLOUR AND COLOUR BLINDNESS. BY "OMICRON."

(Continued from page 122.)

colour is accounted for by the frequency of the vibrations, or the number of impulses made on our nerves in a given time by the ethereal molecules next in contact with them, precisely as in the doctrine of sound the frequency of the aerial pulses, or the number of excursions to and from its point of rest made by each molecule of the air, determines the pitch or note.* The shortest wave produces violet light; the longest, red. Sir John Herschel has composed the following table, in which he gives the length, and the rapidity of the coloured rays of the spectrum, assuming the velocity of light to be 192,000 miles per second :

N the undulatory theory of light, difference of

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From this table we see that the sensibility of the eye is confined within much narrower limits than that of the ear, the ratio of the extreme vibrations being nearly 1:58:1, and therefore less than an octave, and about equal to a minor sixth. That man should be able to measure with cer tainty such minute portions of space and time is not a little wonderful, for it may be observed, whatever theory of light we adopt, these periods, and these spaces, have a real existence, being in fact deduced by Newton from direct measurements, and involving nothing hypothetical, but the names here given them. What marvellous mechanism must pervade Nature, to see in the flashing of an eye the innumerable and varying hues with which the earth is carpeted, the birds gorgeously plumed, and that distinguishes the races of animals and man!

But an acute discrimination of colours is not given to all alike, and we do not speak here of the effect that education in colour produces on

is a constant, the value of P varies with the the eye, but the natural inability that exists with

and as value of tan.

If = 0, that is, if the wheel be cylindrical

* Sir John Herschel art, "Of Light," in the "Ency. Metrop."

ome individuals to detect certain colours, and which no amount of education, or acquaintance wi h colour, will entirely obliterate. Among sufferers from colour blindness, a wide range of relative degrees of inappreciation to colour exists. The first, and the most severe case, is fortunately rare. It occurs when the sufferer can discriminate between no two colours; when the entire spectrum such as we have described arising from the decomposition of light by a prism presents merely gradations of light and shade, of black and white. In Taylor's "Scientific Memoirs," 1846, several cases of this strongest form of what is properly called colour blindness are placed on record, some of which we shall quote in the sequel. Another form in which colour blindness (and here the term is inappropriately applied) manifests itself is constituted by an inability to discriminate between the nicer shades of the more composite colours, such as browns, greys, and neutral tints, and there exists a last class, with whom it is difficult to distinguish between the primary colours, red, blue, and yellow, or between these and secondary

colours.

When we speak of the existence of an eye, perfectly formed, that was totally incapable of detecting any difference in colour, and with whom all colours resolved themselves into intermediate shades between black and white, we do not mean to be understood that perfect achromatism has ever been met with. The subject has never been treated with that care by medical men to enable us to assert that any eye, perfectly formed, is under all circumstances insensitive to colour. The apparatus for polarising light has enabled the philosopher to produce the most brilliant and purest tints, and till an eye has been subjected to every test that can be suggested shall we be warranted in asserting that a case of absolute achromatism has been produced? "And even if a human eye were altogether unimpressible to colour, it seems exceedingly doubtful whether we should be able to discover that it was 80. We have it not in our power to subject an eye simply to the influence of colour. Every luminous ray is a bundle of colour-giving, heat-giving, and chemical or actinic rays, mingled in unequal proportion. Each colour ray, therefore, carries with it to the retina a diff rent number of heat rays and chemical rays. Thus, if for simplicity's sake, we assume only three colours to exist, red, blue, and yellow, then the red ray of the spectrum is, in reality, when tried by the thermometer, much hotter than the blue or yellow. The blue, which is the coldest and darkest of the three primary colours, greatly excels the red and yellow in the number of chemical rays which accompany it, whilst the yellow, which is totally destitute of such rays, and contains very few heat rays, must necessarily consist almost entirely of colour rays, and further excels red and blue in luminosity. The retina, accordingly, in so far as it is affected by heat, will be most influenced by the red ray, in so far as it is susceptible of chemical change, by the blue ray; and in so far as it is influenced by luminosity by the yellow ray, apart from the special impressions made upon it by each ray in virtue of the colour." When, therefore, we ask any one to gaze at a rainbow, and tell us what he sees in it, we ask him to report on a series of complex sensations, to the production of which the brightness, heat, colour, and chemical force present in the light by which he sees it, all do, or at least may, contribute.* It is not probable, therefore, that if we were to paint a rainbow in streaks of black and white paint mixed in due proportion, that we should be able to reproduce before a colour-blind person the exact effect that a rainbow presents to him, because there might be a certain chemical quantity wanting, which in the original rainbow produces an im pression on the eye of the colour-blind, though it is not such an impression as is produced on a normal eye by colour. For instance, Mr. Pole, whose eye is undoubtedly blind to red, and who distinctly asserts that "there is a hue of red which to me is colourless," could not form a red by merely mixing black and white in due proportions, but who to make red mixed one part of lampblack with five or six of chrome yellow, so as to darken it to the required tone. Carmine to his eye was produced by mixing nine parts of lampblack with one of chrome yellow.

Dr. G. Wilson on "Colour Blindness."

The second division that we have made among colour-blind people is marked by the inability to discriminate between the nicer shades of the more composite colours, and this class comprehends a far greater number of subjects than either the first or last. In this class the miscomprehension of colour is one of degree, and not of totality, and Dr. Wilson remarks that this defect seems to be rather the rule than the exception-at least among the male sex of this country. A defect of vision of this nature is probably to be overcome in some degree by education, and continual attention to colour. The inability to name a colour does not necessarily prove that the difference of the colour from any other is not marked on the retina. The scanty nomenclature employed by men generally in describing colour might lead one to suppose that they appreciated far fewer shades of colour than is actually the case. Even educated men are to be found who would call scarlet crimson, and magenta indiscriminately red, although they would be distinctly aware of difference between the colours arranged side by side. To judge, therefore, by the inability to name colours, we should conclude that colourblindness was much more common than it fortunately is. In testing, therefore, for this slight degree of non-discernment of colour, it is necessary to dispense with names of tints. Give to a person a number of squares of cloth, or skeins of wool, and request him to arrange them so that all of the same colour and shade may be placed together, in gradual succession from dark to light. We ourselves have submitted this test to many of our acquaintance,' and our experience is very similar to that of Dr. Wilson. Many will have no difficulty in arranging the full bright tints of the primary and secondary colours, but when the fainter tints come to be arranged, great hesitation will be often evidenced as to which bundle they ought to be placed in. The most frequent mistakes occur in blue and greon (of course the test is made in full daylight), while pink and pale blue are a stumbling block to many who are able to arrange all the other shades, and the pink and pale yellow are often interchanged. "In truth we are all by birth, colour-blind to some extent, and painters know how long it is before the most susceptible eye acquires its maximum sensibility to colour."

A peculiarity is often noticeable in the colour- amusing case of total colour blindness in the
blind, by the ease with which they can detect person of a house painter: "The explanation
objects assisted by the least possible light. A of his prosecuting a calling for which apparently
case is mentioned in Wartmann's paper on the he was so unfit is found in the fact that he was
Colour-Blind, of a woman who could detect no an excellent draughtsman, with a good eye for
difference of colour in the prismatic spectrum, form, and skilful in designing. He trusted to
and yet could read a book in a completely dark- his wife to keep him right in mixing and selecting
ened room. This may be accounted for by sup- his colours. On one occasion when she was out
posing that the perception of different coloured of the way, and workmen were scarce, he took a
tints to a normal eye induces a certain amount part himself in painting a public building, which
of fatigue to the retina, and renders it less sensi- he had been employed to put in order. He mixed
tive to faint light, from which the colour-blind the colours himself, and believed that he had
are free. Nor is it to be supposed that in cases produced a stone tint, with which he proceeded
where a normal eye perceives an object by the to colour the walls. After he had gone over
difference of colour from the objects surrounding some square yards, he was informed that he was
it, that a colour blind eye sees the object of a painting the building blue."
smaller size. For instance, in the spectrum
thrown upon a white screen, a normal eye is
sensible to its appearance by the variation of
colour, from the red extremity to the violet; to
the colour-blind the spectrum is equally long
and perfect in every particular except colour,
and the eye is made sensible of its existence by
the different degree of illumination that each
colour presents, and if the colour-blind person
had given to these different shades the terms
red, blue, green, &c., it would be impossible to
discover, from his description of what the spec-
trum presented, that he was a sufferer from
colour blindness. This fact is particularly shown
by the description of the spectrum by persons
affected with colour-blindness in the second
degree, that is, when two colours present pre-
cisely the same appearance, so that one colour
cannot be detected from the other. Dalton was
very particular on this point. The spectrum ap-
peared as long to him as it did to Sir David
Brewster, only Dalton saw one colour twice
over. An instance of this severe deprivation of
colour is described in the
sensitiveness to
"Philosophical Transactions" for 1777, in a
letter from a Mr. Huddart to Dr. Priestley. The
subject was a shoemaker, named Harris, living in
Cumberland. The following is the account he
gives of himself:-"That he had reason to be-
lieve other persons saw something in objects
which he could not see; that their language ap-
peared to mark qualities with precision and con-
fidence, which he could only guess at with hesi-
tation, and frequently with error. His first sus-
picion of this arose when he was about four years
old. Having, by accident, found in the street a
child's stocking, he carried it to a neighbouring
house to inquire for the owner; he observed that
the people called it a red stocking, though he
did not understand why people gave it that de-
nomination, as he himself thought it completely
described by being called a stocking. This cir-
cumstance, however, remained on his memory,
and, together with subsequent observations, led
him to a knowledge of his defect. He also ob-
served that when young, other children could dis-
cern cherries on a tree by some pretended dif-
ference of colour, though he could only dis-
tinguish them from the leaves by the differ-
ence of their size and shape.
I
believe he never could do more than guess the
name of any colour, yet he could distinguish
white from black, or black from any white or
bright colour. In general, colours of an equal
degree of brightness, however they might other-
wise differ, he confounded together." * There can
be little doubt but that this is one of the few reli-
able cases of a complete insensibility to colour,
and it is also related in the narrative of Mr. Hud-
dart, that this man had two brothers similarly
affected, and two other brothers and two sisters
whose vision presented no peculiarities. The fact
of this defect manifesting itself in more than one
member of a family is not uncommon; and there
is an instance of a gentleman who had seventeen
relations that suffered more or less from this
false vision, and often it appears that only the
male members of a family exhibit this pecu-
liarity. Indeed, the phenomena is much rarer
among females than among males, and our in-
genuity may be tortured to account for this fact.
It is however certain, from the facts that Dr.
Wilson collected, that when a female is marked
by this peculiarity she exerts herself to the utter-
most to hide it, which render statistics con-
cerning female colour-blindness very difficult to
accurately ascertain, and lead us to suppose that
the number is less than is really the fact.

Mr. Inglis, of Edinburgh, reports a rather

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For the general purposes of life, the slight error in the discernment of colour that this class exhibits is not likely to produce any very ill effect; not so, however, in the third and last division, in which the sufferers see no difference between the primary colours, red, blue, and yellow, or between these and secondary colours, or where the difference is so slightly marked that hesitation and confusion between these colours exist in the mind of the beholder. Dr. Wilson has devoted a large portion of his book to the consideration of circumstances in which colour is made to convey a certain amount of information to the mind, as in the case of railway signals and ships' lights. It is an unfortunate circumstance that, in the case of people who confound colours, red and green are the two colours that most often importance of these two colours in railway sigpresent a similar appearance to the eye, and the nalling is well known, and Dr. Wilson wisely doubts, considering the general prevalence of colour blindness, but that among the army of guards and signalmen of this country and the continent some cases may be found where the difference of red and green cannot be detected, and the danger of travelling is consequently increased. To those who are interested in the question we recommend his book, where they will find many amusing and instructive pages.

(To be continued.)

* Dr. Wilson, Op. Cit.

DRESSING MILLSTONES WITH THE

TE

DIAMOND OR "BORT."

. (Continued from page 128.)

HE first who appears to have thought that the action by which the glazier produces a rectilinear crack along the surface of glass with his diamond might be availed of for producing a series of fine grooves or cracks on the surface of a millstone, so as to form a suitable dress thereon, was D. M. Childs, of Rochester, United States, and a patent was obtained for his invention in this country by A. B. Childs, on 23rd August, 1861, No. 2107. In his provisional specification Mr. Childs says:

"The particulars of this invention relato to the application of the diamond or other mineral-cutting substance in the production of the small lines (or what is generally known as the cracking), in any required form upon the face of millstones. The diamond or other mineral cutting substance (of which one or more may be used) is to be drawn by the hand or by mechanical agency, so that the cutting edge or edges may cut into the face of the millstone, the fine line or cracks, instead of the ordinary metal mill-bill now used. Although I prefer the diamond to be drawn by the hand or by mechanical agency, I do not confine myself to that particular mode in the application of the diamond for the aforesaid purpose."

In his final specification, however, he makes no reference to "mechanical agency." Fig. 3 is a view of the instrument he uses, which is described in the following extracts from his specification, along with other interesting details:

:

"The tool is composed of one or more dia. monds inserted in a bit or handle, and when two or more diamonds are used, they are to be firmly set in a row at equal distances apart. The furrows or cracks are produced by running with adequate force the points or diamonds over the face of the stone where the lines are intended to be cut, and such operation may be conveniently performed by running the tool containing the diamond along the edge of a straight rule. Curved lines are made by operating the same diamond points by the side of a curved ruler. The width of the space separating the lines upon the grinding surface of the stone is regulated by holding the points more or less diagonally across the lines of motion.

"In order to show the precise nature of my improvements I will explain the ordinary modes of dressing millstones. In the ordinary mode, the pick, being brought down upon the face of the stone, produces the stellated fracture, and thereby weakens or disintegrates the stone as far as the fracture extends, and the edges of the crack which have been thus weakened by the blow from the pick soon crumble away, and the particles thus detached are thrown out and wear the face of the stone. These disadvantages are prevented by my improvements in dressing millstones.

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"The line cut by the diamond upon a glossy in a great measure owing to his using the common surface, which has never been detonated or disintegrated by a blow from a pick, is clear and distinct, having its edges sharp and fine. Millstones will be more perfect when dressed again according to my invention, as the diamond will cut below the bruises occasioned by the old mode of dressing with a pick.

"In the old mode of dressing with a pick the furrow is rough and nearly flat at the bottom, whereas furrows cut with the diamond are smooth, having the side upon which the grain rises a regular smooth inclined plane. There is no perceptible moisture generated in the operation of grinding with millstones dressed according to my process, and the sprouts are clean and dry, which I attribute to the fact that the grain is kept back or in towards the eye until well ground, and while the motion is less rapid, and consequently less 4 liable to heat. When the flour has reached the extreme of the breast circle it is rapidly thrown from the stone with few, if any, inequalities to retard its egress, and it will be found that much less power is required for grinding, when my mode of dressing is employed, to produce the same amount of a superior article of flour."

There cannot be a doubt but that millstones can be dressed by Mr. Childs' process in a practically satisfactory manner, and with much better results than by the steel pick; and it is to be regretted, as Mr. Childs was the first to use the diamond, that he received so little encouragement, and did not think it worth while to maintain his patent beyond its third year. Recent experience, however, makes i pretty pretty clear that his want of success was

translucent glazier's diamond, instead of bort,
which latter is not only less expensive, but in
every way better suited for the purpose, as we
shall shortly explain. It is true Mr. Childs in-
cluded "other mineral substances" in his patent,
but we understand his actual trials were confined
to the common diamond.

The second to use a diamond for millstone
dressing was J. Dickinson, of New York, who
invented a kind of parallel ruler for guiding the
hand in drawing the diamond along the surface
of the stone. His invention was patented in this
country in the name of J. A. Knight, on 16th
January, 1862, No. 118. The ruler was provided
with a ratchet-feed motion, by which the distances
apart of the lines were rendered regular; but the
ruler covered only a very small portion of the
stone at a time, and in no way tended to preserve
its truth or level.

In 1864, J. D. Jobin obtained a patent (No. 148) for a great variety of machine tools specially adapted for applying bort or carbon as cutters in working stone, marble, and other hard substances, and some of the combinations could have been used for producing the fine-groove dress upon millstones. It does not appear that they have as yet been used for that purpose, but there can be no doubt that this patent covers any use of bort as a substitute for steel covers. Indeed, the importance of this patent will necessitate our again referring to it.

To Samuel Golay, of Paris, undoubtedly belongs the credit of first introducing a practically successful method of dressing millstones otherwise

than by the old handbill, and his merit is in no way diminished by the fact that since his plan was made known, others of at least equal efficiency, and possessing some advantages over his, have made their appearance. Golay's apparatus was shown in the Paris Exhibition, but attracted no attention. It was patented in this country in the name of G. Davies, on 30th April, 1867 (No. 1245). The British patent was purchased at the commencement of 1868 for, we believe, something less than £4000. The invention was practically tested, and it was decided to charge millers a royalty of £50 per pair of stones for the right to use it, several millers valuing it so much as to be quite willing to pay that sum. The original purchasers of the patent were fortunate in finding numerous parties willing to take off their hands the trouble of dealing individually with the mul titude of millers scattered over the country, and by the middle of the same year they had sold licenses for various districts for prices amounting altogether to close on the amazing sum of £200,000.

Our readers will be curious to know the details of a machine occasioning such extensive transac tions in so short a time, and we need no excuse in transferring from the specification to our columns the following full description

:

"It is well kuown that for several years the employment as a tool of hard stone, and especially of the diamond, has been adopted in various trades. Different applications have been made of these stones in working stones less hard, such as granite and others, and it is by a new application of this principle that the inventor has arrived at

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