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A drum is fixed upon the axis of the pulley at the edge of
the table; over this drum is stretched a sheet of paper, and,
during the motion of the pulley, a pencil whose point is
pressed against the surface of paper is caused to move with
uniform velocity parallel to the axis of the drum.

As the pencil has thus two simultaneous motions,
in directions at right angles to each other, a curve
must be the result, and if this curve be a parabola, it
is easily shown that the acceleration of a point on the
drum, and therefore of the sliding body (since the cord
moves with the same velocity as a point on the drum), must
be constant, and consequently that friction is inde pendent of
the velocity; for if the motion of the sliding body be uniformly
accelerated it must be acted upon by a
A
C
constant force, and therefore the friction
cannot vary with the velocity.

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B

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was

In Fig. 11, let A B E be a portion of the parabolic are described (for in the experiments a parabolic arc clearly obtained), whose axis, A D, is at E right angles to the axis of the pulley, let B be the position of the pencil's point after the interval of time from the commencement of the motion, draw B C perpendicular to A C, a tangent at

2

AC

BC=

P

but if be the uniform motion given to
12 2

P

He commenced by giving some farther particulars relative to! the artificial modes of producing ice. The materials suitable for abstracting heat from water in sufficient quantities to be aralabe for reducing temperature were, liquid ammonia, airabal, and ether. The substance hitherto used for prodering cold had been almost entirely ether vapour, with the exception of the expansion of air, To produce a lb. of ice, we required to take out of water at a temperature of 60° a quantity of heat represented by 142 heat units, and to cool the water from the temperature of 60° to that of 32°. Speaking of this in larger quantities, the lecturer said that 2848)b. of ethez required to be vaporised in order to convert one ton of water at 60° into ice at 320. Although there was a great difference between the quantity of those materials which were requisite to produce this change, experience went to show that the solution of ammonia was the most efficient material to be used for absorbing heat from water to convert it into ice. Still, ether had the advantage of being susceptible to vaporisation at low temperatures. Neither water nor alcohol would vaporise at a low temperature with anything Eke that degree of rapidity which would suffice for artificial cooling. The doctor then described the way in which ether was used. It' might appear remarkable that fuel should be used for producing cold, but the reason was, that the rate of evaporisation that corresponded to the tension of ether would be too large to produce any appreciable cooling, or sufficient cooling of water to produce ice. Therefore, the A, then, by the well known property of the parabola, if p eraporisation of ether had to be facilitated by mechanical be the latus rectum means. With the aid of a diagram the lecturer explained the whole of this process, and then spoke of the ether apparatus. A machine capable of producing five tons of ice in the space of 24 hours consumed a quantity of fuel which was in the proportion of llb. of fuel to 3lb. of ice produced. The tension of vapour varied according to temperature, and that the pencil, A Ctr, therefore A C2 and BC = —— had an important influence on the efficacy and work of this material in the production of ice. That, in brief, explained the way that fuel had to be consumed in making ice by means of ether. Ammonia, at an ordinary temperature, was a gaseous substance, requiring a pressure of about 150lb. on the square inch to reduce and maintain it in a liquid form. If we used ammonia to produce ice, it must be at the expenditure of a considerable amount of power and of fuel. When we remembered that in the steam engine there was not, generally speaking, more than one-tenth of the heat produced by coal burnt which became affected by mechanical force, it must be evident that this mode of working ammonia must be very costly; and so it had been found to be. But, on the other hand, there was found to be a faculty characteristic of ammonia which rendered it possible to do away with this application of mechanical power. That character was the faculty of ammonia for being absorbed into water, and this characteristic had been taken advantage of in working the ammonia machine, as he showed by reference to two diagrams of ammonia machines used in the production of cold. In both a strong solution of ammonia was separated, and used over again; but the special advantage of one of them was that liquid ammonia was obtained much more free from water than in the other. The expansion of air had also been applied to this purpose; but this was so expensive a way of producing refrigeration, as almost to place its use out of the question. Artificial refrigerators were now in use, and he had only lately been informed that in the breweries of London there were cooling machines working which were capable of cooling as much as nine hundred barrels an hour to the extent of 10 degrees, which was equivalent to the cooling of 324,000 gallons an hour, and that quantity cooled 10 degrees was equivalent to the melting of 10 tons of ice an hour. At this point Dr. Paul entered upon that part of his subject which should have commenced his lecture. He began by showing the uses of fuel for the production of high temperatures, and observed that the temperature produced by the combustion of fuel depended much more upon the way in which the heat generated was disposed of in the production of combustion than it did in the actual amount of heat.

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As friction con

include every circumstance of the case.
sidered as a resistance constantly retarding the motion of
bodies has now been introduced, I shall here give the solu-
tion of an useful problem respecting the motion of a body
along a series of inclined planes, and it may here be re-
marked that all the questions which have been given on the
friction of sliding bodies apply generally to that of rolling
bodies, for it is clear that the resistances to the motion of
carriages, as on roads and railways, due to friction are made
up of rolling and axle friction, which together may be taken
to be some definite proportion of the weight of the carriages.
The resistance of friction on roads and railways shall however
receive a separate account hereafter.

The following is the problem :

A body having descended one incline of given length and inclination, is stopped on its descent or ascent) on another also of given length and inclination. To find the friction which stops the body.

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In Fig. 12, let the body start from and, having descended a b, let it come to rest at d, a point on the incline be. Let B and B' be the inclinations of ab and be to the horizon. Now if W be the weight of the body, W (sin. but is constant, hence B C bears a constant ration to 2, or Bμ cos. B) as has been before explained, is the force which urges the body down the plane, or, dividing by M, the the spaces traversed by a point parallel to the axis A D of mass of the body, we have, since W = Mg, g (sin B-μ cos. B) the parabola vary as the squares of the times of traversing for the dynamical acceleration of the downward motion, therethem; but a point under the influence of an uniform accele-fore, if v be the velocity of the body on arriving at 6, and if s be ration traverses spaces proportional to the squares of the the length of a 6, we have r2 = 2g (sin. B-μ cos. B) s, by the times, therefore a point which describes a parabola must be relation between velocity and space described. Now if we under the influence of an uniform acceleration. suppose the body to pass from ab to be without loss of velolocity, we have its velocity on starting from bequal to v, and by the nature of the question, this velocity is destroyed by friction when the body arrives at d, therefore the friction, or μ W cos. B', is greater than W sin. B', or the component of the weight along the plane be. The dynamical retardation of the motion along be is therefore g (μ cos. B'-sin. 3'), and the relation between the final velocity (in this case o) and the space described when the body has an initial velocity, we must have o = v2 - 2g (μ cos. B'-sin. B') sur

Let f be the dynamical measure of this acceleration in feet per second, and we have C B = f 2, by the relation therefore ƒ = between space and time, also C B =

-

12 02

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In experiments such as the above, where acceleration takes
place, it is clear that the descending weight exceeds the
friction by a certain quantity; we must therefore find an ex-
pression for u in this case in terms of known quantities. Let Q
be the sliding body drawn along by a descending weight P.
then we have the weight P+Q set in motion by the force P
HQ, since the moving force is P lessened by the friction
u Q, and if f be the acceleration, as found above, we must
have by the laws of motion, P + Q : P − μ Q : : g : ƒ †,
where g is the dynamical force of gravity expressed in feet per
second.
P(9-1)-qr
Qg

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r2 = 2g (μ cos. ß' — sin. B') s'. Equating this value of to that found above, and dividing across by 2g, we have còs. B' ssin. B-sμ cos. ẞ = s' sin. B' Draw now the horizontal lines b c and d h, and put a c therefore sin. B =2 Example 8-A mass of cast iron, weighing 1001b., is = ', c b = r, and hd = x'; = I, 5 cos. B' drawn along a horizontal plane of cast-iron by means of a 5 μ cos. B μ cord which is parallel to the plane, and to the end of which =, therefore με = μ a weight of 2016. is attached. Determine the coefficient of friction, if the acceleration, found as above described, be 1ft. per second, 20 × (321) · 100 × 11

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This was especially important in the use of fuel in such operations as the Juanufacture of iron. The specific heat of almost all substances increased as the temperature increased. In the case of iron it was more than double at that high temperature required to be maintained in the puddling furnace. The consumption of fuel in puddling iron was at the rate of a ton of fuel for every ton of iron produced, or something like 18 times as much as the quantity of fuel represented in the actual work done. By this he meant the heating of the pig iron up to the temperature necessary for producing the change required in puddling and for melting iron. Fuel, under existing circumstances, was indispensable. Speaking of gas, the lecturer said that the specific heat requisite to raise the temperature of 131b. of gas 1 degree was about three heat onita. In the furnace three-eighths of the heat was used, and five-eighths passed off in waste; and this proportion applied to glass-making and to all operations necessary to be conducted at a high temperature. The higher the Substituting this value for ƒ in the above value for μ we have The reader may verify the above result in the case of three temperature produced, the greater the amount of free heat there was available for the work to be done, and the greater was the economy of fuel. At high temperature there was a rapid waste of heat by radiation and conduction, and by escape in various ways. The temperature regulated the amount of work done. Dr. Paul next alluded to the use of fuel for producing high temperature for the production of iron in what was called the smelting furnace, the conditions of which prevailed in the hot air blast furnace. By means of a diagram he showed the difference between ordinary combustion and that taking place in this furnace. In the smelting furnace, carbonic acid was converted into carbonic oxide, which was combustible, and which furnished heat and effected a saving of fuel. In many cases the consumption of fuel ran up as much as three times the weight of the iron produced; and this large expenditure of fuel was attributable to the e causes which operated in the case of the puddling fur

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From this last formula it will be seen that we can deter

mine the coefficient of friction by observing the time the
weight takes to fall any given space, without knowing the
value of the acceleration.

In the above examples it should be observed that the fol-
lowing are not taken into account. The weight and rigidity
of the cord, the inertia of the pulley and the friction of its
axis. They are therefore given to indicate merely the manner
of experimenting, as the formulæ actually employed should

*Or, to speak more correctly, the pencil bas one motion, and the paper has another; but the result is the same as if the pencil had the combined motion of the two relatively to a fixed point on the paper.

This statement is merely an instance of the law of motion that the velocities produced in the same body by different statical forces, acting for the same time, are proportional to those forces.

(To be continued.)

THE ACTION OF MAGNETISM UPON LIGHT. FATHER SECCHI, the great Italian physicist, has recently laid before the French Academy of Sciences an account of some experiments he has been making conjointly with Professor Provenzali, upon the modifications produced by magnetism upon the light emitted by the rarefied gases. In theire xperiments they employed a large Bunsen's battery, capable of giving sparks eight centimetres in length from the induction coil The gases were confined in Geissler's tubes.

The results of their observations have been classed under two heads:

1st. Whenever a tube of wide bore is introduced between or brought into the neighbourhood of the poles of the electromagnet, it is found that the diffused or stratified light which fills the tube when a current is passed through becomes repelled by the poles, and is condensed on the opposite side of the tube, where it appears as a bright streak instead of a luminous glow. Indeed, the effect is as though the gas itself were really displaced, and accumulated in the more distant part of the tube. Father Secchi considers that the appearance presents a great similarity to the movements of the streamers in the Aurora Borealis

2nd. The condensed gas gives a well-defined and brilliant spectrum, and when the current is of sufficient intensity and the gas is one, such as chlorine or nitrogen, which gives a double spectrum, both spectra may be observed, the one in that part of the tube opposite to the magnetic poles being more intense than that in the main body of the tube. It is considered as proved that the double spectrum is due to a difference of temperature, and not to impurity of the gas, as was supposed by M. Dubrumfaut. A very striking result was presented by the hydrogen tube. In this the light brought under magnetic influence became of a bright yellow colour, while the other part was of a magnificent roseate tint, the blending of the two colours strongly resembling in their shades the solar protuberances (red flames) of the eclipse of 1860. The experimentalists think this effect partially due to the decomposition of the glass under the great heat of the current. Father Secchi suggests that a simple solution of the phenomena observed may be summed up thus. Magnetism acts as though it contracted the bore of the tubes, and by producing an elevated temperature causes the gas to give a spectru m similar to that which would be given in a tube of small capacity, and so it may be ascribed to diamagnetism. In conclution, he says it is impossible to observe these phenomena without comparing them with the magnificent phenomena of the solar chromosphere, and thinks that by similar experiments it may be possible to carry the analogy farther. G. M. W.

[We are indebted for the above communication to G. M. Whipple, Esq. of the Kew Observatory. In regard to the first class mentioned, we showed precisely similar results in 1856 to Faraday. We produced the vacuum in an ordinary barometer tube, 36in. long, in the top of which a platinum wire was soldered, the mercury serving as the other conductor from a Rhumkorf. Faraday exhibited the experi ment at a subsequent Friday evening's meeting at the Royal Institution, while lecturing on the induction coil-Ed. E. T and R. R.]-Electric Telegraph and Railway Review.

ASTRONOMICAL NOTES FOR APRIL.
BY A FELLOW OF THE ROYAL ASTRONOMI CAL
SOCIETY.

Venus is a morning Star during the entire month'
Southing at 9b. 31m. a.m. on the 1st, and at 9b. 5m, a.m.
on the 30th. She is still a fine telescopic object, albeit
the difference in the thickness of her crescent is very
marked when contrasted with the extraordinary
tenuity which it exhibited in February. Mars is still
too close to the Sun to be visible. Jupiter is now
visibly creeping towards the West. It is on the
Meridian at 2h. 38m. on the 1st, and at 1h. 10m. in the
afternoon on the 30th. We shall soon be losing him
as a conspicuous celestial object, for the season. He
remains in Taurus during the entire month. Saturn is
a morning Star until the 19th, after which he rises
before midnight: he is, however, close to the horizon,
and wretchedly situated for observation. He is on
the confines of Sagittarius. Uranus may still be
observed before midnight; his position is Gemini
has not sensibly altered from that laid down in our
little, map on p. 470. Neptune is now invisible, in fact
he is actually in conjunction with the Sun about 8
o'clock in the morning of the 9th.

The Phenomena exhibited Jupiter's Satellites are very much fewer, the Planet's approach to the Sun interfering materially with their visibility. On the night of April 1st there will be a transit of the 1st Satellite. It will enter on to Jupiter's disc at 9h. 7m. On the 2nd the 1st Satellite will re-appear from Eclipse at 9h. 29m. 328, but Jupiter will be very low down. The shadow of the same Satellite will pass off the Planet's limb at 6h. 41m. on the next evening: the Sun, however, will only just have set at the time. Strong twilight may also prevent the Emersion of the 3rd Satellite from Eclipse at 7h. 19m, 598, on the evening of the 4th from being observed. On the 5th the Ingress of the Shadow of the 2nd Satiliite will take place at 7h. 30m. The Satellite itself will pass off at the opposite THE Right Ascension of the Sun on the 1st of April limb at Sh. 20m., and its shadow may probably be seen will be 0h. 42m. 31s., and his North Declination 4° 34' to follow it at 9h. 55m., but Jupiter will then be on the Point of setting. On the 9th, Satellite 1 will be occulted 30". He will, therefore, be close to Piscium; and at Sh 30m. On the 10th the same Satellite will leave reference to our maps on p. 64, will show what constellations will in consequence be lost in his rays, and Jupiter's disc at 7h. 52m., to be followed by its shadow therefore invisible. The Equation of time to be added at 8h. 36m. On the 11th the 3rd Satellite will re-appear to the instant indicated by a sundial, will on the 1st from occultation at 8h. 42m., only to be Eclipsed by day of the month be 3m. 56s. It will diminish until Jupiter's Shadow at 9h. 29m. 268. This is only some the 15th, when there will be no Equation at all; the 18 minutes, though, before he will set. The 2nd Satellite clock and dial being coincident. After this the Sun will enter on to the Planet's limb at 8h. 42m. on the will south before mean noon, or the Equation will be- night of the 12th. On the Evening of the 17th there come subtractive, and on the 30th, 2m. 55s. must be will be a transit of the 1st Satellite. It will pass on to taken from the instant of apparent noon to obtain the Jupiter's disc at 7h.40m., and its shadow will come after time, which a properly regulated clock ought to show. it at 8h. 18m. The first Satellite may also be seen in the The Sun is now longer above the horizon, in these lati- twilight to re-appear from Eclipse at 7h. 49m. 16s. on tudes, than he is beneath it; the length of the day at the evening of the 18th. Five minutes before Jupiter sets the beginning of April being 12h. 53m., and on the last-viz., at 9h. 15m. 338. on the night of the 21st, the 2nd day of the month 14h. 42m. Satellite will re-appear from Eclipse. The 2nd SatelThe Moon enters her First quarter at 25 and a half lite will be occulted at 8h. 34m. on the 28th, or on the minutes past 4 a.m. on the 9th; is Full at 10k. 26m. on succeeding Evening, the 29th, the ingress of the shadow the night of the 15th, when, as she will be in Perigee, of the 3rd will take place at 7h. 26m.: the egress of or at her nearest to the Earth, about half an hour the Satellite itself occurring at 7h. 56m. We should afterwards, a high tide may be looked for: She will perhaps add, that as many of the phenomena, which we enter her Last Quarter at 4h. 25m. on the afternoon of have included in the foregoing list will take place in the 22nd and be New at 6h. 37m. on that of the 30th. strong twilight, or when the planet is almost close to The Moon will be in conjunction with Jupiter at 49 the horizon, it will require a good telescope to observe minutes past 10 on the morning of the 4th: in conjunc-them: even assuming, what is problematical, that such tion with Uranus at 2h. 38m. in the early morning an instrument will render all of them visible. of the ninth in conjunction with Saturn at 3h, 40m. 10 There would seem to be some reason to expect Shoot a.m. on the 20th: in conjunction with Venus at 9b. 53m.ing Stars in April, during two intervals; the first beam. on the 26th: and finally with Mars at 4h. 10m. on the afternoon of the 9th. Practically the first and two last of these conjunctions will be invisible. During this month Five Fixed Stars, and the Planet Saturn will be occulted. At 1h. 47m. in the early morning of the 9th, 56 Geminorum will disappear at the Moon's dark limb; and re-appear at her bright limb at 1h. 59m. At 2h. 15m. a.m. on the 12th, 34 Leonis will disappear at the dark limb; to re-appear again at the bright one at 4 minutes past 3. At 48 minutes after midnight on the 13th, b Virginis will be occulted by the Moon's dark limb, and emerge from her bright limb at 2 minutes past 1. The bright limb of the moon will occult Libræ at 12h. 16m. on the night of the 17th, and at 6 minutes past 1 it will re-appear from the dark one. The occultation of Saturn will take place during the early morning of the 20th. The COMPOSITIONS FOR THE BOTTOMS OF planet will disappear at the bright limb at 2h. 55m., and VESSELS.-Mr. Gibbs, of Milton-street, City, re-appear at the dark one at 4h. 5m. Lastly, Sagittarii proposes to coat the bottoms of iron vessels, to will be occulted by the Moon before she rises after mid-preserve them from fouling by the employment of a night on the 20th; but, after she has risen, will re-appear and resin, to which is added a saturated solution of mixture of tallow, or other greasy or fatty matters from her dark limb at 6 minutes past 1. The Moon's sulphur (in caustic or carbonate alkali or lime), in age on the 1st, at noon, is 04 days; She is 14 days which copper has also been previously dissolved. The old at noon on the 2nd, and so on. At 9 o'clock compositions are prepared by the agency of heat or in the evening of the 9th, Libration will bring otherwise, and they are to be applied hot to the ships or vessels by means of a brush. The composition is a portion of the S.E. part of her disc into view; while prepared by taking sulphur, such as is known in at midnight on the 21st an additional portion of the sur- commerce under that term in the proportion of 171b. face in the S.W. quadrant will become visible from the to 52lb. of potash leys of 35deg. strength, and 1lb. of same cause. These details, as has been before ex- pieces or plates of copper, which are all mixed together in a vessel heated by steam or otherwise, the plained, are given to facilitate the observation of the heat being kept up until the sulphur and copper are thoroughly dissolved. In another vessel, heated in like manner as aforesaid, is mixed tallow in the proportion of 74cwt. to 1hcwt. of resin or resin oil, and the heat is to be kept up until the mixture is well liquefied. The two mixtures thus separately prepared are to be mixed together and thoroughly amalgamated by agitation in the heating vessels.

various features of the Lunar surface.

Mercury is practically invisible during the first twothirds of April; but becomes an evening Star, and may be looked for towards the end of it. During the las two or three days, he may be seen glittering close to the horizon, to the North of West after Sunset.

tween the 4th and the 11th: the second between the
17th and 25th of the month. Watch should, therefore,
be kept about these dates.

same person.

CONSUMPTION OF FROGS IN FRANCE.-The Echo du Luxembourg states that the exportation of frogs from that country to France has increased considerably of late. Upwards of 200,000 were sent in three weeks by one dealer, and on one day 30,000 were sent by the They are sent principally to Rheims, Nancy, and Paris. A thousand frogs fetch 13 francs (10s. 5d.), and weigh 50 kils., or about one cwt. Νο duty is charged by the French Custom-house on frogs. At Rheims, 25 pairs of frogs' legs can be bought for 60 centimes. The autumn and spring are the best times of the year for frogs.

LETTERS TO THE EDITOR.

[We do not hold ourselves responsible for the opinions of our correspondents. The EDITOR respectfully requests that all communications should be drawn up as briefly as possible.]

All communications should be addressed to the EDITOR of the ENGLISH MECHANIC, 31, Tavistockstreet, Covent Garden, W.C.

All eheques and Post Office Orders to be made payable to J. PASSMORE EDWARDS.

I would have every one write what he knows, and as much as he knows, but no more; and that not in

this only, but in all other subjects: For such a person may have some particular knowledge and experience of the nature of such a person or such a fountain, that, as to other things, knows no more than what everybody does, and yet to keep a slutter with this little pittance of his, will undertake to write the whole body of physicks: a vice from whence great inconveniences derive their original. - Montaigne's Essays.

THE TELESCOPE, &c.

SIR,-"J.T." p. 640 says: "it requires at least a 8
(meaning. I assume a 6in) refracter to see the Satellites
7in. in England which will show the two brighter
of Uranus Will he kindly tell me where there is a
ones; or an Sin. that will exhibit all four of these
Moons? The possessors of such instruments should,
if they be readers of THE ENGLISH MECHANIC, in the
interests of science publish the names and addresses of
their makers in your columns.

form of Equatoreal with which
In answer to Jupiter," (2039), p. 642, the cheapest
am acquainted is
the invention of a Mr. Vallance, and is described with
engravings, at p. 394 of your second volume, (No. 52).
8 of THE ENGLISH MECHANIC, (No. 195); and thi
A much more elaborate one is figured on p. 284, Vol.
latter possesses the advantage of adjustability to
different latitudes; or is of the form known as the
your engraving, though, should be carefully eschewed
"universal equatoreal." The tripod stand shown in
as vibration, greater or less, will take place with the
best possible wooden legged support. A brick or
stone pier is the only legitimate one. Horne and
don, make a cheap and efficient mounting on this prin-
Thornthwaite, the opticians, of Newgate-street, Lon-.
ciple. If, however, "Jupiter" seeks excellence and
not merely low cost, I have no hesitation in saying
that the most perfect form of Equatoreal extant is that
of Cooke and Sons, of York. A Dallmeyer object glass
on a Cooke mounting would be the very luxury of
observational astronomy.

I am unaware that I ever promised to do more than examine the region round about Mizar and Alcor." and difficult task of gauging the magnitude of every I am very certain that I never set myself the dreary point of light I might pick up. However, as a matter of fact, the weather has been so wretchedly, bad for the last month or two, as quite to put a stop to mere night at once moonless and cloudless, and state in star gazing. If your correspondent will ensure me a your columns for what date he has secured it, I will devote that night to his interests.

Apropos of the 3in. telescope which showed Jupiter's Satellites before sunset on the 26th of last February, sharp, as must also your correspondent's eye; and I may observe that its definition must be remarkably further, that the air must have b en exceptionally clear on the occasion to which he refeis. The instrument of which he speaks could show Polaris (a 2nd magnitolerably free from vapour, but then, as he knows, the tune star) at 2 p.m. on a sunny day, were the air Pole Star is in the least illuminated part of the sky. I question extremely if he could pick up a 3rd magnitude star in any portion of the Heavens under the circumstances specified.

The "Irish Mechanic" (208), p. 660, will find that 2in. is the minimum aperture of a telescope with which he can hope to do any good whatever in astronomical observation; and the range of this is very limited indeed.

"A Poor Lad" (2140), p. 21, should, by all means, expend his £2 in the purchase of a 5in. speculum. Assuming it to be properly parabolised, it would be equal in separating power to an achromatic of the same aperture, i.e., would divide double stars 0-87 apart; while, according to Browning's formula, its light-grasping power would be equal to that of an object glass of about 42in. in diameter. A 2in. object glass could not possibly divorce anything closer than a pair of stars 2-5 distant from each other, and a standard 11th magnitude star would be its minimum visible, while with a 5in. speculum your correspondent would see those of the 12 3 magnitude.

"H. F." (2199), p. 22, should read Vols, VIII. and IX. of the ENGLISH MECHANIC.

the eye tube of any telescope sufficiently beyond the "Ethardo" (2221), same page, has only to push in point of adjustment for ordinary sight, to suit his

own.

If "Neptune " (2224), has been a subscriber to the ENGLISH MECHANIC for any length of time, he must know that I have, over and over again, declined to solve Equations, or, in fact, to execute any merely mechanical computation, or "do sums" in any shape or way. But, even if I made an exception in his favour, I could not do it with the data which he gives. There is not a single syllable about the refrac tive or dispersive indices of the crown and flint glasses that he proposes to use. The sole item of information is confined to the assertion that he means to use a crown lens of 6ft. 10in. focal length. Now, if he has got hold of two of Chauce's discs of glass, of which the dispersive powers are, probably, somewhere about 055 for the flint, and 039 for the crown, I do not see

how he can possibly achromatise such crown (assum-
ing its focus to be oft. 10in.) without combining it
with a flint one of about 9ft. sin. focal length; which
would cause the joint focus to approach to some 23ft,
er äft. longer than he seeks to obtain. This is the
result of the very roughest conceivable calculation on
the margin of my writing paper, and has no preten-
sion to be considered rigidly accurate through.
If Neptune" will get "Coddington's Opties."
can use a table of logarithms, and will, first and fore-
most, determine the refractive and dispersive powers
of the materials he proposes to work with, he ought
to have no very hard task in getting out the curves for
bimself. It is not so much a difficult calculation, as a

long and very dreary one.
AFELLOW OF THE ROYAL ASTRONOMICAL SOCIETY.

ordered to make a map of London from them; and the subject, from some good treatise, such as "Her
as his questions at presen
whether he would be contented with them on the schel on the Telescope:
ground that they might possibly be useful in so re-evidently show he needs more information than space
will permit in the pages of the MECHANIC; for al
mote a contingency?
There is a popular superstition that the materials though four words would suffice to answer his ques
for the use of the computers of the "Nautical Almanac" tions, I fear the information would not be of muc
W. PURKISS.
are supplied by the Royal Observatory at Greenwich. service to him.
Is the theory of the Jovian System beneath the notice
of that August Establishment; or do the Heads of it
THE SUPPO SED PLANET, VULCAN.
consider that as the servants say) "it is not their
STB-Some of your readers may be interested in
place" to help to remove, what I must persist in
considering to be, a blot from our National Ephemeris? learning that another systematic search for the sus
I fear that we have here only another illustration pected intra-mercurial planet, Vulcan, commence
of the truth of the old preverb, that," What is every-on March 20. There will be about twenty-five gentle
body's business, is nobody's business."
men engaged in the affair, many of whom are in the pos
session of very powerful telescopes. The observation
will extend over the period from March 20 to April 10.
During this time the solar discs will be continually
under observation when visible. The following are the
names of observers, together with a description of the
telescopes employed and the times of observation:-

I suspect, however, that, after all, it is merely a question of money. Tables are somewhat costly, and until public opinion is brought to bear very much more directly upon the heads of the State than it is now, there will always be great diffculty in getting pecuniary aid from the Exchequer for anything, the use of which does not appeal immediately to the official mind. As far as the immediate object of this discussion is concerned, though, the abolition of a single embassy to one of the beggarly little German Courts would pay for the tables demanded at once. The first year's salaries of the well-bred hangers on who idle there at the Public Cost, would more than suffice to secure us trustworthy data to eliminate a glaring disfigurement from what is, otherwise, a perfect marvel of accuracy.

DEPRECATORY AND EXPLANATORY. B-Boswell records of Doctor Johnson that "A Tady once asked him how he came to define Pastern the kuce of a horse? Instead of making an elaborate defence, as she expected, he at once answered Ignorance, Madam, pure ignorance." May I be allowed to vindicate myself in the same way with reference to the charge brought against me on p. 655 by Omicron" of joking at his expense? D'Arrest's Comet I did know; the name of the computer of its Ephemeris I did not know. I was thankful to "Omicron " "for the offer of what I know would be useful to a considerable number of observers, and IÀ FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY. took (what I believed to be his spelling on trust. Hinc ille lachryma.

If it will afford Mr. Proctor the very smallest satisfaction I will confess that I think it extremely likely that I was wrong in my conjecture as to the possible mode of action of an object glass of large aperture in rendering solar detail visible; but at the same time I must assure him that it was not to escape making this admission that I terminated the discussion, as far as I was concerned. To render myself amenable to the charge of ceasing to argue when I find argument going against me, I ought, as it seems to me, to continue to argue when I am on the winning side; wherea it is notorious to every one of my brother readers of the ENGLISH MECHANIC, that I have eschewed discussion ab initio, on every moot point whatever. I have in the outset, said my say, and if ever a second letter from me has appeared on the same subject, it has been merely explanatory, or to remove some misconception of my meaning. I suppose that there are very few men of science who would value, or defer to, Mr. Proctor's opinion more than I should; but even such deference and appreciation would not prompt me to crumple up a polemical pewter pot merely that I might figure among Mr. Proctor's "strong men." A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY.

LIGHT.

"

THE BELTS OF JUPITER, &c.

SIR, Many thanks to Mr. Proctor and "F.R.A.S.." for their answers to my question on the above subject, and particularly to Mr. Denning, whose concise and appropriate letter (page 655), is all that could be desired.

regret that I cannot say so much for Mr. Grover's letter (on the same page), and had he given the same attention to my remarks that he supposes I have failed to give to Mr. Browning's remarks in the Student. Mr. G.'s letter might have been more to the point; as it is, he makes the question (if I understand him rightly) a question of chromaticity, instead of one of relative luminosity. In my letter I purposely avoided the word colour, to prevent misconception, but as Mr. Grover's letter is almost exclusively on colour, it fails, so far, to touch the question. Lest, however, his remarks should be considered by some of your readers to be a satisfactory answer to the question in hand, I cannot allow them to pass unnoticed. In the first place, there can be no doubt that large apertures, combined with high powers, are necessary to bring out delicate gradations of colour or chromaticity; but the same rule, I imagine, does not apply to the broad masses of light and shade. As an instance of this, I may mention that when using a 3in refractor, by Wray, simultaneously with my 9in. reflector, the dark belts have appeared much darker with 3in. than with

Sir, The following table will probably meet the 9in. aperture, notwithstanding the advantage which requirements of Mr. A. J. Smart (2004) p. 642.

Colours.

Length of
Undula-
'tious in
parts of an
inch.

Number

of Un- Number of Undudulations lations per second. in an inch

Extreme Red

Red

Orange

0-0000266 37640
0-0000256 39180
0-00-0240 41610

Yellow

Green

Blue ..

Indigo

Violet

0.0000227 44000
0-0000211 47460

0.0000196 51110
0-0000185 54070
0.0000174 57490

Extr. Violet 0 0000167 59750

the reflector possessed over the other in point of definition, and a precisely similar effect was produced by diminishing the aperture of the mirror. Just in probelts, so it rendered the dark belts still darker, and portion as this diluted the brilliancy of the bright thus the same relative contrast between the light and dark beits remained unchanged, whatever aperture was used; and more than this, when the air has been unsteady, I have always found the belts more 458,000000, 000000 positive and conspicuous with a small, than with a 477,000000,000000 large aperture. I cannot quite agree with Mr. 506,000000,000000 Grover's opinion that no pigments or materials with 585.000000,000000 which we are acquainted can be made to accurately 577,000000,000000 represent the differences which do exist; and yet he 622,000000, 000000 has just admitted that "Mr. Browning's drawing is 658,000000 000000 too vivid in colour." Perhaps Mr. Grover can throw 699.000000 000000 a little more light upon this apparent paradox. In the 727,000000 000000 meanwhile, my humble opinion is, that at the period at With reference to the request of "T.A." on p. 658, I appeared even more vivid than the engraving in the which Mr. Browning's drawing was taken, Jupiter must regret my inability to make even a guess worth Student, and I cannot, for my own part, see the slightest listening to, as to the reason why the more refrangible difficulty in finding pigments that would have exactly rays of the spectrum are absent at times from the expressed this brilliancy, without the heaviness and light of the sky. I have myself noticed when photo-opacity which now exist in the engraving, and which graphing, that the time of exposure which sufficed on fault, I cannot but think, is more the result of accione day was wholly insufficient on another; but, inasmuch as this deficiency of actinism seems to follow the final paragraph in Mr. Grover's letter will not bear dent than of any error in the original drawing. Again, no law, I was always content to recognise it as a fact, criticism, for if delicate gradation of shade require to without attempting to account for it. A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY. the lights, how is it that artists are able to give in a be so much exaggerated to give sufficient intensity to painting the relative degrees of light, shade, and perspective to the clouds of a summer sky, and yet preserve throughout such a glowing luminosity as to far exceed the brightest tints of the landscape? Unfortunately for the science of astronomy, it would seem that but few skilful draughtsmen enlist their talents in her service, and so difficulties are made of things which ought to be comparatively easy; if, however, we are yet to gain any further knowledge of the physical constitution of these remote worlds, it can only be by scrupulous accuracy in observation, delineation, and description, and anything emanating from good an authority as Mr. Browning certainly deserves criticism, and that is far more than can be said of the miserable attempts at planetary drawing which too often find their way into public journals and treatises on astronomy.

80

THE “NAUTICAL ALMANAC" AND "FRA.S."
SIR,-I freely admit, in limine, the correctness of
the assertion of" W. E. P.," p. 14, that, "It is the duty
of computers attached to that (the 'Nautical Almanac
establishment to use, and not to form tables." The
Superintendent of the "Nautical Almanac, "as such, is
by no means bound to make his own. All he has to do
is to see that the computations executed by the aid
of those supplied to him are correct; and that Mr.
Hind does this, and does it with the very utmost
efficiency, no one is readier to allow than I am.
The question, however, is a little wider than this,
Surely your correspondent does not mean to contend
shat a mass of observations of Jupiter's Satellites
has not accumulated which would have sufficed, a long
time since, to have formed the basis of new and im-
In answer to the question by "Iota" (page 22). I
proved tables? Suppose that a man had, in the year may tell him the announcement by Mr. Wray as to
1820, gone up the top of S. Paul's Cathedral in Lon-the separation of the close pair y Andromeda, by Mr.
don, and had taken a series of horizontal angles sub- Buckingham's refractor, was made in the "Astrono-
tended by the various visible church spires. Suppose, mical Register" for September, 1867 (page 201), and as
further, that year after year he published his results he speaks of the glass being "just finished," the obser-
to the decimal of a second of arc, admitting candidly vation referred to must then have been quite recent,
all the time that his theodolite was so abominably The central distance between the components of this
centered and badly divided that it could not be de-pair is commonly estimated at half a second. The
pended upon to read within 3 degrees! Assuming late Mr. Dawes' measure in 1863, was 0.59; most ob-
this, I say, should we not be a little disposed to laugh servers agree as to its being rather over half a second,
at our hypothetical observer, when, in this Year of although Mr. Browning, in his "Plen," says it is
Grace 1870, be defended the publication of such ad- under half a second. At any rate, the discrepancies
mittedly erroneous results on the ground that they are not great. I believe the two stars still keep about
might some day prove of the greatest use, in correct- the same distance, no widening having been as yet ob-
ing the theory of instrumental construction and ad- served.
ustments? I wonder what Sir Henry James would
say if he were restricted to such materials and

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solar observations at irregular times. These include
J. Birmingham, Tuam; Henry Pratt, Brighton;
Edmund Neison, London; Capt. H. Chichester, Far-
W. Blacklock, of Manchester.
town, Huddersfield; H. M. Whittey, Penarth; and

There are several gentlemen who intend making

position of its path across the solar disc, the time Should a transit of the suspected planet occur, the occupied in the transit, and its apparent diameter will be carefully noted. If the observer possess micrometric apparatus, measures of its position on the disc

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It is far more

POISONOUS POSTAGE STAMPS.] SIR. With reference to Mr. Denroy, I cannot help thinking that his friend's illness was not caused by the composition on the back of the stamps, which consists only of dextrine, or starch-gum; and so far from being unwholesome, is actually nutritious. likely to have been caused by some of the red colouring matter, which so easily comes off. quantity of stamps, some portion, more or less, would In wetting a probably be swallowed. By the way, do you suppose it is generally known that penny and twopenny stamps cost more to print than the higher-priced and more elegant varieties, the former being copper-plate printed and the latter surface printed. This seems a curious anomaly. Let me thank several who have answered queries of mine lately, and congratulate you on the improved form of our MECHANIC. A. S. Č.

EQUATION.

SIR,-" Hugo" rightly complains of my slip in not putting signs, but he has in the latter part of his letter overlooked the fact that I have not taken the square root, or why do I use the sign 2 As an excuse for carelessness I must plead illness. I sent a solution to the problem without revision, as I could scarcely bear to look at a paper, and hence this confusion. If "Hugo" will kindly wait a little, he shall

With regard to Andrew Johnson's inquiries on page
21, 1 should recommend him to read a little more on | have my ideas upon algebra.

C. H. W. B.

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TO MILLERS.

SIR,-I am a miller of 24 years' standing, and do not remember that I ever met with a scientific correspondence between men of my trade until I saw it in your MECHANIC.

With your permission I will make a few remarks on some of the assertions of your "dusty "correspondents. I am not too old to learn, and if I get hold of an idea that is erroneous I am thankful for correction.

J. Sharp says, in No. 258: "As to stones working well when out of standing balance, it only proves the stones are in running balance." I ask him kindly to explain, as I have a 10 ion that if the face of a pair of stones is true, the bedstone level, the driving irons and pitch of cogs of both driver and pinion correct, a standing and running balance are the same. My stones are balanced by Clarke and Durham's patent balance, and I have invariably found irons, face, &c., correct, after I had given them a perfect standing balance; the running balance was exactly the same. This I prove not only with a twig or chip, but I place a gas jet on one side of the stones when running, and go on the opposite side and look between them, when if there is the slightest variation in the face it may be seen.

But I have one pair of stones on faulty universal irons, and on them I find a standing and running balance are not the same; from which I infer that if the above conditions are observed, a standing balance will suffice. A boy's top, when not truly turned, or with a crooked peg, would scarcely spin upright.

If my memory does not deceive me, I saw, about ten years since, an advertisement of the "patent balance," and to me it conveyed the idea that millers were at a loss to account for their stones dragging when at work, and the "patent balance" professed to remove the evil. It is true many millers cannot account for it, looking only to the face of the stones for the cause, and forgetting irons, level, cogs, &c. This has often come under my notice, and surprised me. When I first saw the above advertisement, I said, "If a stone will balance standing, it will running," and I am still of the same opinion, after seven years' experience with the "patent balance."

Probably "Cumberland John" may glean a hint from the above.

With reference to Mr. Lomax's "Improvements in Driving Millstones" (No. 259), I cannot help but think it must be a great nuisance when taking out of or putting into gear the stones. I thought the fly-wheel was intended to keep the engine steady: if not, millers should take the hint, and take care their engine has two cylinders. "Prevention is better than cure." A STONEMAN.

INTERIOR OF PASSENGER CAR.

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Under the microscope it is seen to consist of oil globules of various sizes floating in a transparent fluid called serum or whey.

SIR,-In answer to G. Scott's queries, I beg to say that a pair of 4ft. French burr mill-stones (close), with 12 master furrows 24in. behind the centre, and two short furrows to each, ought to grind 16 stones per hour, going at 130 revolutions per minute. But the quantity depends upon the quality and condition of the wheat, and whether ground "high" or "close," and also if the exhaust is used. With respect to the wire machine, there ought to be 8 brushes in a 20in. Its composition varies considerably, being influenced cylinder going at 400 per minute; but the number of by the following circumstances:-The age and conbrushes is only a question of speed. I had a wire dition of the cow, the time and frequency of milking, machine at work about ten years ago; it was 6ft. long the quality of the food supplied, the housing, weather, by 20in. diameter, with 8 brushes; it had 4in. to the &c. Into these details it is not necessary to enter. foot fall (some machines have more); it made 400 The average per centage composition of pure milk is revolutions per minute, and dressed 6sks. of 20 stone as follows:each per hour. There were only 3 sheets of wire for Water 86, casein 5, butter 3, sugar (lactose) 4, fine flour, the rest was covered for white, grey, and mineral matter 1. The specific gravity is 1-030. brown sharps; the bran went through the end. In the above analysis the casein represents the If Mr. G. Scott is making improvements in his mill," flesh and force producer," and "force-producers"

which develop heat and mechanical force in the system consist of the butter and sugar.

than milk. The principal addition is water, but as Few articles of consumption are more "doctored" this has the effect of giving a "sky-blue" tinge and reducing its flavour, it is necessary to employ correctives in the shape of treacle or sugar for sweetening, salt for flavouring, and annatto for colouring.

Chalk, starch, sheep's brains, &c., are said to be also used; but this is very doubtful, as their presence would be betrayed by their insolubility.

The adulteration with water is easily shown by the "Gravity Lactometer." This is an instrument (Fig. 1) about 6in. long, and constructed to float at certain points, according to the quality of the milk. Thus the marking on the stem denotes as follows:-At W the lactometer floats in water; at M in pure milk; at 3, 2, 1, in milk containing respectively one-fourth, one half, and three-fourths water.

Another mode of testing is by ascertaining the quantity of cream yielded. Fig. 2 represents a glass tube about 11in. long, with a foot, and with the two upper inches graduated. The tube is filled up to 0 with the suspected article, and placed aside for twelve hours. The percentage of cream can then be read off. Although the quantity of cream yielded by milk is subject to much variation, yet we ought not to be content with less than ten per cent, from good milk.

Both forms of "testers" can be purchased at a small cost of the operative chemists and opticians.

The detection of the other adulterants is attended with some difficulty, and involves an acquaintance with chemistry and the use of the microscope.

BETA.

BUILDING AND STEERING VESSELS. SIR,-Although 66 Scrutiny's " query regarding sailing vessels, p. 579, Vol. X., was answered by " Cape Horn" (page 633), yet I think I can offer a few remarks on the subject which may be of use, if not to Scrutiny," yet to some of your young readers who may have a nautical ambition, and find a difficulty such us "Serutiny "complains of in his younger days, in getting his "lugger " to behave herself on a wind. We must not "despise the day of small things" in mechanics or nautical science any more than in religion, and therefore I will try to help others who are following the path of inquiry as I have done, from sailing models in the Serpentine some forty years ago, to the handling of Her Majesty's ships of larger tonnage than "Cape Horn" speaks of, but in all of which the same principle is involved, viz., the centre of effort, due of course to the masting and rig of the vessel and trim of the sails set; however correctly this problem may be solved theoretically when the vessel is upright, all is thrown out when the pressure of the wind causes the vessel to heel over, as Scrutiny" observes, the curve of the lee bow being increased while that at the weather bow is decreased at the float line, causing the vessel to rush up into the wind and requiring, as "Cape Horn "states, a good deal of weather helm to check and overcome; this action of "griping" as it is termed, is common to all rigs and all vessels, from a toy to a firstrate, and it is the perfection of seamanship to so adjust the "centre of effort, or "trim" the sails and hull of the vessel as to reduce this action to the correct proportion; as it is evident that if allowed to exist in excess, the leverage of the rudder surface required to overcome its force will seriously retard the speed and, in a storm, endanger the wringing off the rudder head; while, if it is totally counteracted, so as to cause the vessel to carry (as it is called by seamen) "a slack

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belm," there will be great loss of weatherly qualities |
and danger resulting from any sudden increase of wind
pressure which would strain the rigging aud sails, and
tend to plunge or press the lee bow deeply into a sea.
I cannot quite agree with my nautical brother
'Cape Horn" in his opinion that "the cause of ves-
sels not steering straight depends greatly on their
build." No doubt such is the case to a certain degree,
and the great nautical question still is, What is the
best shape for a sailing vessel? but I maintain that
the chief cause of bad steering in any vessel pro-
perly loaded to her proper displacement is, first, being
"out of trim," according to her lines or shape, and,
secondly, to the sails being not trimmed to the proper
angle, or judiciously distributed.

The first is of most importance in sailing before the wind and on a wind.

ADVANCING THE SHIELD.-INTERIOR OF THE TUNNEL.

replying to a question addressed to him, but which
seems to have escaped his notice.

"Novice," p. 607, Vol. X., states correctly enough that
the process of parabolising a mirror is usually described
as flattening the edge, but that the method described
by Mr. Purkiss seems to be deepening the centre. The
accompanying diagram may perhaps make this matter
clear to your correspondent. I may mention that a
precisely similar question was recently addressed to
me privately by a friend, so that probably the reply
will be useful to other readers of the ENGLISH
MECHANIC as well as "Novice."

Let A B represent a section of a speculum of spherical curvature, and let CD, CD, and EF, E F represent parallel rays of light falling upon its concave surface. The rays CD, CD, which fall near the margin, will have their focus at G, while the rays E F, E F, which fall near the centre, will have their focus at H, farther away from the speculum than G. The process of parabolisation has for its object to cause all parallel rays to come to a focus at one point, and in the instance before us this may be accomplished in two ways. We may work the polisher so as to act more upon the marginal than upon the central parts of the speculum, thereby flattening the edge and lengthening its focus, or, in other words, bringing out G to H; or we may

A

D

H

The second is of most importance on a wind and least before the wind. In large vessels it is the pride of her commander and crew to obtain the perfect trim of the sails, while it is the naval architect's pride to calculate correctly what should be the proper trim of the hull, and when these are happily combined a beautiful result is produced, for a full rigged ship in full sail upon a wind is a thing to admire." In sailing models, however, it is far different, as there is no one on board the little craft to attend to these points; and though it may appear childish to take up your valued space with such a subject, I maintain that it is not so, for the skill of the lad in sailing his little home-made model is really valuable experience, and may become the means of making him a good seaman in after life, and thus maintain our national fame and prosperity. I would therefore ask you, if possible. to allow me to say a few words upon Model Vessels," for the benefit of some of your younger subscribers and readers, one of whom asked a question on the subject some time back. All models for actual sailing should be rigged in what is called fore and aft rig, and have no square sails, so that should they by accident get on "the other tack," they may not become "hove to," as "Scrutiny" evidently describes from painful experience. Fore and aft rigs require the place of the mast or masts to be very correctly fixed, or they will never sail well; this can be very easily found by floating the model properly cause the polisher to act more energetically upon the ballasted, so as to trim by the stern considerably in central parts than upon the margin, thereby shortensome still pond, and there with a slight long sticking the focus of the central parts and bringing back push against her side till the point is found where she to G. In practice this method, which was introwill be pushed bodily away. The mast must be placed duced by the Rev. H. Cooper Key, is found to be the on a line with that point, or if two masts, equally most certain to produce the required result. distant from that line, and the head sails and bowsprit made considerably larger than the proper proportion in large vessels. The rudder must be fixed in the middle or amidships, and never moved. The whole attention of the young sailor being directed to the trim of the sails, by which the proper direction to the little craft's course can be obtained to a degree of wonderful accuracy, so that she can be made to run with the wind, or beam, or "close hauled," at pleasure. It is not so easy to make models sail more off the wind than a beam," and totally impossible to get them to sail" before the wind," which should never be the ambition of a British sailor, any more than it is that of the British soldier to retreat before an enemy. Many a valuable experiment has been solved by aid of the little sailing model, and i: bas often been a delight to me to watch the pretty little craft dancing over the mimic waves in our parks, as it has been to see my ship gallantly breasting the mountain billows of the ocean.

P.S-It seems to me that Mr. Purkiss is wrong in
placing the adjusting screws inside the cell, where he
cannot get at them without pulling the whole affair to
pieces. This arrangement makes it impossible to
perfect the adjustment under the eye.

ARTHUR W. BLACKLOCK, Newbridge,
Hardgate, Aberdeen.

SEA SICKNESS. SIR,-You lately gave a description of Mr. Bessemer's invention for preventing sea sickness. I understand that a model has been constructed which is stated to work admirably; but I believe this is like many other inventions, which work well as models, but are quite useless when carried out on a large scale. It is well known that the compass always preserves its level position, although it moves up and down and laterally with the heaving and rolling of the vessel; and it would be precisely the same with Mr. Bessemer's cabin. He seems also to have forgotten that the centre of gravity of the vessel, which is the point of PARABOLISING SPECULA. least motion (on which the cabin is to be suspended), SIR,-I trust that Mr. Purkiss will pardon my alters with every ton of goods shipped or unshipped,

THE ANCIENT MARINER.

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The

Mechanical skill has for many years past been engaged in trying to make our great servant steam work upon common roads. Two radical difficulties, however, baffled the ingenuity and zeal brought to bear upon the problem. Ponderous traction-engines were built on various plans, but always with the result that the shocks experienced in running over hard roads occasioned continual breakages in the machinery. But now the two difficulties have been overcome by the invention of the road steamer. road steamer can run on any kind of road. It runs over hard roads and paved streets without jolting, over soft roads without sinking, over muddy roads without slipping; nay, it needs no road at all, for it can run with equal ease over grass fields, through ploughed fields, upon ice, through loose sand, and over frozen snow. Though small and light itself, is climbs the severest gradients and draws enormous loads. It owes all its faculties and its exemption from the disabilities of other traction-engines to one device, as simple as it is efficacious. The wheels, which are of great width, are surrounded by tires of vulcanised india-rubber. These thick bar ds of indiarubber enable the road steamer to float over the surface of the ground without the slightest damage to the road, while they likewise protect the machinery from all concussion. The intervention of the elastic tires between the wheel and the road aets, in fact, in the same way as if the engine were running over a tramway of indiarubber. Mr. R. W. Thomson, C.E., of Edinburgh, the inventor of the road steamer, haying experienced much annoyance from the defects of traction-engines, and finding none able to do work for which he required them, conceived and carried out the idea of providing the wheels of a steam-engine to run on common roads with india-rubber tires of immense thickness. When the first patent road steamer was tried, some two years ago, its success was complete, and far exceeded the expectations and hopes of the inventor. Since then he has been engaged in building numbers of these engines to send to all parts of the world, and the record of some of their performances, in the presence of engineers, agriculturists, and other practical men, will doubtless be found interesting. A three-horse power engine drew a boiler weighing 13 tons up an incline of 1 in 12, the ground being so slippery at the time from frost that horses could not keep their feet. The engine was run through a grass field without leaving a track, and again through a field covered to a depth of two feet

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