the saddle, as "F. A. M.'s design shows it in
both his figures.

ordinary lathe-bed for the purpose of carrying a
122836.1-A FRONT slideway attached to an
sliding rest has given the best possible results, and
I should ask to have illustrated two beautiful
were it not for the expense which it would entail,
photos. of most elaborate works in ivory and black-
which I have just received from a client in the
wood, executed by a front-slide ornamental rest,
West of England.

such, for instance, as the proposed front-slide lathe.
And unless, when done, it is freely sold, which is
always matter of speculation, the loss is exceed- In a full-sized drawing now before me, I find
ingly heavy; the costly patterns becoming worth- with a total depth 6in. in the bed, I have allowed
less, and the stock unsaleable. Hence the "make 3in. for the open between V edges. So I think
to order" system must, I fear, as a general rule, beF. A. M." will see this allows sufficient for the
accepted, to the serious blood-letting of the in- half-nuts to open so as to clear the screw-threads.
genious amateur.
Major Armstrong's letters appeared in 1881, Nos.
THE LEVER AMERICAN SCROLL CHUCK.-I for Sept. 30th, Oct. 14th and 28th. The discussion,
notice Mr. Hines'
letter, and appreciate it with a second letter from him, appeared, I think,
as of one who knows what he is saying. early in the next year.
Fred Carre.
I must state, however, that I have no
possible interest in the depreciation of the scroll
chuck. I found my own not so reliable as it ought
to be, but did not even publish my own opinion
until it was so fully corroborated by that of others.
I was also led to visit Mr. Churchill, and to gather
other men's opinions privately. A Canadian gen-
tleman wrote me some very interesting and valu-
able letters upon the subject and upon various
other lathe matters, and he told me of a chuck on
the principle of the Oneida drill chuck with direct
screw grip, but, unlike, the latter, with stepped jaws
for large work. It is an Oneida, but not known in
this country. By the bye, I saw a new Oneida
key chuck at Churchill's, of first-class construction
for drills and small bars-a snug, compact, strong
article just introduced. It is the 4in. lever amateur
chuck which I specially alluded to as faulty, not-
withstanding that it is very handy indeed. In this
my opinion has at least found many supporters.
MANDREL WITH HOLLOW CONE FOR SECURING
TRUTH IN CHUCKS.-Ingenious as this device is, I
The slideway attachments which I have made to
do not think it will commend itself to the fancy of amateurs' lathes have been for the purpose of
the readers. No doubt cone fitting tends to self-adding a self-acting arrangement for automatically
centring; but would it not be better to have a coned cutting screw-threads upon various works, either
shoulder behind the chucks, and to hollow these? in metal or ivory and hardwoods, and for accom-
plishing the beautiful spiral or Elizabethan twisted
work in the latter.

The hollow mandrel face looks like a mistake.

I confess I am a believer in mandrels with a plain cylindrical neck, as described by Mr. Hines, with screw not nicked in behind, and a good shoulder turned flat for the chucks to abut against; and I do not think any device will beat this for holding chucks truly and securely. If, however, the cone is at all expedient, it appears to me that' it should be simply carried out as in B2 (Fig. 2). Fig. 3 is the ordinary conical neck extended down to the screw, as in some forms of mandrel, or that the shoulder should have a cone as at C (Fig. 4). As regards the mere serew pitch of a mandrel, I do not think it deserves quite all the attention it has of late received, for although it were perhaps impossible to devise a better mandrel than that of the learned doctor, I doubt if it would enable ornamental chucks to be transferred and yet run true; and if this is not attained, the universal mandrel Ecrew thread does not appear to be a necessity. O. J. L.

THE FRONT-SLIDE LATHE.

[22835.]-F. A. M." desires to know how my suggestion of clamping the sole of the rest to the back side of the bed-top could be carried out. I may say, the thought in my mind at time of writing was a detachable piece, planed with a V, to fit the back edge of lathe-top. This piece would have a boss on top, on which, or in a hole in which, the back-stay might be fixed. This piece would be bolted to end of the sole of slide, and, of course, would have to be removed when it was needed to shift the saddle to back of the poppet. It is only intended for use when large discs require to be turned; but I do not put this forward as anything more than a suggestion, or as by any means the only or the best way such a thing might be done. When we get as far as the slide-rest and saddle, I have no doubt some one, if not I myself, will have been able to give the point more consideration than I have as yet.

I did not say that such a slide was useless if cast solid upon the lathe-bed; but in view of the fact well known to mechanical experts-that durability of machinery is chiefly dependent upen extended pointed out the desirability of retaining the modern surfaces, where they slide one upon another-I English form of lathe-bed for great pressure and heavy work which appeared to be in prospect for the lathe under discussion, by the request made to have it with a gap bed.

a

To a lathe already fitted with a large number of
chucks and accessories, which has not only be-
come valuable to its owner on account of the
amount which has been spent upon it from time to
time, but from its handiness and convenience
through long usage, such an additional advantage as
front slideway affords can hardly be over-rated,
and I have overwhelming testimony to the thorough
satisfaction which these rests have afforded.
There is no doubt that a lathe-bed with a frontslide-
way can be produced to meet the general requirements
of amateurs who find their most enjoyable recrea-
tion in doing various kinds of mechanical work:
and one with its whole construction such as to make
it an automatic and general operator, which would
fairly stand the test of usage and time; and, with
the best half of a lifetime spent in designing
machine tools, I would say there is no difficulty
whatever in either designing or constructing such
an apparatus.

I have forwarded all my standard lathe-hobs-
those of my uncle Cawdron and my own standards,
tabulate their details for publication in the
to Dr. Edmunds, who has kindly promised to
ENGLISH MECHANIC. The advantages of intro-
ducing a defined thread-form and aliquot rates for
the ornamental lathe

can hardly be

over

estimated.
Griffin Works, Norwich. Edward Hines.

the hand or slide-rest. The real working strain
due to turning is all taken by the front shear. Even
in a bed with connecting ribs, only part of the
working strain is thrown on to the back bearer, and
it is only in the box form that the strains would be
at all equally distributed. I mention these points
only to show that a single web properly stayed will
do the work quite as well as two only partially
connected. "J. H." is wrong about the planing
of my bed as shown in drawings of 7in. lathe. If
he examines the elevation, he will see that at the
base of headstock a shallow recess in. by in. is
cast for the very purpose of ending the cut, and the
individual bed in question was (so the firm for
whom I designed it informed me by letter, in answer
&c.), "rabotté d'emblé "-i.e., planed at one set-
to my instructions as to planing, boring, fitting,
ting. As to the boring of headstock, that and
ting with a special boring bar, nearly the length of
cylinder of poppet head were also done at one set-
the lathe bed, steadied of course where required. I
have just had, through the kindness of one of our
contributors, a good study of Northcote's "Lathe
in my idea of driving leading screw from a back
and Turning," and find that he has anticipated me
shaft, with a double set of radial arms and
wheels; but he also in his "Multipurpose
Lathe " had the mandrel head cast solid
no difficulty in
with bed, and yet found
twice setting of bed on planing machines would,
the boring. "J. H.'s" remarks about the
however, apply to all gap beds, as it would be im-
possible otherwise (unless the table, like one or
two American tools for circular planing, revolved,
or was capable of being set at any angle in the
the gap. I have, from the same source, been
same plane with reference to travel) to plane out
favoured with a view of a photo of one of Messrs.
Cooke's F.S. lathes, and I particularly notice that
they have adopted the very form of slide I and also
many of our correspondents advocate, but without
the (to my mind) unnecessary overhang of bed.
Now, as Cooke and Co. may be taken as excellent
authorities in medium sized lathe construction, I am
course of next week, to be able to send you a draw-
pleased to find myself so supported. I hope, in the
ing to scale of my proposed bed for a 4in.
S.A.F.S.L. with 4in. gap, thus admitting a dia-
meter of 16in., and to take 3ft. clear between
centres. Now, as with this diameter and leverage
there will necessarily be considerable torsional
strain, and as this takes place mostly at the gap, I
have therefore departed considerably from the
bed at both ends to standards or to a bench. In
usual mode of construction-viz., of fixing the
a gap bed the angles immediately at the bottom of
gap are the weakest part; and in any such bed,
supported at each end and loaded at or about the
gap, there will be considerable defection more or
less according to the load, and this increases directly
depth of cut, the material and its configuration. To
as the leverage or radius of work in the lathe, the
obviate this, I prolong the gap framing sufficient to
form a wide based foot or standard, the left-hand

end of which forms a stiff cantilever, on which is
cast or bolted, as the case may be, the headstock.
As I intend this lathe to do (for its size) compara-
tively heavy work, I propose to take all heavy
torsional strain off the mandrel, and turn all work
over 9in. or 10in. from a geared face-plate, the
same as in shop surface or wheel lathes; of course,
this will make the bed heavier than it would have
been under ordinary conditions; but it will, I think,
make a satisfactory job.

There is some good in S. Austel's design, and next week I will send a tracing of his to fit, with suggested alterations. I don't understand his screw clutch action at all. Is the half-nut to work in and out by a long pitched screw on handles, or how? Our friend O. V." has not appeared in 66 ours for the last two numbers. I miss his letters and "F. A. M.'s.” Mechanicus.

THE FRONT SLIDE LATHE-IS IT

[22837.]-I QUITE agree with F. Carre in his observations relative to the above. We do not propose a new lathe; but, as F. C. says, a new bed, fitted to receive various attachments to suit the class of work to be done; and I contend that it, the F.S.L., will do sliding and screw-cutting quite as well as the present usual lathes. The bearing surfaces are not as large, it is true; but they are not so much exposed, especially the vertical faces, to dirt and grit as the present horizontal ones, and not at all more so than any shaping machine with fixed The back-stay I have not yet got settled to my ram head and travelling work bracket, as I have satisfaction; at present I see no better way than as mentioned in previous letters. The particular form I have above suggested. Here "F. A. M." has fresh of bed remains yet to be decided on; of course, I ground to break on. But that he is the first and prefer my own, and I notice that "J. H." and only one who has proposed that the top of the bed others endorse my view as to the arrangement of in the front-slide lathe should bear its share of the top race-i.e., flat at back and Vee, truncated, DESIRABLE ?-OUR 1,000 ISSUES. pressure from cut, is not in accordance with the sloping forward; the inside Vees I object to in any [22838.]-I FEAR I have scarcely made my facts, as the following references will prove. In form, for reasons I gave some time ago. In the meaning quite plain to Mr. Fredk. Carre, and with the first letter I wrote on the subject, Jan. 11th, section "J. H." sends us this week, I notice that your permission will endeavour to do so from his p. 410, last but one paragraph, where the germ of he also covers the top of his saddle bracket by a own standpoint-i.e., regarding the amateur's lathe what he claims as solely his is clearly stated by me. projection of the bed. I cannot imagine that a as a general servant of all work. Now, Sir, I do Again, Feb. 15th, p. 516, "The rest might be made practical man would do this, otherwise than in de-a little of most things, and therefore use my lathe to slide forward on to top of bed, between V slots ference to a (I think) mistaken idea of some of our for turning, &c., wood, brass, iron, and steel. on top of bracket." March 7th, p. 14, "Some correspondents, about turnings and dirt accumu. With it I require to drill and bore holes of all sizes of the strain in cutting would be borne by lating in the top groove; even supposing they did, in metal, &c., to cut screws and gears, or cogtop of bed, for I intended the base of the slide-rest it is quite as easy to clean out as off an ordinary wheels, to flute taps and rimers, and, in fact, to do to be capable of being slid on to top of bed, before any odd jobs that present themselves from fitting being bolted in place on bracket." This was all up a telescope (I am now at work on a 5ft. focus written before "F. A. M." appeared on the scene. 3in. achromatic), or a photographic lens mounting As to his right to call my bed a "paper bed," it and camera, to making a bicycle or a 2-horse really does not matter or concern me in the least; engine, &c., and, in addition, I want to make my his challenge will be answered all in good time. lathe do my planing, shaping, and slotting; the Meanwhile he must be satisfied with what I have latter I do with a slotting tool in the ordinary tool stated, that "there is room for the rest." If more post, the wheel or work to be done on the faceroom is needed, it is to be obtained in the way I plate, the mandrel locked fast, and the “traverse have already stated, adding in. to depth of the obtained from the leading screw by pulleys on it bed, and not in the way F. A. M." has gone and the driving shaft. The planing and shaping is about it. For there is no need, and certainly no all done by milling cutters, the work being fastened advantage, in having the rest so far from its seat in on the cross slide, to do which it is obviously

bed, and with the advantage that the surfaces being
either vertical or bevelled at an angle of about 40°,
the chips have no great tendency to stick there. By
following this idea, so much valuable depth of bed,
representing leverage, is lost, while the top tables
of bed (which in the F.S.L. do little more than
support the heads) are made of unnecessary width.
Again, why has "J. H." made his back shear or
bearer thicker than the front one, which has to take
most of the strain? In the double shear cast-iron
bed of an ordinary foot lathe, the back shear really
only serves as a distance piece to guide the poppet
head, and as a strut for clamping down both it and

ENGLISH MECHANIC AND WORLD OF SCIENCE: No. 1,002.

necessary to have plenty of room under the centres
and a long cross slide, which latter is not possible
(practically) with a
tion to it. My plan is to have a "bed" of extra
"front slide," hence my objec-
strength (strong enough in fact for a 9in. centre),
and fit upon it a pair of 5in. headstocks raised on
strong hollow "boxes" to 9in. or more, to fit the
saddle with a long cross slide (nearly 2ft.) with a
vertical slide under it, and use tool posts and rests,
as previously described, and I still prefer this, not-
withstanding all that has been written on the
"front slide,"-
was given by our old friend "O. J. L." a long time
-a good design for which, by the bye,

since.

I do not agree with Dr. Edmunds (letter 22812) as to reducing the friction by shortening the length of the "collar bearing." I have tried both plans, and find practically, apart from theory (which I believe confirms it), that the friction (that is the actual power expended) varies directly as the pressure and speed of surfaces in contact, and is not affected, within reasonable limits, by the amount of surface in contact; hence friction is reduced by reducing the diameter of a bearing, but not by its length, while on the other hand reducing its length, increases the wear with no compensating advantage in saving of power. This is a point that might, with advantage to many, be thrashed out in your columns, and if I am wrong I need not, I think, say that I shall be glad to be corrected, as, on all points, I desire to learn, before anything else, and I am always open to conviction. All I ask is to be shown the man that can convince me, like the "backwoods" American lady when she held the shooting iron."

66

May I be permitted to say that our much esteemed confréres, "F.R.A.S." and G. Calver's observations, anent your 1,000 issues, give my sentiments exactly. I have been a reader of ours 27 from its birth, but only an occasional contributor, adopting the plan of "giving from my store" only when, so far as I could judge, others had not precisely the same article at command, or I had some well-ascertained fact, and thus saving space. Previous to "ours 99 memory serves me correctly, the Mechanics' MagaI used to read, if ine and the Practical Mechanics' Journal, but neither satisfied my appetite nearly so well.

Finem Respice.

LATHE MATTERS. [22839.]-"H. E. R." has done us good service by calling attention to the practice of the American

lathe makers.

"Faber" (on p. 191) proposed the "tail tube," which would, doubtless, cause less friction than the ordinary washers, though more than the usual tail pin. Čan "H. E. R." this" tail-tube," give us a section of readers help us with information as to the conor will not some of our American struction of their lathes? I should much like to see working drawings of the "Cornell" lathe, of which a notice appeared not long ago, and to know how the "shell chucks are made in which work can be clamped and released without stopping. Dr. Edmunds deserves our thanks for his description of the Cooke lathe. I see both he and "Electric Lamp" think we cannot improve upon that section, Dr. E. suggesting that the torsional strain is better met by the double-shear pattern, whilst "F. C." says the girder section resists both strains best. In this I think him right, and without going into calculations, I think Dr. E. and "Brockley will be convinced if they will nail together some strips of in. wood so as to make a long open frame, say, 3in. deep by 3in. wide by 3ft. long. Now, let them take one end in each hand and consider whether that is a good shape to resist torsional strain, and whether all the strain must not come on the four small corners. represents the double bearer lathe-bed when the This long frame fairly bolts pass through to the bottom flange, and there are no cross webs.

Now take the frame to pieces, saw one long piece down the middle, and nail each half on the top and bottom edge of the other so as to form an I or girder section, and when you again take one end in each hand you will find you have a bar of more than double the torsional strength of the other. Probably neither of these sections will resist the twist caused by setting the lathe on an uneven foundation, and that caused by turning must be so insignificant that we need only provide against vibration: that experience alone can decide, all calculations being delusive.

Once more I must venture to differ from our friend he says (p. 282, bottom of first column), "The friction in the front collar depends upon the area in contact with the collar, and by shortening the collar in which the neck runs, the friction can be cut down at pleasure." Now I was always taught that increasing the bearing surfaces increased their duration without augmenting the friction. On consulting Abel's "Rudimentary Principles of Machinery," I find (page 51):

1. "Resistance of friction is dependent on the

nature of the substances.

IV. "Resistance is independent of the amount of

surface in contact as long as the same is large
enough to prevent heating, &c.

the rubbing parts as long as no abrasion takes
V. Resistance is independent of the velocity of
place.

pressure (no abrasion taking place).'
VI. "Resistance is in direct proportion to the

seems to prove that a 6in. mandrel will require no
Rule V. requires a word of explanation, as it
have noticed that other correspondents have been
more power to turn it than a lin. one, and as I
on the Steam Engine" (page 63):-
misled in this way, I quote again from "Bourne

the rubbing body if the friction over a given amount
of surface be considered; but it increases as the
"Friction does not increase with the velocity of
velocity, if the comparison be made with the time
during which the friction acts."

require the same amount of force to cause it to
turn once, whether that revolution be made quickly
Thus, Rule V. shows that the lin. mandrel will
or slowly. If it make two revolutions (whether in
the same time or not), that will take twice the
force. The 6in. mandrel will take six times the
force to cause it to revolve (irrespective of the
time), because the sliding surfaces move over six
times the distance.

with a foot-lathe, and wish it to run easily at a
speed of 8 to 1 suitable for wood, you must have
I conclude, therefore, that if you are dealing
perfectly-formed and polished necks of a small
diameter. Their length has nothing to do with the
friction, except that if you make it very short the
pressure may reach 800lb. per sq. in., when the oil
Nor should you have them of an exaggerated
would be forced out and the surfaces destroyed.
length, because then there will be a slight increase
of friction owing to the viscidity of the needlessly
large layer of oil.

have a 2in, mandrel neck or more; but if you have
to drive by the foot at a speed proper for wood, do
If, then, you have power at hand, by all means
not have a neck of more than lin. or 1in, unless
you are used to the treadmill! A lin. neck should
diameter, and that is why I do not much care about
not be expected to do good metal work on a large
a gap for a foot lathe, except for platters of wood
or iron, with arms or projections, &c.
F. A. M.

"E. M." about the American scroll chucks, and I
AMERICAN SCROLL CHUCKS.
[22840.]-I HAVE seen many letters in the
of Messrs. Churchill a three-inch scroll chuck,
am, although late, tempted to add my experience
which I believe is one of Cushman's, although it
to that of others. About eight years ago I bought
does not bear their name.
£2 178.-but it is as good now as when I bought it,
not, it has proved a first-rate chuck. It cost about
Whether it is theirs or
and I have never regretted the purchase. It does
not hold work perfectly true, but nearly so, and I
find it of immense use for drilling and boring. I
think it is much to be regretted that the Yankees,
as they do; it is, as I believe, a thorough mistake.
I have seen a lot of cheap American chucks which
and also the English, go in for cutting down prices
I only needed to look at to see that they were
simply rubbish; but it is the old story-if you want
a good chuck you must pay a fair price. But that
which chiefly led me to write this is to caution any
would-be buyers against a form of chuck with
several steps thus-

This looks very ingenious as taking three sizes, but
practically that part of the jaws taking the larger
diameter is so much in the way of the smaller, that
myself a chuck with only one step, almost like
the smaller are almost useless. I prefer very much
the letter L.

my own runs from lin. to 0; but then it does the
work as nearly to perfection as may be, and that is
This form has a rather limited range; for instance
after eight years' wear. Another reason for my
writing is that I hit upon a most simple, but I think
a most useful, contrivance. Every turner is aware
the closer you keep the work to the collar of the
mandrel the better. But if you hold a small piece
that in turning anything held by the mandrel only,
of wire, say in. diameter, in one of the American
chucks, and turn very close to the jaws, there is the
great risk of the tool slipping, and catching the
Now the plan I have adopted is to take a disc of
metal-a bronze penny will do very well for small
chuck and, perhaps, causing serious damage to it.
diameters-drill a lin. hole as near the centre as
you can, and slip it on to the in. rod you are
turning. It is clear then that you can turn close
up to the chuck without the risk of doing any mis-
chief. In fact, the disc of metal may often be very
useful as a gauge.

JUNE 6, 1884.

DOTTING PEN, cleanly. With the usual construction of pen, all [22842.]-YOUR correspondent "A Fellow of the draughtsmen find the same difficulty, but make a culty in getting an ordinary dotting pen to work Royal Astronomical Society" (p. 252) finds a diffi practice of trying the pen on a piece of spare paper by supplying the ink from a camel-hair brush contrivance which lessens the liability to smudge until it works correctly. I inclose a sketch of a

fitted in the interior of the pen, and which removes
for replenishing with ink. This pen I bought many
years since of M. Baraban in Paris, but I do not
know if any English maker supplies a similar in-
strument.
R. Inwards.

SPEED OF EXPRESS TRAINS. to speed :[22843.]-THE following is a list of the fastest expresses on the London lines, arranged according

Great

Western

gauge).
Great Western

(broad (narrow

and

431 58

Dover

Midland
Great Northern
gauge).
London and North-Western
Great Eastern
London, Chatham,
London and South Eastern..
London, Brighton, and South
London and South Western.
Coast

55 47 115

46

1 5

461

130

45!

50
69
471 1 3

in the E. M." of last week, I beg to state that I
am unable to elucidate completely the assertion
HIGH SPEEDS-LOCOMOTIVES.
brought forward in the article of the Engineer's
[22844.1-IN reply to "Nun. Dor.'s" letter (22773)
ment of petroleum in fireboxes of fast-running
number for May 16th, with respect to the employ

locomotives.

about this. It is true that the amount of units of heat generated by the combustion of one kilogram of petroleum, or other similar mineral oils, is about There ought to be a little more explanation 12,000; but then I have not the least idea how this solves the problem-all the more that we have in when they do not give out so much heat. In my opinion a properly selected coal will always be England plenty of good coals that will do very well cheaper than petroleum. Trials were made in France some years ago to ascertain the value of petroleum as a locomotive fuel. The result showed for this reason it was abandoned. that, after all, this material is dearer than coal, and

heating surface. This state of things cannot be altered as long as the present arrangement is kept. I think that English engines have too little ing 120 kilometers an hour is, of course, restricted to lines which have not gradients of more than gor The use of engines, running with a speed exceedTHE ENGLISH MECHANICS' SOCIETY. locomotive's tractive force decreases rapidly with or only short ones of, which the vis viva of the train could easily overcome. The efficiency of a under this heading in your issue of the 9th ult., Iceeds much 401b. The use of [22841.]-ADVERTING to my letter (No. 22712) the steepness of the incline. At the above speeds the resistance per ton ex“singles” is not

C. A. T.

of the inner circumference on the body of the planet. There is across the white equatorial band on the body of the planet, a very narrow dark belt close to the edge of the dusky ring."

The

In regard to the query of "A. S. L." in regard to the front view telescope (p. 237), I may mention, that many years ago, I witnessed on one occasion the performance of such an instrument. mirror was of speculum metal, of inferior quality and polish, with a diameter of 8in. The eyepiece was directed to this mirror. I still remember the fine image it gave of Jupiter, which I have never since seen surpassed with regard to the vivid distinctness with which the belts were shown. Those present were taken by surprise at one circumstance, viz.that one of the satellites appeared to be square, and not round, as we expected to have seen

it. None of us could then explain the cause of Computed for the winter months: for the summer months the corrections must be slightly diminished. this appearance. We know the explanation now, for it is given by the Rev. Mr. Webb in his "Celestial Objects" p. 168, 4th Ed. That such an appear.

Jan.

Anti-Lunar Tide.

Feb. Mar. Apr. May. June.

anti-lunar declination.

ance should have forced itself on those who did not TABLE VIA.-Showing the Correction for Lunar or | TABLE VIII.-Showing the correction for lunar or expect to see it, shows, I think, that this form of telescope may have considerable defining power; and as to its superiority in light there can be no question. The objection to it is that to perform well, it requires to be of long focus. The mirror in question had a focus of 8ft. It may perhaps be reserved for Mr. Wassell to add one more to his many previous triumphs of ingenuity in speculum construction by devising a mode of obtaining a form of reflecting surface, which with one reflection would combine good definition with a manageable focus. I hope he will turn his attention to this, which, if it be a possibility, would be, perhaps, the greatest advance that now remains to be made in the construction of the reflecting telescope. James Dunlop.

Bonnington-bridge, Edinburgh.

Moon's
Trans.

Lun.

Anti.

Lun.

Anti.

Lun.

Anti.

+ Lun.

+ Lun.

Anti.

Lun.

Anti.

B.

h. in. in in. in. in. in. in. in. in. in. in. in.
0+5 +0 +5 +1+6 +2 +6 +2 +4 +1 +3 0
3 5 1 5

6 6

3

110222

4+1

4 2

+1 2-2 2 5+1

4-1 4
5+1

15 6 3 6

18 5 2 4 0

21+4+0+5 +0 +5 +1 +5 +1

5+1

5+2

3-1

-1

SCIENTIFIC DIALOGUES ON THE

TIDES.-VII.

[22848.]-Q. IN the matter of the actual computation of tides, it perhaps would increase the interest which is taken in the subject if you give an epitome of the method by which numerical results are obtained.

A. In order to do this, it will be necessary to give you a few of the tables which have been devised for the purpose, together with some instructions as to the method of using them. But, pray remember that those which follow are in a very abridged form, and that the tables actually used are much more extensive and elaborate, adapting themselves, in fact, to all positions of the moon and sun. Still, by carefully using these abridged tables good approximate results may be obtained, which will be capable at once of verification. I begin with the

Moon's

B.

July. Aug. Sept. Oct.

Anti.

h. in. in. in. in. in. in. in. in. in. in. in. iz.
0+4 +1 +5 +2+7 +3 +6 +2 +3 +1+3+1
4+2 4+1 5 1 4 0 3 1
3-1 3-2

3

5 2

+1

6

0 5

tables relating to the height of the tide, as these are TABLE VII.-Showing the correction for the Moon's

B.

B.

h. m.

16 0

4 30

122 0

21 8

10 30

25 4

With the parallax ranging from 53' to 57, the increments must be decreased by an inch; with the parallax ranging from 57' to 61', the increments must be increased by an inch. Changes in the inclination of moon's orbit require separate tables. Q. The next thing is to work out one example of the use of these tables. Suppose we take the morning tide of June 1st, 1884, at Liverpool?

A. Very well: I will give you a form of compu tation duly filled up.

Greenwich apparent time of

will not show your breath. Doctors and dentists can use it on small glasses with which they examine the teeth and throat, and will not have to wipe them off at all. Surveyors can use it on their instruments in foggy weather, and there is no film to obstruct the sight. In fact, it can be used any10+ where to prevent moisture from forming on anything. It does not injure the usefulness of fieldglasses, &c.; in fact, a small drop of pure glycerine 4+ in a small hole in a sheet of brass makes a good lens for a small microscope. I first saw this used on a steam-gauge glass on a Sound steamer where the gauge leaked inside." E. A. M.