Secondly. I see no objection to having several arms, one below another, on the same post at a junction; but the top arm should invariably refer to the line going off to the left, and so on for the other arms.

distance varying between 800 and 1,200 yards from the box, the gradient principally determining the distance.

Whilst the loco. inspector surveys this flag frou a distance, the traffic inspector also looks at it from Thirdly. I think that if the home signal is placed the proposed (or existing) position of the signal-box, well to the rear of all siding and cross-over points and if each is satisfied that the driver on the one (as it ought to be), and the distant sigual three-hand and the signalman on the other will be abla quarters of a mile to the rear of that, that line to see the signal (as indicated by the flag), then clear" should be given when the train has passed that is all that is required, and the distance from well within the protection of the home signal: that box, height of arm (or arms), lamp (or lamps), and is, of course, if the man is so placed that he can see other particulars are at once recorded. the tail-board or lamp. "Blocking back," when shunting has to be done, is simply superfluous in these days of continuous brakes, if the signals are meant to be of any use at all, and causes unnecessary delay, especially where the block sections are long and express trains have to pass slow ones. Of course, the distant signals (and the home also, if any distance from the box) should have "repeaters" to the arms and lamps.

Sometimes the process of sighting is a nost difficult one, owing to intervening buildings, trees, bridges, curves in deep cuttings, and bad bickgrounds. This last is very important, and a sky background is obtained whenever possible, even at the expense of very high posts with duplicate arms. It may occur that a signalman is altogether unable to see the signal, and an electrical repeater is provided in the box to indicate when the signal has gone properly to "danger." On the other hand it may be impossible to get a good signal as seen front the footplate owing to a bad background (range of hills, buildings, &c.), and this difficulty is overcome by fixing a background of wood painted white 2in. or 3in. behind the signal arm.

A signal is sometimes erected on the (8) wrong side of the line to enable a driver to sight it some distance off, which, had it been put on the lefthand side, could not possibly have been seen until it

[22095.]-THE difficulty which your correspondent "Glatton" appears to find in understanding the mechanism of the obverse" tide can only be removed by taking into account the fact that is, the inequality of the moon's attraction on the two sides of the earth, the nearer and the more distantwhich causes the tides. Let us suppose that the earth, with its envelope of water, and the moon were the only globes existing, and that both were at rest. Of course, they would approach each other under the influence of their mutual attractions. I do not agree with Mr. Stretton's recommendaBut supposing this were prevented (as it is in nature tion about junction working. The junction signals by their rotation round a common centre of gravity), become little more than dummies, for the next still the figure of the waters would be that of a block signals in each direction are really made the prolate spheroid, with its major axis in the line junction signals, and the driver, on being allowed joining the earth and moon, and this in conse- to pass them, always expects to find the junction quence of the unequal distance of the opposite side signals at all right." Besides, delays are caused. of the earth from the attracting body. Now, that To give an instance. Hackney Downs Station, which would exist as a case of statical equilibrium, G.E.R., is a junction between two lines, and has exists also, and is unaffected by the dynamical cir-four lines of way through the station, so as to pass cumstances of the earth's and moon's motion. fast trains. There are stopping trains each way When we speak of the obverse tide being "left about every seven minutes, and express, local, and behind," we do not speak of this as a consequence main line trains several times in the hour as weil, of the earth and moon approaching each other, but so that it is essential there should not be the purely as a consequence of the quality of the slightest delay. For ten years after the opening of attractive power. these lines this junction was worked under the James Pearson, M.A., F.R.A.S. ordinary system without any accident occurring, Fleetwood Vicarage, May 2. and when the various trains were fitted with three ERRATUM.-I notice two errors in the otherwise different kinds of continuous brakes, or haud-L. AND N. W. R. COMPOUND ENGINES. perfect diagram which you have given in illustra-brakes only. Now all are fitted with the Westing[22699.-I INCLOSE names and numbers of the tion of the graphic process" for ascertaining the house brake. Yet a short time ago this junction last 10 L. and N. W. compound engines for the course of the tides:-1, the days of the month at was fitted with an electrically interlocked apparatus, benefit of correspondents who may ask queries the top of the drawing are each a day in advance; by which "line clear" cannot be given to the next about them and 2, the obverse path" of the moon is made to block stations on the two forks till the points are curve upwards instead of being the exact counter-set right for the coming train, and a train which part of the direct path."-J. PEARSON. would cross the path of another is stopped a mile

RAILWAY SIGNALLING. [22696.]-THERE are many dangerous systems in use on many railways which require alteration. One very dangerous plan that I have often noticed is in the pulling off" of the distant signals. If there are three signal boxes, A, B, and C, the signalman at B may "pull off the distant signal at A, indicating that the home signal at B is also off, and consequently that the line is clear from B to C, whereas the signalman at A cannot "pull off" his home signal owing to some obstruction between A and B. In the night-time this is excessively dangerous, as a long row of green lights, indicating that the signals-home and distant-worked from B, C, and D, &c., are all "off," may lead a driver to expect everything right, whereas the signal in front at A is not yet off.

This dangerous practice was illustrated recently on the Midland Railway at Wincobank. The signalman at B pulled off his distant signal opposite the box A, indicating that the line was clear between B and C; but the signalman at A could not pull off his home signal, which happened to be very nearly opposite to the distant signal mentioned, and on the other side of the line, because a goods train was shunting between A and B.

The above case illustrates another point. The driver of the train which came into collision with the goods train had to keep a look-out for two signals on different sides of his engine at once, one indicating line clear and the other danger.

As your correspondent, Mr. Stretton says, all signals should be placed on the left-hand side of the road, except where impossible to do so. When the signals are on the right hand, it may be possible for another train passing or standing on the other line of rails to obscure them.

Your correspondent also mentions the placing of the semaphore arms relating to different lines on the same post, one below the other. This is a very bad system, and can easily lead to mistakes. An accident due to this cause occurred on the L. and N. W. R. some time ago, but I am sorry I have forgotten the time and place.

In conclusion, I will ask some railway men to give us their opinions on the point. The opinions of engine drivers on a subject of vital importance to the public safety such as this ought to receive the fullest consideration, for it is they who have the greatest experience of them.

Meteor.

[22697.]-I SHOULD like to make a few comments on Mr. Stretton's letter (No. 22611).

First. The distant signal should interlock with both home and starting signals, so that it cannot be lowered till both the others have been. Thus, a driver on passing a distant signal at "all right may go on in perfect confidence, even in a fog, that the way is clear through the next block.

away.

Thus constant delays arise, and the splendid regularity which formerly prevailed is upset.

There is one very important point which Mr. S. does not mention-viz., colours of lights at night. Red, of course, should be the danger signal, and green or blue the "all right." A white light should never be used, but should be taken as a danger signal, for it may be shown as the result of the breakage of the red spectacle; but I think distant signals should be distinguished at night as they are by day. Perhaps a small spot of white in the centre of the red glass and a purple glass might do.

The G.E.R. a few years ago went to great expense to fit green glasses to all their signals; but a few months afterwards these were removed from the distant signals, with the intention, I presume, of distinguishing them; but with very great risk in my opinion, for this is the most important signal in bad and misty weather. The Mid. R. still retain many of their "board" distant siguals here (London), and till quite recently many of the points were worked by wires, causing frequent derailments. I never saw this plan on any other line.

F. S. H.

[22698.]-I SHOULD like to offer a few remarks in reply to Mr. Stretton's letter (22611) re above, as it is extremely likely to convey a false impression to the great bulk of your readers whose knowledge of the subject is not sufficient to enable them to judge for themselves on which lines the system, or want of system, as the case may be, prevails as to the positions of above.

Mr. Stretton regrets that on some lines the signalling arrangements are placed in the hands of a separate department, and attributes the want of uniformity to that cause. I think he should put it the "other way about," as the positions, &c., of signals will be found most defective where the subject is not made a study by a separate and responsible department, but is undertaken by the district engineers or permanent way officials.

On the North-Western line an efficient system is in operation. All plans of signals, locking arrangements, &c., are prepared by skilled officials. No new signal is erected or the position of an existing one altered until a meeting upon the ground has taken place between the inspectors from the signal, locomotive, and traffic departments, who mutually agree upon the position, height, distance from signal-box, side of line (left-hand, or driver's, if possible), and all other particulars required to make the proposed signal an efficient one.

sighting" signals the distant" is looked upon as the most important, and the first consideration is that the driver shall have a distinct and distant view of it. To enable the drivers' inspector to determine this, a flag is elevated at the end of a long staff (several staffs are provided so as to elevate at considerable heights if necessary) at a

was reached.

This much in fairness to one company, and to prove that on at least one line the drivers are properly represented, and that an efficient system can be carried out if the departments interested mutually arrange the details.

Traffic.

311. Richard Francis Roberts. | 353. Oregon. 315. Alaska.

363. Aurania.
365. America.
305. City of Chicago.
310. Sarmatiau.

$21. Servia.
223. Britannic.
333. Germanic.
There are now 20 of these engines. The uime:
of the other 10 have been given before.

Meteor.

THE FRONT-SLIDE LATHE. [22700.1-I OWE apologies to "F. A. M." and others for my rough sketches of their beds, but there was no intentional caricaturing; I meant merely to bring into one view the various designs, as a help to forming a decision, with no thought of anyone taking them as exact. I added the dates to my sketches, which, however, did not appear, so as to enable anyone interested to refer to the originals. I add it now for ease in reference. Fig. 2, O. V., Dec 5, 1853; Fig. 3, "F. C.," Feb. 15; Fig. 4, Mechanicus," March 7: Fig. 5, "J. H.," March 14; Fig. 6, "F. A. M.," Much 14. That no partiality was shown is, I think evident, for my own bed has fared as badly as any.

I had hoped something might have been doue in to-day's number to settle the best form. For myself, I give the preference to Nos. 3 and 5, these being the only two which avoid the chip and oil difficulty. Of course, F. A. M.'s" does so, but as a modification of mine, for reasons first given by myself and afterwards repeated by Mechamcus," I cannot approve of it in any sense. I am Lot now speaking of the bracket and saddle, for J. H.'s" bracket is similar in design to O. V.'s" and the York firan's, my bracket being detachable, and intended to slide vertically on the saddle face, as stated in my letter of Feb. 15, and as worked out more fully in "F. A. M.'s" drawing

66

That the same idea of the vertical slide was present to his mind at the time I wrote is evident. With sharper and plainer tables before our eyes, the originality of the idea is not very great, and, therefore, my priority in publishing it is not worth talking about: but it has been in my mind for more than two years-first suggested by Major Armstrong's bracket.

may say that I prefer No. 3 to 5, or, for that matter, to any of the others. 1st. Beuse it is stiffer in every sense (pace Mr. Brockley), weight for weight, fully 50 p.c. to any of the others. 2nd. Its construction is simplicity itself. 3rd. It is free from the oil objection, which "J. H.'s" is not.

Now, to say a word as to the objectious lately made to my form-1. Difficulty of fixing heads, &c. Reference to Major Armstrong's letters, Vol. XXXIV., will show the method I would adopt. It does not require poppet to be slid off at end, and has some special advantages. My sketch of the fixing in letter, Feb. 15, was not intended as more than showing the general idea of poppit base. There are several other ways the thing can be done, which need cause no great difficulty; and so

fitted, there could be no greater tendency to get the head out of line, as "Mechanicus" seems to say. 2nd. Truing the internal V would be somewhat more difficult, but not so much so as to condemn the form. What I do feel is the objection which "O. V." pointed out the centres on which the rest would turn when under a large diameter cut would be the lower V. But the idea I had from the first was that part of base of slide-rest would slide on top of bed, and thus the whole strain would not be on the slides. This would be the state of the case in nine-tenths of amateur sliding or screw-cutting. In turning large discs it would be easy and desirable to clamp the sole of rest to the back side of bed top, thus removing all strain from saddle and slide.

Mr. Brockley objects, with reason, to the loose strip being above. I put it there especially to allow as much depth as possible to the gap. It may, and probably would, be better below. As to the weak point in the bed referred to by him, I must decline to admit it. He may be coufounding my form with F. A. M.'s," in which the web is not sufficiently stayed. but in mine it is so.

As to Mr. B.'s own form of bed, given in today's, as he is so nervous, perhaps I had better not make any remark on it. It is a modification of "J. H.'s"-whether with advantage I leave others to say but, judging from the sketch sent, I would say he hardly makes good claims 1 and 2.

A word to F. A. M." I am not blaming him for passing on to the side saddle, with its vertical slide. I did so myself before he wrote at all; but what I say is, it would be better if we could settle definitely on one or two forms of bed as the best, and then drop the bed question and give undivided attention to perfecting the vertical rest. It seems to me we have too many irons in the fire.

F. A. M." seems to think that my bed is only a paper one: that it is easy to set out a nice section provided only it is not to be put to use; and that I have not tried if I can get my nut in. This is not the case. I find I can, without difficulty and even if there was, I see no objection to its being fitted at right-hand end of saddle. In his design it seemed to me much unnecessary space was wasted.

To Mechanicus" I should say: It was his speaking of "overhanging lathe heads" I misunderstood. I see his meaning now. "The tempering business I do not see the way through at all. Of course I can see by his concluding remarks that he desires me to feel a very black sheep, which, by the way, do not feel. If our ideas are worth anything, they won't be blown down by a breath of wind. As to combination tools, I had been noticing how the times have changed. I remember-to use a vulgar word-how I was "sat upon for venturing to say what he has

said.

In answer to Me hanicus's' queries, letter 22610:

1. The central position of heads will, in front slide lathe, cause his strain to come on the V's, whether internal, as in my form, or external, as in

most of the others.

2. Fixing heads on my bed may be as per Mr. Armstrong, or as suggested by yourself below. By either plan it is not necessary to slide poppit off at

end of bed.

3. I would, if "J. H." had not said against it. say: Certainly have mandrel head cut with bed, giving the same reasons as Mechanicus" himself. April 25.

Fredk. Carre.

THE FRONT SLIDE LATHE.

[22701.1-My letter of April 26 I forgot to post. I now add a few lines by way of postscript. I am glad to see that my suggestion has been taken, and "J. H." I have to thank very sincerely for his attention to my request. I think his dimensions for my form of bed are very good. The giving it a wider, and not merely thicker, bottom flange is a decided improvement.

that four writers have recorded their votes.

total rejection. Patterns for the others would cost
a good deal of trouble.

I do not quite understand "F.'s" proposed
amalgamation of 3 and 5. Is there a mistake in
the use of the word "brackets"? If he means
front top flange of 5, to be made the same as top of
3, I see no objection to it. What does "J. H."
say to such a modification? It will certainly give
the stiffness of the single-girder bed, and make the
casting lighter-and patterns quite simple to make.
Would J. H." look into the matter, and give
us dimensious of his bed No. 5? His orginal sketch
was a mere outline, and my copy was not an im-
provement. My fear has been that, to get cover
for his slide, the width of slide must be consider-
ably curtailed, or else the bed made very deep.
Does "Finem Respice" not consider it any ad-
vantage to be able to move saddle out of the way,
without unshipping anything, when hand - rest
has to be used?

Mr. Bear must not be in too great a hurry. My
initials will allow me to assume the name of
"Fabius Cunctator"! I do not think the matter
is thrashed out yet. Chiefly because we have been
waiting and hoping for more assurance; and from
quarters we have yet heard nothing from. I saw
Mr. B.'s two advertisements, and was about
drawing attention to them; but did not think we
had yet come to the stage of putting the matter
into the manufacturers' hands. I do not wonder
the two who replied to him did not know exactly
what they wanted. It may be an unreasonable
thing to do; but still many people expect manu-
facturers to show them what they want. Mr. B.
has popped us somewhat, but perhaps hardly as
much as he might. He only now tells us he disap-
proves of all our plans, and cannot give us a gap.
At least that is how I understand his letter.
May 3.

Fredk. Carre.

diagrams of the different forms proposed, is very
[22702.J-MR. CARRE'S letter (22606), containing
convenient for reference. My own opinion is in
favour of Figs. 4 and 5, modified according to
circumstances. The top ledge or carrier rail is,
the outer, as shown in Fig. 5; the wear of the
perhaps, better sloped on the inner side, and not on
pieces will then tend to keep the sliding faces in
have a gap in it, because, though it is an easy
contact. Probably many would prefer the bed to
matter to raise up the headstock, the fixing of the
rest is not so readily accomplished, whereas if the
work can run in the gap, the slide-rest can be used
on it without any further fixing.

I still think the exterior V's are preferable to the
inner ones, because, the weight being supported by
the top V, there is a natural tendency for the faces
of the bed and carriage to keep together, and the
lower V-piece has little else to do but steady them.
Hence I think it would slide easier, and yet with
the strain of cut, and the lower one the weight to
more firmness, than when the top V generally has
carry. Were it not for this, Fig. 6 has certainly
the preference for compactness and simplicity.

gap bed, low down, the pull for traverse is such
that it has a manifest tendency to drag the saddle
in an angular or rather lifting manner, as would at
once appear were the ribs removed, while in a
front slide, the pull being in centre of saddle, or
directly in the line of its required movement, this
objection or effect would not only be altogether
removed, but also a less power would suffice to
remove the saddle. I should like to hear the
opinions of your many correspondents on this point,
and would also be glad if any of them can say why,
and for what reasons, the U.S. practice in lathe-
building differs so much from that of England-
e.g., here all leading screws are either 2 or 4 to the
inch. U.S. lathes, 5 for large-power lathes, 10
for small-power ditto. Certainly the finer the pitch
the less the power needed to move saddle. Also in
mandrel noses: the U.S. lathes of, say, 9in. centre
lathes, are cut 8 to inch, and that of a large milling
machine (Brainard) 24in. diameter is 10. This
fine pitch tends very much to increase the difficulty
of removing a chuck or face-plate after a job has
been taken off it, and so the face-plate is solidly
bedded by the pressure.

I think that there are many other points in U.S. practice which might be ventilated with advantage in your columns, and, if desired, will refer to them again. For one thing, no lathe is saleable there which has not an arrangement, better or worse, for adjusting height of tool point-a matter of absolute ecessity in the case of a parting tool. This seems to be quite overlooked by English builders.

H. E. K.

[22704.J-HAVING read with much interest the discussion on the F. S. L., I wish to bring before your readers a plan of bed which would have advantages over slide on side of bed, although taking up more room in front. I inclose sketch of bed in

Aberdeen.

G. W.

I do not see

Next, as regards the V face in Figs. 4 and 5, the overhanging ledge need only deepen the bed by about half an inch; but is this ledge a necessity? If the oil and chips are so troublesome, could not the pieces which unite the V's to the bed have long narrow holes cast through them at intervals, through which the chips might drop? And this section, with the heads off, the centre being placed brings us to the question whether it would be nearer to the front. advisable, in any case, to have the V's cast in a detachable piece, which could be planed and screwed on the bed. An ordinary form of bed might in this way be converted into a front slider, [22705.]-I HAVE carefully studied the section and I seem to remember having read of someone for lathe-bed proposed by our friend "Brockusing this plan to make a common lathe into a ley," and give my opinion as desired. I must screw-cutter. If the requisite accuracy and solidity honestly say I do not like it. To me it appears to can be obtained in this way, it would make the bed be, not a step in advance; but otherwise. It would between the bed and the V-pieces for the turnings would have to be cored, as well as the recess in much easier to cast, and then holes might be left would be a most awkward piece to mould, as I imagine that all the spaces between the shears to fall through. But if the 1-slot shown at the top of Fig. 4 has not proved troublesome, I do not front slide for screw and clasp nut. see why the V channel should, provided it is made the necessity for the back shear at all; but as some deep enough, and rounded at the bottom. If, of our correspondents appear wedded to the old however, the V be covered, it certainly looks more (double) plan, some deference must be shown to compact, and out of the way of injury; and if it their opinions and if this is to be adopted, by all it is better so. can be done without making the bed unduly deep, means let us have the bearers vertical. I think we The lower V-piece need only be are pretty well all of the same opinion that in this about half the strength of the upper one, because (outside V) form the most severe strain will always I think he is quite right that there need be no there is very little strain on it; but its face should be taken by the back of top V of front slide, aud difficulty anticipated in fitting poppit, &c., to either not be any less, in order that equal surfaces may be also by the lower flat, the top one having very little his or my section of bed. Either of his Figs., but exposed to wear. Fig. 2 by preference, would do very well. Has he be lowered sufficiently to allow a ledge to project, ley" has the top V inside or bearing-surface much In Fig. 4, if the whole V-face to do, and the lower V merely acting as a guide, and means of taking up. Granting this, "Brockseen Major Armstrong's proposed method? In and the upper carrier rail (shown square in the some ways it is a great convenience. I experienced figure) be sloped down on the right-hand side, I do too small. The upper or top front flat might be it to-day, when having to cut a screw on a cone. not see why it should not be a useful and convenient reduced, and the lower one (which has almost as This can only be done otherwise by having the much to bear as the top V) be widened, or it might cross slide geared. even be left as it is; but by reducing the top flat we should gain more space for the clasp nut, and whatever else may be wanted there. My first [22703.]-IN the recent letters regarding the thought on seeing the proposed section was to unite various differences of value as between a "front-the back shear and back of bracket or front slide slide" lathe, even as ordinarily made, Whitworth's something like inclosed sketch, reverting neces alone excepted, there appears to me to be a point sarily to the longitudinal slot, or a modification o altogether overlooked, which is this-viz., that it, which, I am convinced, will, in the end, b whereas in any ordinary top-slide lathe of which found most suitable for this class of lathe. Core the screw is in frout, or more particularly with a 'holes, of course, would have to be provided to clea

It agrees with what I had drawn for myself, except in the wider base and in. more metal in the web. I presume "J. H.'s" is the finished size. What I wrote last week will answer "F. A. M.'s" reference to his form of bed. There is room for my screw and nut.

I am glad "Faber" approves of my election idea, and that he has recorded his vote. Why I like No. 3 bed is on account of its simplicity and great strength and stiffness. In half an hour you could make the pattern, whereas though I do think No. 5. and those with the external V's all are better, in the way the saddle can be swung. Still, I think, notwithstanding the objections which may be made to my form, they are not so serious as to cause its

form.

April 25.

Orderic Vital.

away the chips and turnings, and I propose to do this in a manner which will not in any way weaken the bed. I objected, in my last letter, to the leading-screw being placed either far out in front or back of bed, or so low down as in all gap lathes, and gave my reasons why. The same applies to having the rack at bottom of bed-why not use the leading screw for running saddle or bracket to and fro? I have used, and still do use, this plan successfully, without perceptible injury to the screw, and by so doing I obtain an additional motion in front which can, by intermediate gear, be communicated to traversing screw either for surfacing, or cutting spirals, or scrolls, for the new lathe I am designing. I intend using only a long half-nut supported above or below (as the case may require) by a long semi-cylindrical guide accurately fitting outside diam. of leading screw, and about 6 diameters in length. The 7in. I illustrated last week is fitted in this manner, as also my own little 3in., and I can assure all those interested in the matter that it is an excellent arrangement. "Brockley" has also adopted the plan

of covering the top V. Now I have in previous letters stated that I think such protection quite unnecessary, beside which it has the defect of obliging the designer to place the very point (the top of V) which ought to be as high as possible, all so much lower down as the thickness of cover, and so increasing the strain on bed by increasing the leverage of saddle. I said in my last letter, that I should propose the front edge of top bed to be a V. I find, however, that I must abandon that plan, else the poppet head can not pass the saddle or bracket, unless the whole front slide is lower in such a manner as to increase the leverage as above stated, and to which I strongly object. For my own part I prefer the girder form of bed (perhaps because it is, I believe, my own) as being the simplest and, I submit also, the stiffest;, besides which, "F. A. M.," "O. V.," "F. C.," and I think others also advocate it. However, let each of us give his opinion which form is to be adopted, and let the majority decide.

I suppose the proposed section is for a 4in. centre and in. per inch scale: the sketch inclosed approaches very much to the one I sent some time

ago.

I forgot to answer "Brockley's" objection, in the third paragraph of his letter, as to the wear on the back flat of top V. Now the bracket and saddle in this case are in precisely the same conresponding parts and tool-box of a planing machine, and I propose to fit them in the same manner. If the arrow a (see sketch) represents the weight of bracket, slide, and stress due to work, it is evident that such is taken imprimis by the top edge and back flat of top V at c; half of this strain will then become horizontal and act on the bottom front flat in the direction of arrow b. Now if we take dot d to represent the point of a planing tool, and arrow e the direction in which the work is travelling, this last imparts all the resistance due to the cut through the tool, tool-box, &c., to the aforesaid lower flat of slide with a force equal to dex d b, and the pull forward on the top back flat c d of my section at would be equal to There would be, in the case of the top V being at the back, also a tendency of the saddle to slide up off it, which, however, would be counteracted by the bottom V and loose strip. In planing machines the top channel on saddle is generally planed a trifle deeper than the standing of the slide, or a thin strip with pushing screws is fitted at back to take up wear. With this form of slide, the saddle might simply hang on the top V, the bottom one only serving to prevent it lifting off its face, and to take P.S.-There are two misprints in my letter on "Lathe Matters," April 25-viz., p. 168, line

dition and under similar strains to that of the cor

up wear.

bc.

10, middle column, "mark" should read work;
at 5th line under section of lathe bed, in same
column, "collar" should read cotter.
Mechanicus.

AMERICAN SCROLL CHUCKS AND
FRONT-SLIDE LATHE.

[22706.]-I DISAGREE with "O.J.L." in his opinion
of scroll chucks running untrue. My 4in. chuck runs
as true now as it did when I first mounted it, two
years ago. The chief defect is that much difficulty
is found in making it hold work tight enough. As
regards the stretching of the holes, I used the levers
supplied with the chuck, and as there were not
enough holes I drilled three more, and it is these
that stretch the most. I have taken work off the
chuck and have replaced it, and it ran as true as
before; but this may be because I make a mark on
the work corresponding to one on the chuck. My
2in. chuck runs untrue, because the lower ring is
cracked, but from nothing else. If I had a lathe
that would cut the scrolls and the teeth on the jaws,
I would not be slow in making a 'cheaper and more
satisfactory chuck.

In regard to the front-slide lathe, I do not think that any of the designs that have appeared get over the chip difficulty. Grooves collect chips and grits unless well covered. Of the best form of bed for front slides, the girder form, I think, is undoubtedly the best. Of the seven sketches in letter 22606, Fig. 6 is the one I like the best; but it has a weak point in it, which I remedy in my sketch. The top flange of bed should not be more than 3in. wide, and the lower one 24in., leaving lin. to

cover the slides. The sketch is not made to scale,
not be high enough.
but only to illustrate my idea, and therefore may

It appears to me that the girder form of bed
cannot be made with a gap, for I should think it
would shake and vibrate. Is this the case or not?
Dresden, April 25.

A. F. Shakespear.

ORNAMENTAL TURNING-THE

I

STANDARD MANDREL.
[22707.]-IF "A Member of the A.M.S." will con-
sult the Council Minutes" published in the last
number of the Journal, I think he will see that his
statement of how the business stands," is not
quite accurate. The general meeting (10th May,
1882), did no more than refer the matter to the
council without special instructions. The council,
by resolution 11th Oct., 1882, approved aliquot
threads, and proposed to elicit by circular the
opinions of the Society on the adoption of Whit-
worth threads. I was not one of the four members
who passed that resolution, and when, on April 11,
1883, Dr. Edmunds read a draft of the circular,
observing that it went far beyond the terms of the
resolution, being in fact a statement of his case,
thought it undesirable that this should go forth
alone, and it was eventually decided to lay the
whole question, pro and con., before the members
in a special number of the Journal; thus, virtually,
though not formally, superseding the resolution of
the 11th Oct., 1882. Such a number was accordingly
issued, accompanied by a series of interrogations
intended to take the place of those prescribed in
the resolution of 11th Oct., 1882. Up to the
present time, therefore, nothing but the method of
procedure has been determined, and it is incorrect
to say that the council have finally determined to
recommend the adoption of aliquot threads, or that
they have approved Dr. Edmunds's thread form,
for, although such a resolution was passed, it was
rescinded at the next meeting on the ground of
informality.

one.

fine for the ordinary sized 5in. mandrel, and if so
it would be much worse for Dr. Edmunds' larger
I do not propose
"to keep two sets of screw-
threads going," nor, so far as I know, does Mr.
Burnaby: he and I have a sufficient number of
threads of all sorts at our command for binding
and other purposes, and whenever we do want an
aliquot thread, we can go to our Holtzapffel
lathes and produce one without the smallest diffi-
culty. It is Dr. Edmunds who wishes to add
another thread to our already abundant stock, for,
if the council determine to make a recommendation,
and if the lathe makers heed it when made-two
very important “if's "-that will not get rid of
the necessity for keeping these dreadful threads in
stock, in order to meet our requirements, and those
of the numerous other possessors of existing
lathes.

I do not know what the average life of a lathe
may be; but I have an impression that if Dr.
Edmunds could deal with the future as he pleases,
leaving their owners in undisturbed possession of
present lathes, his millennium would commence
somewhere about the end of the next century!
April 5th.
T. W. Boord.

[22708.]-I REGRET that other work prevented my replying last week to Mr. Boord's letter. In the two other letters from members of the Amateur Mechanical Society I cordially agree, and we are much indebted for these contributions to the elucidation of the subject.

The ground on which Mr. Boord now seems to stand is that, although the chuck-boss did fit my mandrel very perfectly, "that proves nothing.' But all that I had to do was to refute Mr. Burnaby's dogma as to the impracticability of fitting a chuck to my mandrel, and, therefore, I think it proves something. The pub'ication of extracts from personal letters or conversations is generally misleading, and in this instance is so. Such publication is obviously an inadvertence. If I could permit myself to follow the precedent, I should have to publish the foolish things which have been said by the opponents of aliquot screw threads and other improvements. Other points remain, which I must leave as matters of personal equation. Those who wish to see who has read the data most accurately may refer to the quotations. Meanwhile, I turn to points on which this discussion can be made to serve scientific progress in the tools used by scientific and artistic amateur turners. As Faber says, we have three classes of such amateurs: Those who use their mandrel head simply as a dividing engine for circular arcs in the disposition of ornament upon lathe works. Those who also use philo. sophical instruments, and who want occasionally to construct, repair, or alter a microscope, a telescope, or other scientific or mathematical instruments. Those who amuse themselves with fine turning, pattern-making, and metalwork properly so called, and who use their lathe as a universal jobbing tool.

General Clarke, in his critique, states that he has used a Holtzapffel lathe for more than forty years, having comb-tools to match each screw-guide, which is all he finds necessary, "without knowing or caring how many threads to the inch each gives." Mr. Boord tells us that he has used a Holtzapffel lathe for more than a quarter of a century, and that "neither the fractional pitches, nor the different denotements of the same thread have been a stumbling block, for, having only used the screws for the purpose for which they were intended, I have had no occasion to inquire into their pitches, or whether they bore any relation to each other." And Mr. Boord goes on to give, as an illustration of amateur work, the fact that he is at the moment building himself a photographic camera, and requires a new flange for a large lens by Ross. The screw is about 4in. in diameter, and the thread declines to agree with any screw-tool in his possession. On measurement with a fine-pointed pair of compasses, from the bottom of one thread to that of the next, the threads appear to form part of a screw of 11.76 threads to the inch, in which case he will want wheels of 49 and 25 teeth to cut the counterpart thread. But it is difficult to measure SO small a portion of a screw accurately, low and much rounded, so he will first try a 12 especially when, as in this case, the thread is shalthread screw (on a piece of boxwood). If that will not do, he is to cut a pair of special wheels for the purpose. This will no doubt delay his work, but it will furnish him with equal amusement, and be on the whole preferable to abusing Mr. Ross for selling a lens with an incommensurable thread.

serious in thinking 9-5 better than 10 threads to
I can assure your correspondent that I am quite
the inch for the mandrel nose of a in. lathe. I
have a 10 thread and a 9-45 (Holtzapffel) mandrel
in use, and I infinitely prefer the latter. The
reason is not far to seek: if the mandrel screw is too
coarse the chucks will not fix properly, if too fine
they will "jam"; my experience leads me to
suppose that 95 is the most satisfactory pitch,
This is what Mr. Boord tells us. I joked him
avoiding both inconveniences, and I imagine that upon his goodness in providing me with such mate-
if the Holtzapffel threads could be swept away as rials as the above, and this joke he innocently
completely as Dr. Edmunds desires-so that neither publishes, at the same time expressing his surprise
they nor the tools for their production remained that my comments upon his paragraph are so
Messrs. Holtzapffel would adopt that pitch to re-feeble! To other readers, my adding one word of
commence with. But why should it excite derision? comment upon such material as the above would
It is one of those enumerated by Dr. Edmunds as have been like "painting the lily." There is evi-
being easy of production (vide Table IV. on p. 29, dently a vast "personal equation" in the point
4.M.S. Journal, No. 25). I know 10 is rather too from which amateur mechanical work is looked upon

ENGLISH MECHANIC AND WORLD OF SCIENCE: No. 998.

usefulness of the ENGLISH MECHANIC, than by
endeavouring to make it still more generally
We cannot better express our appreciation of the

by different members of our society. We have dis-
covered a new physiological fact-i.e., that contact
for 40 years with a Holtzapffel mandrel-nose of
9:45 threads to the inch has the effect of case-known.
hardening its owner's cerebral matter. In presence
of this discovery, I will no longer attempt to con-
vince my critics either by fact or by argument.
I must leave the matter as one of
equation"; but I dissent point-blank from their
personal
doctrine.

The ornamental-lathe threads of 9:45, 13:09,
19-89, 25-71, 28-88, 36-10, &c.; the photographic
threads of 11.76 to the inch, &c., et il genus omne,
are one and all part of the milch-cow business-a
system by which amateurs are humbugged and
victimised, and it is the duty of every one to protest
against the maintenance of such a system of
trade. If the Amateur Mechanical Society had
been founded in order to kill time, and to whittle
away ivory and blackwood, my proposals would
be revolutionary. But that is not so; and all we
ask is, that our eminent Associates, who con-
scientiously restrict themselves to ornamental whit-
tling should kindly bear with those members who
cannot fully amuse themselves in that line. Aliquot
threads will be as available for whittling away
ivory and black wood as the present fractional
threads. Nor will the innovation we propose limit
in any way the propagation of fractional threads
by those who delight in their multiplication. Why,
then, should not the society fix upon a standard
mandrel-nose, a pro. erly-defined thread-form, and
a series of aliquot thread-rates which can be used

?

MAY 9, 1884.

wine half water?
order to get the mixture in the wine bottle, half

SOLUTION.

to a higher sphere of usefulness by the intercourse in it will be = 20 Q'ounces, and proportion of
of many minds, and the help and encouragement
As we ourselves have been benefited and raised
Suppose at any moment amount of wine in
wine bottle=
our part to extend its help to others, and spread its
we have derived through its pages, so let us do wine in mixture will be
Q ounces, then the amount of water
influence into every mechanic's home.
Q An ounce of this will,

number of workmen, who do not now take in the
paper, may be the means of largely increasing the
A single copy of the MECHANIC sent to a large
weekly circulation.

men who are likely to be interested in the journal,
and I beg to suggest that we should, one and all,
Each of us must know a number of fellow work-
send to the Editor a list of names and addresses,
where we should like the MECHANIC sent, inclosing
remittance for the amount. It appears to me a
fitting occasion for the distribution of a very large
number, and if the Editor will acquiesce with us, let
us at once signify our intention of joining in the
scheme. We may accomplish a lasting treat to our
chums, and a permanent support to the paper, at
little cost to ourselves.
O. B.

therefore, contain Q

20

20

the water bottle the amount of wine is evidently (20 ounce of wine. Now, in that the proportion of wine in water bottle is Q) ounces (for there are 20 ounces of wine altogether, and Q of them are in the wine bottle), so 20-Q of whole is wine, and an ounce of the 20- Q 20

or

20-Q 20

fluid from water bottle will contain

of wine.

20

ounces

tion (in question above) once? It will become (Q1,
Now, how is Q altered by performing the opera-
where-
Q = Q(wine contained in 1 ounce from
wine bottle).

=

+(wine contained in 1 ounce from

water bottle).

20 - Q

20

20

inclose the names of five possible subscribers, with
[22711.]-Nor to waste time with suggestions, I
stamps to cover the cost and postages of the
thousandth number; and, in addition, I inclose the
necessary amount for a dozen copies to distribute
will at once forward to the Editor the name of one or
more possible subscribers, with the necessary stamps come Q', where-
from the office with a subscription form inclosed.
Done in this way, the requisite extra quantity can
for each copy and postage, they can be sent direct
be provided without waste. Will all the subscribers
rise to the occasion, and multiply the circulation?
it him with a vengeance.
the Editor says he likes work, and this should give
I suggested a subscription for a week's holiday; but

in common by that sect among its members who amongst my friends near home. If all the readers Now, do operation a second time and Q' will bewhile not abjuring the practice of ornamental whittling-desire not to restrict themselves thereto Mr. Boord's practical proposal of 9-5 threads to the inch, instead of 10, for our mandrel nose will not please me; but, for the sake of uniformity, I must give way if the majority of our members vote for it. The reflection test" is commending itself to Mr. Boord. This I am glad to see. cheap, and perfect as a test for the surfaces of the It is simple, mandrel; a mandrel that will not bear this test is unfit for our standard.

996.

THE ENGLISH MECHANICS' SOCIETY. is true that many proposals have been made to [22712.]-THE letter in your last issue from found an amateur mechanical society and that "J. M., Ramsgate," is deserving of attention. It hitherto they have led to nothing; but the ruere fact of so many proposals having been made seems to point to the necessity of such a society.

The notion that the standard madrel will increase the cost of our lathe apparatus is contrary to the fact. It will supersede the transfer chucks which are now made for each of the ornamental chucknoses. These transfer chucks figure up to about five guineas in our ornamental-lathe bills. They are complicated, rickety, and spoilable contrivances, devised for the purpose of making a badly-made mandrel-nose exchangeable with foreign chucks. With the slightest injury to the chuck on which they are made they become useless. In a future letter I hope to show the real principle and construction of these transfer chucks; but, just now, have not the time to get the drawings done. For the present I will only add that the transfer chucks I merely do for individual chucks what my mandrel does for all chucks which are properly made. But the roughest and simplest chuck may be used upon my mandrel as well as one fitted with great accu-be arranged. The primary object, I think, of such racy to its cylinder-base and broad face. With the present 9:45 thread mandrel-nose one cannot make a boxwood chuck until one has a special set of lathe nose bit and taps. These figure out in our bills for three guineas, and are useless for other purposes.

As to the fractured Holtzapffel noses, the letters already published in the E. M." give several cases, and I know one that has not yet been published. Whether Mr. Boord's case is an addition to these, I do not know.

The diameter of the mandrel-nose (lin.) cannot safely be lessened unless the tubulation and the exchangeable centres be done away with. The tubulation is an immense convenience. One of our members whose workshop, after mature consideration of our present ornamental tools, has been entirely fitted up by Whitworth and Co., has a larger bore than the 4in., and he finds it a great convenience for slender turning and for other general purposes. But on these points will Mr. Boord favour us by turning up a model embodying his proposals? James Edmunds.

Grafton-street, Bond-street.

= {[( 10 ) *

= Σ 1

=

20] + (10
(유)

9 74-1

9

) + ( 10 ) *

+ +

x 20

( 15 ) " ×

10

+1

ounces

+ &c. +1

which should provide a well-fitted workshop, a And amount of wine left after n times-
chemical, physical, and biological laboratory, and a
In my opinion there is room for an association
library and reading room; which should also par-
members could meet in the evenings to discuss
matters of common interest. I do not think that
take somewhat of the nature of a social club, where
the workshop and laboratories should be open to
members who merely wished to learn the elements
of their craft, although classes of instruction might
practically test original ideas. Many valuable ideas
doubtless remain unproductive, and many re-
an association should be to enable its members to
searches are brought to an untimely end, in the
hands of persons of small means, because some
borrowed. Membership of the proposed association
would prevent this, for under proper restrictions
pieces of necessary apparatus cannot be bought or
the whole instrumental resources of the establish-
ment would be at any member's disposal. Meetings
the officers or other qualified members of the
society of recent discoveries or inventions likely to
might also be arrauged for the demonstration by
interest the members.

sum of n terms of geometric series where 1st

for few members would use the society much. If a
thousand members could be enrolled, half a guinea
The subscription to the society need not be large,
a year would probably pay expenses. Fees would
of course be charged to those members joining
the classes of instruction, and materials would be
charged for in the workshops and laboratories. An
entrance fee of a guinea might be sufficient to pay
the initial expenses.

If any readers of "Ours" should think favoura-
bly of the formation of an association of such a
nature as the one I have sketched, I beg that they
will communicate with me, by letter, at the address
of this proposal to found an “English Mechanics'
Society
given below. If they will do so at once, the result
can be announced in the 1,000th number
Alfred W. Soward.
5, Serjeants Inn, London, E.C.

of the "E.M."

PROBLEM.
[22713.]-SUPPOSE you have a pint of wine and a
pint of water. Take one ounce of each and empty
it into the other, and shake up. There are twenty
ounces in a pint, .., take an ounce out of wine
taken from water bottle into the wine bottle.
bottle and an ounce out of water bottle. Pour
ounce from wine bottle into water bottle, and that

wine bottle after you have done this ten times?
Ques. 1.-How much wine will be left in the
Ques. 2.-How many times must you do it in

an important factor in determining the place of the correctors. A very dense glass could be placed further from the o.g. than a light one, hence requiring a proportionately less diameter. When we say that the larger the o.g., the less the size of the star disc, we refer to the optical image of rays issuing from a luminous point. I should think that it does not appreciably affect the size of the image of a planet under the same power in both instruments.

As regards the plate glass question, I trust "Prismatique" and other practical opticians who may have tried it, will let us have the result of their experience. Do the striae cause so much mischief as to prevent the lens giving a decent star disc?

tion that if a man weighing 100lb. swallows 1lb. repeated merely for the purpose of showing students of brandy he will lie on his back and snore, may be what, unless their brains are addled, they can learn accepted; in fact we may go further, and acknow- and remember just as well from books. Imagine ledge that if a man weighing 2001b. swallowed 2lb., hundreds of dogs being put to the most cruel and or nearly a quart of brandy at once it would pro- agonising torture merely to show over and over bably lead to the collection of the money on his life again the difference between the anterior and insurance policy. Why Dr. Edmunds selects brandy posterior part of the spinal chord, when the in preference to vinegar, mustard, pepper, pickled mere remembrance of the succession of the letters cabbage, Worcester sauce, extract of meat, tea, A M P S, as they stand in the alphabet, for anterior coffee, or Christmas pudding, can only be explained motor, posterior sensory will always enable the by the fact that an aversion to spirituous consola-merest dullard to remember a fact, which, when tion is his fad, and he conveniently ignores the fact learnt, will probably never be of the slightest use that most people are quite as likely to swallow 2lb. to him in his whole professional career. Foreign of mustard as 2lb. of brandy. physiologists are men without remorse or feeling, who delight in torture (there may be here or there exceptions, but I have never neard of them). With In reference to the dialyte mentioned by me in a them, an experiment instead of being a thing to be previous article, I have received the following undertaken when some point of great moment to further particulars: They are in the words of the the human race is in doubt, with regret that they gentleman who made it. "With regard to the may have to inflict pain on a living creature, and plate glass question, the glass was carefully with care that this pain shall be minimised, is a selected,' in the sense that it was picked out from matter that they gloat over, and repeat again and a quantity of pieces at a glass warehouse, so as to again, as they gloated over the horrors of the get a piece as free as possible from obvious imperguillotine in the Revolution. They make experi- fections: but it was not tested in any such way as ments on living creatures their trade, and give Mr. Wassell proposes. In fact, the whole thing themselves up to it, and if there is no need for any was an experiment, the idea being that if, after investigation they try and invent some new experi-working, the plate lens was found unsuitable, as the ment. The agonies of their victims they care no cost was so small the sacrifice of the plate lens was more for than an American for the piece of wood not a serious matter, and a Chances' disc could be he cuts up with his pocket-knife. Your readers substituted for it. The glass was sent to an optician will say that I am nowise too hard on them when with the discs for the correctors to be ground. I tell them that I was informed by Cardinal Manning that an Italian physiologist admitted to him that he was carrying on a series of experiments on dogs. What for? readers will say. To benefit, no doubt, the human race in some way. No; simply to gratify his hellish curiosity by seeing what amount of torture the poor creatures could go through ere the life which God had given them was extinguished.

A man to weigh 1001b. must be an exceedingly small specimen, and, as Dr. Edmunds rightly says, if this man swallows three, four, or five glasses of wine he will be in what is called an afterdinner condition." He will, indeed, Dr. Edmunds, no doubt about it, but he will be easier both in mind and stomach than if he had taken three, four, or five glasses of vinegar or Worcester sauce, both of which the doctor probably uses in moderation. His assertion that a stimulant is that which gets strength out of a man without putting strength in him requires very great qualification. One of the most powerful stimulants known in state of collapse is hot milk. This is a veritable stimulant without the objection he states, therefore all stimulants are not alike; in fact, it is doubtful whether brandy or any spirit can fairly be called a stimulant. The more correct title would perhaps be an alterative.

Dr. Edmunds states, without the slightest attempt at proof, that the difference between the action of a glass of wine and a poisonous dose is one of quantity, not of nature. He is quite unable to see the absurdity of his own reasoning, and that any food, condiment, or medicine can be taken in such quantities as to cause death. If his horse will eat green clover until death ensues, is it therefore a poison, to be prohibited? I was myself a total abstainer for over thirty years, and am not very much different now. A glass of wine in the morning will make me stupid, it certainly does not stimulate me; a glass of wine after dinner will send me to sleep, unless I resist the tendency by a quick walk in the open air; a glass of spirits at night is sometimes a decided comfort, sometimes is quite inert; but in severe cold or ulcerated sore throat I totally discard all physic and take port wine constantly and freely with the best possible effect. It is to me a specific for this complaint, although in health it is one of my greatest abominations.

If rabid teetotalers would not begin by begging the question or making unproved assertions, and building their theories blindly on these, there might be some hope. Surely even the wildest blue ribboner can see the absurdity of Dr. Edmunds's recorded experiment of injecting alcohol to the amount of one-half per cent. of the weight of any animal, and the consequent production of coma. If Dr. Edmunds weighs 2001b, and he injected under his skin half per cent., or llb. of the contents of a rhubarb pie, he would be something worse than comatose; there would be probably an inquest and a verdict of, "Served him right." Temperate, but not Teetotal.

[22715.]-THERE is an account of a lecture by Dr. Edmunds in your last number, from which, as far as I can make out, the sole result of the torturing to death of eight hundred poor dogs is that in the opinion of some. few what most of us call, and shall probably continue to call, the stimulating effect of alcohol, is to be called in future by some other name. This is a good specimen of the justification of the horrors committed by fiends in human form under the name of physiological investigation. If Dr. Edmunds wished to ascertain whether a cup of tea was a wholesome or useful beverage for himself, may I ask him if he would be content to receive his answer from the effect produced by injecting either the very strongest infusion of tea or a solution of theine into his own

veins.

Our profession, I regret to say, is now being taught to depend upon new methods and royal roads to cure, founded on the tortures of the physiologist, instead of being induced to cultivate that common sense which is far more necessary in medical men than in any other class. Where one patient may be benefited by the cruelties inflicted on animals unlike himself, and in which therefore comparisons as to effects of remedies continually mislead, a million would be saved by a better use of all the means we have around us, which common sense, if always at hand, would continually sug

F.R.C.S.

POLARISER FOR THE MICROSCOPE.
[22716.]-HAVING read with interest Mr. Geo. B.
Scott's letter on p. 173, I venture to send you a
little sketch of a polariser I fitted to my microscope
a little while ago, and which is so simple and con-
venient that it may interest those who desire to make
this addition to their microscopes, and who have
not the means at hand to turn out a substage and
fittings of the ordinary kind.

It may be news to some that thin brass tube
(triblet tube) can be obtained of all sizes, so that
tube of one number fits tightly into the next. These
tubes are of the greatest use in instrument fitting.
I obtained a short piece of such size that it would
fit nicely over the tail-piece of the microscope, and
soldered another piece to the middle of it, so as to
make a T. I then made another similar T, the
leg of which fitted stiffly into the leg of the first.
Another small piece carries the Nicol and fits easily

into the cross of the second T. Round this is
soldered a perforated disc of brass with milled edge
for conveniently turning the Nicol. This piece is
painted black on one side with lampblack and
French polish.

The convenience of this fitting is that it need
never be removed from the microscope, but is easily
slewed round out of the way, while, by pulling out
the tube holding the Nicol, it can be used as a
substage to hold an achromatic condenser, &c., the
latter admitting of accurate centring by the four
motions possible to the fitting.

Calculus.

THE DIALYTE AND PLATE GLASS.
[22717.]-IN reply to Mr. Alfred Best, the
correctors are assumed to have a diameter equal to
the width of the cone of light at the place they
occupy, but, practically, they should be somewhat
larger, because it is impossible to tell exactly where
they will have to be placed. and, in addition to
this, the breadth of the image at the focus must be
allowed for. Mr. Best might try contracting the
aperture of the o.g., and see whether any benefit
resulted from it on the completeness of the
corrections. The density of the flint, of course, is

"The idea of using a plate glass disc did not, however, originate with me, for I know I saw it mentioned in one of the several authorities to which I referred. My dialyte was constructed in the main from the directions given in Design and Work some years ago. The radius of the uncorrected o.g. as given there was so evidently too short to produce the ultimate focal length desired that a radius of 30 instead of 20 was adopted with a satisfactory result.

"I regret that I cannot say much about the performance of the telescope on stars; it is four years or more since I made it, and I had it, owing to removal, so short a time after I finished it. To the best of my recollection, however, it gave a fair image when the object was kept in the centre of the field. I consider the dialyte a perfectly practicable construction in the hands of a competent optician, and I believe a future is in store for it, for large instruments more particularly."

I consider this evidence very favourable to the dialyte principle, and I hope if anyone else makes use of plate glass for the o.g. he will test the instrument on the stars and report the result to these columns. We shall then learn whether such glass is or is not fit for optical use. April 28th.

Orderic Vital.

SPECULA TESTING. [22718.]-OUR antipodean querist, Mr. Dobbie (No. 995, p. 151) should study closely the appearauces as shown with his 6in. mirror, both within and without the focus, not only on celestial objects -especially the expanded star disc of 1st and 2nd mag. stars-but those also by an artificial star at the centre of curvature of the mirror.

Now the general figure of his 12in. may be good and true, but if it be "ringed" the definition would be impaired. Next, I would ask, has he ever tried the plan of limiting the aperture of mirror, or of using an "eccentric stop on its face?

In place of the "test bar" we have now in more general use the "Foucault test," as explained to us by the late talented Dr. Henry Draper, of America, whose monograph on the subject has found its way into many amateurs' hands, and will be found extremely interesting. Mr. D. will find it impossible to learn the art of testing without practice and study on his part. I think I would advise, him to proceed first in this way:-Adjust the mirror in its tube as if about to observe a celestial object, making sure that all the adjustments are correct, then remove the "flat mirror" and its support from the tube, thus leaving the tube clear, but with the large mirror in its usual position.

Prepare six blackened cardboard stops or diaphragms, No. 1 to expose the central portion of mirror 2in. in diameter; No. 2 to expose the circular zone or annular ring lin. broad encircling the 2iu. portion previously exposed, and so on, until we reach stop No. 6, which shall expose the marginal inch, or rather cover up the central 10in. Next take a sheet of white paper, and in a circle lin. diameter draw a series of very fine ink lines (black), say one-eighth apart, and cross these at right angles, with a similar series, making the two lines which intersect each other at the centre much thicker than the others-this to more readily find the object in the eyepiece.

On a firm post or bracket fasten this prepared piece of paper, and to the side of the post fasten on the same level the plate carrying the rack focus and sliding tubes which carry the eyepiece, in such a manner that an eye can be directed into the eyepiece, and that the field lens of eyepiece may be the same distance from the mirror as the test object when the mirror is placed fronting them.

Next place the mirror tube horizontal and about