This drawing is a back elevation of an astronomical clock with this escapement, three-quarters of the real size (not that the size is of much consequence). The train is the same as usual, except that it is inverted in position, so as to get the scape wheel at the bottom, and the wheel which turns in a minute now has 80 teeth, and drives a pinion of 8 on the arbor of the three-legged scape wheel. The scapewheel is behind the back plate of the clock frame, and on its arbor, between the plates, is a fly like a common striking fly, only larger; and the arbor of the minute wheel is made short, with its back pivot in a cock screwed to the front plate (with the screw-head in front) so as to leave room for a longer fly than could be got in if the arbor went through the clock frame.

In this drawing the pendulum is just leaving the right arm or pallet and taking up the other; and as soon as the stop is drawn quite away from the tooth now resting on it, the scapewheel will turn, and raise the other pallet by means of the pin which is now uppermost, until the tooth belonging to it is caught by the stop on that arm. If the are at which the pendulum leaves one pallet and takes up the other is called c, and the extreme arc a, each pallet ascends with the pendulum from e to a, but descends with it not only to c, but to-c on the other side of zero; and consequently the pendulum receives an impulse from the weight of each arm alternately through the arc 2c. The scapewheel evidently turns once round in 6 beats of the pendulum; and that gives a large enough motion at each beat for the fly to restrain its velocity, and thus prevent it from moving so fast as to jerk the pallet too far out, in which case the tooth may not be caught by the stop, and then the wheel runs on still faster, misses several beats, and perhaps breaks a tooth when it is caught by the stop descending again. This is called tripping, and has been the principal mechanical difficulty of gravity escapements. In my late Cambridge paper I have mentioned the various contrivances which have been resorted to to obviate it, and it is not worth while to repeat them here, especially as none of them have even come into general use.

Even those escapements which have been tolerably safe against actual tripping under any probable variation in the force of the clock train, have sometimes been liable to another miscarriage quite sufficient to injure the character of gravity escapements generally, and the more so because (as far as I know) it has never been noticed. Though the force of the scape-wheel may not send the pallet so far as to let the tooth slip past the stop, it may send it farther than it ought to go and would go if it were lifted more slowly, and then the pressure of the tooth on the stop is generally sufficient to hold it there; and the consequence is that the pendulum does not begin raising as soon as it ought to do, viz., at the arc c before-mentioned; and as the pallet will always descend with the pendulum to the same place, the impulse is increased, and the rate of the clock altered. In some of the gravity-escapement clocks in the Great Exhibition, I found that you could sensibly increase the arc of the pendulum in a few minutes, by putting some extra force on the clock train; which showed that they failed in the very first essential of a gravity escapement. In the three-legged escapement this is prevented by two things; first, by the fly, which moderates the velocity of the scape-wheel; and secondly, by the length of the locking teeth, the points of which are five or six times as far from the centre as the lifting pins, and therefore the pressure on the stop is so much less than where the lifting and the locking are both done by the same teeth, and is so little, that if an arm is by accident raised too high it will not stay there, but falls again, and the face of the pallet rests on the pin which lifted it, until the pendulum arrives and carries it off. The small amount of friction at unlocking also renders the pendulum indif ferent to the absence or presence of oil on the stops, and they require none, except just enough to keep them from rusting. Everybody who knows anything of clockwork

will recognise this as a point of primary importance in any improvement in escapements.

And this

All other gravity escapements that I am acquainted with involve at least as much delicacy of construction as the finest dead escapement. This, on the contrary, requires so little that it is hardly possible for a workman intending to follow the rules given for its construction, to make it so that it will not act perfectly. The makers of other gravity escapements too, even the best of them, never seem to have ventured to use a common train with low-numbered pinions and thick pivots; whereas, if a gravity escapement does what it professes, it ought to go just as well with a coarse train as a fine one. does so. The shortest proof of this is, that doubling the the arc of the pendulum. I know how difficult it is to clock-weight produces no effect, either on the time or on persuade clock-makers that any clock can go as well with which has been made under my direction, either for mya coarse train as a fine one; but every clock of this kind, self or other people, has been purposely made with a train no finer than that of a common house-clock, and the turret-clocks with all the wheels of cast-iron. Indeed, I caster, with a scape-wheel pinion of only six leaves; not saw one a few days ago, made by a clock-maker at Donthat I mean to recommend that, because such pinions cause a greater strain on all the wheels, and save very little in expense over pinions of eight. The first of these clocks of regulator size which was finished, was made with some old wheels, not even round, and brass pinions, and was sent to Greenwich by Mr. Dent (of the Strand), by desire of the Astronomer Royal, and submitted by him, as he told me himself, to some “malicious experiments," and it bore them so well that he concurred with me in authorising Mr. Dent to use it in the great Westminster clock; and it is well known to those who are acquainted with what he has written on escapements, that he was before under the impression that no escapement of this kind could answer.

In turret-clocks, besides the advantage of being able to use cast-iron wheels in the going part as well as the striking, there is no longer any occasion for long and heavy pendulums. That of the Westminster clock, which weighs 6 cwt. (I suppose, the heaviest in the world), had been made before this escapement was invented, or it would not have been so heavy. All the other large clocks which have been made with it have only a five-feet pendulum (1 seconds), with a bob of 150lbs. which is a considerable saving in expense in a compensated pendulum, and generally more convenient for fixing. This escapement also (like a remontoire in the train, which is more expensive) allows you to put on weight enough to drive the hands through any weather, without affecting the pendulum, as the escapement will bear three times the weight that will make it go, if it is properly made, without any risk of tripping. And I now proceed to give the rules for making it, which I have found from observation of several clocks, since my Cambridge paper was written, to be on the whole the best, with reference to various considerations, mechanical and mathematical; for the latter of which 1 must refer the reader to the aforesaid paper.

The distance of the points of the scapewheel teeth from the centre should not be much less than 1-6th of the length of the arms (down to the stops); and the lifting pins should be 1-36th of that length from the centre. The arc, which I have before called c, will then be about 45', or the pendulum will receive its impulse through 90′. The stops and the lifting faces of the pallets may be so adjusted as to make the depth of locking about 2-3rds of the distance of the pins from the centre of the scapewheel, or (in round numbers) 1-50th of the length of the arms. The arms should be only heavy enough to make the pendulum swing about 2° from zero. You need not be alarmed at seeing the pendulum have not much excursion beyond the point of unlocking; it is better that it should be so, because with this escapement the arc can never diminish so as to fail in unlocking, except from some accidental ob

struction to the pallets, and it is better that such obstruc- | tion should indicate its presence at once by stopping the clock, as it will, if there is only a small margin left beyond the point of unlocking. In astronomical clocks the length of the arms has generally been made six inches; in turret clocks nine, or double the size of the above drawing; but there is no particular virtue in these sizes. The bend of the knee in the legs of the scapewheel is determined by the rule, that the pins and the points of the teeth alternately should lie on the radii of a regular hexagon. The stop on the pallet, which is struck up. wards, must be set a little higher than the scapewheel centre, so that a straight line from there to the stop may form a right angle with the arm; for if the stop is lower than this, the blow will not be given in the direction of the arm, and will have a tendency to throw it outwards, which may as well be prevented, though it may not be enough to make the escapement trip. The other stop, however, should not be set so high as to form a right angle in the same way, because it will make the beats disagreeably unequal, and there is no occasion for it, as the action of the teeth on that stop, if set lower, is not to throw the arm out, but rather the contrary. The size of the fly in a regulator may be determined by trial. If you want a loud beat, you must have as small a fly as appears to be safe against any risk of tripping. In turrret clocks I find the fly should be not less than five inches long, by an inch broad, in each vane.

The scapewheel is made of steel not more than 1-8th inch thick in a turret clock, and of course thinner in a regulator; the pins of brass wire, rivetted in. The scapewheel of the great Westminster clock does not weigh half an ounce. The points of the teeth should be made tolerably hard, but not quite sharp. The stops should be screwed on soft and adjusted to the proper depth of locking and then made quite hard and polished; and the lifting faces of the pallets the same. The pallets of turret clocks may be of iron only faced with steel : in astronomical clocks they can hardly be made light and stiff enough unless they are of steel, and not above 1-16th of an inch thich, and about as broad as those in the above drawing. The lower ends are bent backwards at a right angle. to embrace the

beat-screws in the pendulum, the action of which is obvious. It is better not to put oil, as to the common fork, on the points of contact, as there is no sensible friction, and it may tend to stick the fork pins to the beat screws, and so resist the separation of the pendulum from the pallets; but the heads of the screws should be

made of brass.

In a short time I hope to be able to lay before your readers the results of the application of this escapement to electrical clocks, for which it offers great facilities; and for that purpose the drawing which I have here given will be wanted again, as I have as yet said nothing about the two pins marked e e. But before I finish this letter, I take the opportunity of mentioning a mode of regulating pendulums, which (as far as I know) is new in practice, and particularly convenient, especially with this escapement, which allows you always to set the clock right within one beat of the pendulum without touching it, by merely lifting one of the pallets and letting the scapewheel run forward, or turning it back, which will alter the time by any even number of beats you please.

If the ten-thousandth part of the weight of a pendulum is stuck on to the rod half way down its length, it will make the clock gain a little more than a second a day: that being the place where any given weight produces the maximum effect, and where any shifting of that weight up or down produces the minimum effect. Consequently, a sliding weight there is a bad way of regulating a pendulum; and on the other hand, if a collar is fixed there, and the pendulum so adjusted that it goes nearly right with some small weight laid on the collar, it can always have its rate altered by any assignable quantity, by merely altering that weight. The best way of making

a series of weights for the purpose is to try the effect of some weight large enough to accelerate the clock a good many seconds a day; then you will know what any aliquot part of it will do; and from that knowledge make a series of weights in geometrical progression, marked,, 1, 2 (these will be quite enough), according to the number of seconds a day by which they will increase the rate when laid on the collar, and therefore diminish it when taken off; which can easily be done without disturbing the pendulum. One ounce will do a second a day in a pendulum of more than a quarter of a ton, and 10 grains in the common mercurial pendulum of an astronomical clock. Yours faithfully,

42, Queen Anne-street, 10 Jan. 1854.

E. B. DENISON.

WILKINS'S NEW TELEGRAPH. SIR,-In your Journal for December 30th, 1853, you have a description of " Wilkins's New Telegraph," which is so erroneous, that, however I might pass over it in the journal in which that description first appeared, I cannot do so now that the Journal of the Society of Arts has inserted it.

The following would be a more accurate, and, I hope, more interesting description for your readers:-A point or marker is held by a spring in contact with a ribbon of paper against a marking surface, and if the marker were moved by the hand, lines of any form might be traced. The marker is mounted upon an iron armature between four poles of two electro-magnets placed vis-a-vis. The armature is fixed on a centre between the poles, and attracted each end in an opposite direction. The armature being at rest, equidistant between the magnets, it follows that while the ribbon of paper is travelling between the marker and the marking surface, a line is drawn in the middle of the paper, and any diversion of the armature from the position of rest entails a corresponding diversion of the line drawn, and by the number and form of such diversions the message is composed. automaton repeater connected with this telegraph is an apparatus devised to carry out the objects of Davey, (who to a certain extent succeeded to work a telegraphrecording instrument,) and to act as a relay of power to work other circuits. This instrument as now constructed, enables the longest circuits to be telegraphed over at once, without the operation of repeating. The telegraph is one would recommend it were expense only considered, but wired, and one operator only is necessary, this advantage the addition of greater certainty is secured likewise. The insulator is a means evident to the most ordinary capacity of accomplishing the insulation of over-ground wires. November, even at the present day, is the purgatory of telegraphs.

Yours, &c.,

The

J. J. WILKINS.

Contrary to the intention expressed in my last letter, I have decided, after some consideration, to complete the history of the flax plant in Ireland to the present decade, before giving any detailed account of recent improvements. In doing so, however, it is impossible to divide my subject

(a) It has been mentioned by Professor Hodges, in a paper the old Irish or Celtic name for flax is Lhin. on flax, read before the British Association when in Belfast, that This closely resembles the French Lin, the Latin linum, and the English lint and linen. It has been also stated that linen dyed yellow was much worn by the ancient Irish; and in the Brehon Laws the Brughaidho, or farmers, were obliged to learn and practice flax cultivation. (See Edward Campion's Annals.)

into any regular and progressive series, except, perhaps, that of time. I purpose therefore to continue to give, from the best authorities and in a condensed form, a statement of the events that have had an effect on the production or manufacture of the plant, or have been in some way connected with its prosperity.

The year A.D. 1816 was that in which Mr. Lee figured so prominently. The only interesting facts I find in the following year are-1st, a report to the Linen Board by one of their inspectors, of a tour through Scotland and Yorkshire, for the purpose of obtaining and imparting information; 2ndly, a published account from the House of Commons, giving a statement of all the importations of flax into Great Britain from 1807 to 1816; 3rdly, the printed instructions issued by the government, directing how the canvas for his Majesty's navy should be prepared. With regard to Mr. Marshal's report to the Linen Board, I may state that he gives an account of the cultivation of the plant in North Britain, and recommends the great care taken by the producers and manufacturers there, especially in the scutching process.

The following is the result of a trial made by him on Irish and Scotch flax, the former dried by fire heat, the latter by air :

"These parcels were hackled to the same quality for mill-spinning, and left a balance in favour of the Scotch of about twenty-five per cent. The reason of this difference, I, as well as those present, attributed to the firedrying of the Irish flax, by which it loses the oil, becomes hard, and the fibre easily broke. In Scotland the flax is air-dried in the field." (See Linen Board Report.) Mr. Marshal recommended the scutching-mill, for which a premium of £50 was accorded by the Linen Board of Scotland(a)

In addition to the scutching-mills the inspector advised the adoption, in Ireland, of a two-handed wheel for spinning; some of these he brought over; but about this time steam power and machinery were being tried for yarn spinning, and this tended to distract attention from the old-fashioned system of hand labour. It appears that so far back as 1793, mill spinning was begun in Scotland, but that the fluctuating prices for the raw material, from Russia and Holland, almost ruined the enter prising proprietors. This fluctuation was caused by the wars of the period, and in one year ranged from £30 to £150 per ton for the same quality of flax!

A desire was felt in Ireland to supply the Scotch manufacturers who were in the habit of buying the Baltic flax, and Mr. Marshal having inquired the cause of their not taking Irish, was told the system of kiln-drying, so much carried on in Ireland, and the fibre was so imperfectly scutched that they found, in these respects, it was interior to the continental, though, in some other points, it was perhaps superior; it was added that the shipments from Belfast were much the best in quality, and were rapidly improving.

The return of the imports of undressed flax into Great Britain already referred to is as follows:

Russia, and the chief part of the remainder from Holland and Prussia. As I will, on a future occasion, give some statistics of the present imports of flax, I shall leave this subject for the present, and at once pass on to the "Instructions for making his Britannic Majesty's Navy Canvas," which are dated from the Navy-office, January 1814:"1st. The chain or warp of the canvas to be spun from the longs of the best Riga flax, or the best St. Petersburgh 12-head flax (if free from blacks), or the best English or Irish watered flax. The flax to be well dressed, and free from any mixture of short flax, and the yarn to be well and evenly spun, and better twisted than has been usual heretofore. 2nd. The weft or shoot to be spun from the longs of the best Riga or St. Petersburgh 12-head flax (if free from blacks), and well dressed on the same hackles that are used for dressing the flax from which the chain or warp yarns are spun. N.B.-Although different kinds of flax are named, yet the Navy board reserve to themselves the right of restricting to either, as the quality of flax, or other circumstances may render necessary from time to time. 3rd. The boils are ordered to be made from American pot and St. Petersburgh pearl ashes." These are minutely described, and no operations of this kind to be allowed during the winter months. The rules extended to twelve, and were distributed among all the manufacturers for the fleet.

During the years 1818 and 1819, I do not find much of importance; the Linen board and trade appear to have gone quietly on with their routine duties. The improved scutching machinery, recommended by Mr. Marshal, was, to some extent, introduced into Ireland; a great many scutch mills, of the most approved class, were erected in different parts of the country, and among other parties that took an interest in this good work was the Drapers' Company of London, on their estates in the north of the island. Some seizures, I find, were made at various times of unsound flax seed, and an allusion is made to the demand for old Riga and Dutch flax barrels for the purpose of being refilled and sold in a deceptive manner. Early in 1820 Mr. John Wilson, of Dundee, attracted some notice to his invention of a new machine for dressing flax, which he styled (perhaps rather prematurely) "The Farmer's Friend;" the price was only five guineas; but it did not take," and soon sunk into oblivion. At this time a new measuring machine was also talked about, the proposal of a Mr. Coulter, and towards the end of the year a real genuine improvement was invented and carried out, namely, the new patent "temples" for weaving. In the old system rows of teeth were used to retain the web at its width in the loom; these frequently so marked the selvage as to give it a torn and imperfect appearance, which was very objectionable. To obviate this, a mechanic at Dromore planned a set of "temples" to hold the cloth like pincers, and not to puncture it in any way. At a meeting of the Linen Trade, in Belfast, a committee(a) was appointed to examine and report on the subject. The result was an order to the mechanic for 400 pairs for gratuitous distribution, and a strong recommendation to the Linen Board for a reward. After some delay he received £100. These temples are now in general use, and have contributed very much to improve the quality of Irish linen cloth. It is mortifying to think of the trouble there was in procuring any reward for this great improvement, and how much more easily the money was obtained for Mr. Lee. Perhaps it was thought "no good thing could come out of" poor Ireland, and that all useful improvements must of necessity be imported from other countries! On the 23rd of August, 1821, His Majesty George IV. visited the Linen Hall and Board Room in Dublin, and received a complimentary address. Trustees made some reductions in their expenses this year, but the Parliamentary grant continued the same as

The

(a) These names were B. Williamson, J. Charley. E. Curteis, J. Sinclaire, J. M'Cauce, A. Stewart, and J. S. Ferguson.