in the case of letterpress work. Rough calf is finished with black lines. A sponge is tied upon the end of a small stick and the sponge dipped into "iron liquor"; the sponge is laid upon the edge of the roll while the stick is held in the hand close against the handle of the roll while the roll is running; the sponge keeps it supplied with the black fluid, and the result is that the lines upon the book are black. The titles are made upon red leather in gold letters and ornaments. The description for this was given in Letterpress Finishing.

Most ledgers and many other books have indices accompanying them; sometimes they are bound in the front of the book, and very often they are separate; but whatever they may be they are always cut in the following manner, unless wanted specially cut for some definite purpose. An index consists of a book of 24 leaves-i.e., a "leaf for a letter." The book is divided into 24 equal parts. In ordinary practice we keep a scale for this purpose. To make the scale we cut a sheet of paper, and cut it the shape of Fig. 56, making one edge about 12in. and the other about 20in. We then divide each edge into 24, and draw lines from point to point. We have by this means a gauge that will do any book from a foolscap to a super-royal. This is placed in the book, and the first leaf is lifted up with the finger and thumb of the left hand, and a small cut is made in it about in. or more from the edge, keeping the scissors on the pencil mark, SO as to cut in the right place. The second leaf is fitted and cut at the second mark, the third, and SO on until the whole of the leaves are cut. A strip of tin is now placed in these cuts, taking care that it enters every cut until the bottom. A straight edge is now placed upon the edge as far back as desired, and with a knife the pieces are cut away. This leaves the little steps upon which the letters are stamped with black or red ink as taste may dictate. Fig. 57 is an exaggerated sketch of a few leaves, and shows the part cut with the knife and the part left below the tin and consequently in the book.

is a demand for so-called self-propelled vehicles
capable of carrying from two to four persons,
and whether steam or electricity is used, the
mere question of expense is a small matter to
those who would purchase. But it may be
doubted whether, the Legislature permitting,
vehicles of the kind would have a long life on
the ordinary conntry roads running at speeds of
eight to ten miles an hour. It is certain that,
whatever motive power is applied, it cannot
drive direct on the wheels, but must be connected
to them by a chain or band, so that the engine
and other parts having a rectilinear motion will
not be disturbed by the inequalities of the road;
and yet a great part of the weight must be on
the driving-wheels in order to get sufficient
adhesion for advancing. Whether any modern
appliances can beat those introduced early in the
century remains to be seen; but it should be
remembered that the great difficulty is not
in the machine itself, nor in the means
adopted to work it, but in the state of the
road. With a smooth travelling - bed, any
machine can run along easily enough with the
minimum of wear and tear, provided the power
is applied through a flexible link; but if the
link is as practically rigid as it is in a locomotive
motive-power vehicles will soon come to grief
unless they run on rails or smooth surfaces. As
to the source of the power, that must depend on
circumstances, and on the likes or dislikes of the
rider of the vehicle. Storage batteries would be
convenient, if expensive; steam or hydrocarbon
engines would be troublesome if economical; but
they sum up the list of available motive powers,
for springs are altogether out of the question, and
no one proposes to use compressed air. If, how
ever, the Legislature could be induced to relax the
stringency of the present Act, and allow vehicles
weighing, say, not more than an ordinary loaded
omnibus, to travel by any means at a rate not
exceeding eight miles an hour in towns and 20
miles on country roads, we might see the de-
velopment of some ideas which have long been
kept in the background owing to the existing
state of the law.

borne out by observation during many years, and
under greatly varying conditions of its production.
Let an attempt be made to separate any part of
a circuit in which the current is maintained by a
sufficient E.M.F. or potential, and we find that if
flash or spark of varying length, which becomes a
the separated ends are moved quickly we get a
flame of great heating effect if the current be of
large rate of flow. If the separation of the two
parts of the circuit be made slowly, a continuous
flame or discharge will take place between the ends
if they be not too widely separated, or so widely
separated that the potential or pressure of the
current is not sufficient to force current across the
space. With considerable potentials and heavy
bridged. Whether the separated ends be of iron,
currents a space of many inches may thus be
copper, platinum, zinc, or other conductor, the
hot discharge is still formed. Therefore, while
the electric arc is generally spoken of as that flux
occurring between carbon ends separated, of
course it cannot be so limited, and we frequently,
therefore, refer to copper arcs, iron arcs, carbon
arcs, to distinguish one from the other. What,
then, is the arc so formed? Is it heated air
between the ends separated containing detached
particles of the conductor in process of carriage, as
case? No; the arc proper is composed of a stream
was apparently thought for a long time to be the
of vapour arising from the actual boiling or
vaporisation of the solid or fused ends of the
separated conductors. In so far as the surrounding
air mixes or combines with this vapour stream, it is
modified by the presence of oxygen and nitrogen;
but the air, or any other gas, is not essential to be
present, and is merely incidental to the formation
of the true arc stream in air. Indeed, it may seem
strange to some to speak of vapour of carbon,
copper, iron, platinum, &c., but their production is
the electric arc there is a real distillation of the
merely a question of temperature in any case. In
conductors forming it, and this accounts for the
variation of colour and temperature to be found in
different arcs. The copper arc evolves a peculiar
green light, which is exceeding trying to the
eyes, as those who have experienced its effects well
know. Zinc gives a whitish blue, while the carbon
arc proper is purplish in tint. The arcs from various
metals give, in the spectroscope, the characteristic
lines of the vapour of each metal.

As a curious incident, showing the presence of the metal vapour in the arc, I may mention the fact that when by accident a person has had a portion of

As I have been asked for addresses where amateurs may buy tools and materials for THE NATURE OF THE ELECTRIC his clothing bathed for an instant in a heavy copper

bookbinding, I mention Messrs. Berry and Roberts, 21, St. Bride-street, London, E. C. This firm keeps all classes of material, tools, and appliances.

MOTIVE-POWER CARRIAGES.

ALTHOUGH we cannot agree with, La Nature

ARC.

By Prof. ELIHU THOMSON.

arc caused by a short-circuit of heavy current mains there has been found a considerable deposit of copper, enough, in some cases, to give the reddish colour of copper to the surface bathed, which, if moistened, turns green by oxidation. It also gives a deep blue to dilute ammonia in which it is washed, thus showing the presence of copper. In like manner these metallic arcs will give a deposit

representing it. But these views are remarkable of the metal on cold surfaces which they toucht

face to face."

66

IN the course of a paper read at the Electric Light Convention recently held at Providence, R.I., Prof. E. Thomson said:-In regard to the idea put forward as to the nature of the electric arc there is even a wider divergence than in the figures used for that an "important problem" is solved for their general inaccuracy or crudity, and It appears to be the positive pole which gives out by the experiments made with M. Serpollet's evidently have been handed down with modi- the vapour stream. With carbon the positive steam-carriage in Paris (p. 48), there is no doubt fications. Few of those who have written about vaporises steadily, and is consumed much faster that a large number of people are anxious to the electric arc, at least in the textbooks, seem than the negative. In the use of the arc, however, possess a vehicle by which they can traverse the to have had the courage to look at the arc, or they for lighting, we have learned to distinguish between roads without more than the minimum of may have seen it through a glass darkly and not what is called a "short-arc" and a long-are" muscular exertion-such exertion being confined It would require too many and system. In short-arc systems the carbons are to steering the vehicle and regulating the pro- most of them the light of the arc is attributed to systems. Let us suppose the case of two carbons lengthy quotations to give these various views. In burned much nearer together than in the long-an pelling machinery. M. Serpollet's device, it intensely heated carbon particles transported by the touching each other with a current passing, and appears, steers clear of the objections to smoke current from one pole to the other. In most of then that we very slowly separate them, stopping and noise, and as it can travel at a speed them the idea of carbon vapour as a possible factor to observe effects. When the contact is light, quite sufficient to suit the desires of most of never seems to have arisen. Others attribute the before actual separation a visible heating of the those who wish to dispense with horse traction arc to the heated air between the carbons which meeting ends is seen. On attaining a small sepa or muscular power, it may ultimately become a carries carbon particles, some of which are burned. ration the space between seems filled with hot successful steam-carriage from the economical, as The following quotation from a book on electric vapour, and we have a short arc where the separawell as the practical, point of view. At present lighting, published in 1884, is a type of many such tion is perhaps not over two to three one-hundredths the Act of Parliament blocks the way for a really the resistance which converts the current into heat of carbon from the flattened end of the positive accounts: "In arc lamps, as we have already stated, of an inch. There is also noted an active transfer practical test of the value of the device; for four is that of the heated air between the ends of two and a deposition of carbon on the end of the nega miles an hour, and a boy or man in front with a carbon rods, from one to the other of which the tive carbon. This deposited carbon takes the form red flag, are not exactly the conditions under current passes. The light is produced by the incan- of a mushroom end after a time, and breaks off. which enthusiasts in this direction care to work. descence of the ends of the carbon poles, and of the Meanwhile combustion goes on at both poles, and The law, as is well known, was made in connec-minute particles of carbon which become detached wears away the sides of the positive carbon while the tion with heavy traction engines, which certainly and float in the heated air between them. The transfer of carbon wears away its tip or crater. The could not be tolerated running at anything much heated air containing the particles of carbon forms burning also wears away the negative at the sides, over the pace of an ordinary waggon; but it is what is called the electric arc." Here the heated while the tip is built up by the mushroom deposit from argued that light vehicles, no matter by what air and carbon particles floating therein are the arc. But the cutting in of the negative finally power propelled or drawn, ought to be exempt Nothing is said of carbon vapour having anything both carbons are eventually consumed. To develop electric arc." definitely stated to form the severs the mushroom tip, ard it falls away. from the legislative restrictions. So far as the to do with it. public are concerned, there is no more reason for tive carbon burns twice as fast as the negative is potential that is needed for a long arc, or about 25 Even the statement that the posi- a short arc there is required a little over half the prohibiting a tricycle or a carriage from running very frequently found unqualified in any way what- volts more or less; and therefore, to give out equal about at eight miles an hour, say, than there is ever. The experience of the lamp-trimmer is, I heat energy in the arc, the current must be doubled for limiting the speed of a Hansom cab or a Pick-need scarcely say, not in accordance therewith, the in the short arc over what it would be in the long ford's van, and it probably only requires the fact being that the rate of consumption, even in arc. The short arc is subject to the objection of a concerted action of those who desire to be free in direct-current arcs with the same size carbon in continual frying sound emitted and great variations the use of motive-power vehicles to obtain a both holders, varies sometimes quite widely from of luminosity. It requires a very dense and hard modification, if not a repeal, of the Act which the proportion stated. However, we shall make carbon to conduct the current without great loss, at present practically puts a stopper on the and involves line loss of at least four times the use of steam and electrically driven vehicles. M. amount with the long arc if equal gauge wires be Serpollet's steam-carriage can be seen at Messrs. used. Bryan Donkin and Son's works in Bermondsey, where M. J. Pierson has located it for inspection while introducing it in this country. There

better progress if we discard at once the older
notions, and, adhering only to that modicum of
the error by the results of our own observa-
truth which often accompanies error, supplant
tions and experiments. My endeavour will,
therefore, be to state as briefly as I can such
views of the nature of the electric arc as seem to be

Hence

In fact, while in the past such arcs were common, their number is diminishing, as they are being replaced by the more efficient and completely developed arcs called "long arcs," which are so

FIG. 1.

called to distinguish them from the "short arcs.' carbon into liquid carbon at arc temperature under | The motor weighs 1051b. Its speed is 10,000 revoReturning to our separating carbons we find that as a high pressure of inert gas. No one has as yet lutions per minute. The power developed by a the space or arc is lengthened from the short-arc seen carbon in this liquid condition, and the electric boiler pressure of 1001b. to the square inch is condition we pass a stage of great flickering and arc alone has made us acquainted with carbon 25H.P.; but the motor is abundantly strong to unsteadiness and a fluctuating potential between vapour. One cannot fail to be impressed with the bear a working pressure of 150lb., at which pressure the carbons, and then reach the stage of fact that the conveyance of carbon in the arc has a about 40H.P. is developed. production of the long or quiet arc. With striking resemblance to a plating process where 10 amperes the separation may now be about metal is taken up by the bath from the positive in. to in. or more. Smaller currents plate and deposited on the negative. In the arc require less separation and larger ones an increased separation. At this stage the arc is quiet, with good pure carbons very steady, and the potential difference remains at about 45 volts, if, of course, the carbon is properly fed to make up for combustion. The perfect arc is really a beautiful phenomenon. While the positive carbon still loses by volatilsation from its tip or crater and by combustion from its sides, the negative gains no deposit, but wastes at a less rate than the other, and by combustion only. The carbon vapour carried

off from the positive is consumed by the oxygen of

the hot vapour stream of flame takes the part of
the bath, and probably acts by molecular inter-
changes of carbon atoms in molecules of carbon to
cause the transfer which occurs, just as in the
plating bath the molecules of the plating compound
are polarised and allow atomic interchange, which
results in conveyance of metal through the bath.

THE DOW STEAM TURBINE MOTOR.

Fmost interesting exhibits at the recent National

ROM a technical point of view, one of the

Electrical-Light Convention in Providence was the

The motor case has two partitions, which, with the two covers, divide the interior into three parallel chambers. Stationary guide-plates, analogous to those of the water turbine, are arranged upon the outwardly presented face of each partition in six series concentric with the shaft, and the several series are separated from each other by annular spaces. Two steel wheels are mounted upon a sleeve whose bore has two opposite grooves to receive at a sliding fit two corresponding features upon the driving-shaft. The hubs of the wheels project inward into the central chamber through hubs. Upon the inward face of each steam wheel holes in the partitions which are larger than the are series of buckets concentric with the shaft and Thus the faces of the moving buckets seat upon the

projecting into the annular series of guide-plates.

the air before it can deposit on the negative. Hence, the outer zone of flame, which can easily be distinguished from the central zone or arc flux proper, is probably a zone of combustion similar to that existing in ordinary flames. The removal of carbon by evaporation from the positive end gives rise to the crater or cup which is so prominent a feature of carbon arcs produced by continuous currents. The size or area of the crater is a rough measure of current strength, but varies with different qualities of carbon. With very long arcs the crater or hollowed end disappears and the ends become rounded. A well-formed crater with the arc or flame confined thereto means usually a steady light, since the chief source of light in an electric arc is from the positive crater, which shines like a diminutive sun and represents the hottest part of the arc. The vapour light proper or flame light is comparatively very feeble, and of a purple quality in air. Hence, the arc light is as truly an incandescent source of light as is the incandescent carbon filament, with the difference that to run the latter at the temperature of vaporisation of boiling-point of carbon, so to speak, means instant destruction, while by the necessities of the case the light obtained from the arc is chiefly that emitted from a surface of carbon at its temperature of boiling, or, more correctly, of sublimation at atmospheric pressure. This temperature is exceedingly high, and accounts for the well-known superior economy in light proHuction of the arc over all other kinds of lighting. The temperature of the positive carbon crater is so high that the carbon exists there in a soft or plastic ondition capable of receiving an impression like utty. I have proved this with very large arcs of 50 to 200 ampères by suddenly forcing the carbons ogether when the current had been cut off, and display of the new and remarkable steam turbine bottom of the annular spaces of the partitions, and nding that they would fit each other perfectly, the manufactured by the Hotchkiss Ordnance Company the faces of the stationary guide-plates seat upon egative impressing its form on the positive crater. under the Dow patents. The following description the bottom of the annular spaces of the steam As an interesting fact in this connection I may of the machine and its operation, furnished by the wheels. tate that I have been able to bend carbon sticks inventor himself, will be of interest to our readers: Fin. to in. in diameter by passing current-In external appearance the service motor is a rough them of sufficient amount to almost aporise the sticks and cause them to emit an tensity of light approaching that of the arc. These facts would point to the possible fusion of

LAYOUT OF VENTS:

VENTS IN ONE STA AND ONE REV DISC TO BE RIGHT HAND.
VENTS
LEFT

FIG. 2.

In the central chamber, midway between the partitions, is a disc mounted upon the sleeve; and short cylinder 9in. in diameter by 5in. long, having on each side of disc, distant from it 015in., is the bulging covers, in whose hubs the driving-shaft is inner face of the partition, or rather, the inner face journalled. The steam-pipe enters at one side of of an annular face-plate, whose hub screws into its the case, and the exhaust-pipe leads out beneath. I partition. The disc part of each face-plate stands

clear from its partition, and is perforated by three concentric rows of holes, and the inner face of each face-plate is channeled in concentric circles between the holes and cross-channelled by radial grooves, starting near the periphery of the face-plate, and running between the perforations.

SCIENTIFIC SOCIETIES.

Steam from the boiler enters the central chamber, passes through the disc-like ports or spaces between the central disc and the face-plate on each side of it, as well as through the perforations in the faceplates, flows along the channels in the face plates Mr. Knobel read a paper by A. A. Rambaut on to the annular space surrounding the wheel hubs," The Determination of Double-Star Orbits from then right and left toward each wheel, then ex- Spectroscopic Observations of the Velocity in the pands radially outward through the zigzag of Line of Sight." The general conclusion arrived at alternate guide-plates and buckets, until finally it was that, in order to determine the ellipticity and exhausts from the circumference of the steam position of the orbit, the separation of the lines seen wheels into the outer chambers, the exhaust pipe as double in the spectrum should be measured not and the atmosphere. only when the separation is a maximum, but at other times at equal intervals of time before and after greatest separation.

The least disturbance of the steam wheels in the direction of their axis partly closes one of the steam ports, and at the same time opens wider the other port, thus reversing the disturbance, and forcing the wheels back to their normal position. But, He has succeeded in observing the close companion and the scale are seen on the plate. The scale since the feathered driving-shaft slides freely through the sleeve, any external push endways of the shaft does not disturb the wheels, and in the service motor the shaft is slipped out of clutch at full speed of the motor. In practice only 1ogin. end play is allowed to the wheels, and the automatic

balance is so accurate that the wheels do not wear

against their seats, so that months of use have

brought no increase of end play.

Burnham on
Mr. Knobel then read a paper by Mr. S. W.
"The Companions of Aldebaran."
during its periastron passage with the great Lick
refractor, and in measuring its distance and position
angle. He estimates that when closest to its
primary it was at a distance of only 0-13". The
paper was accompanied by a diagram representing
the earlier observations of position angle and dist-
ance, which indicated satisfactorily an elliptic orbit.
The President said: It is a great triumph of
observation that so satisfactory an orbit should be
deducible of a star whose greatest distance from
its primary does not amount to half a second, and
it speaks strongly in favour of the definition of the
great Lick telescope, as well as of Mr. Burnham's
assiduity, that the observations of such small
quantities should fall so well together. A few years
ago it would not have been thought possible.

we begin to think of it, and that is, in order to get the position of the centre of the plate accurately, we must allow for the projection of the sphere on the ROYAL ASTRONOMICAL SOCIETY. tangent plane on the plate taking the co-ordinates HE March meeting was held on the 13th inst., angular co-ordinates in the tangent plane, but we of the guiding stars. We are dealing with rectTGeneral Tennant, President, in the chair. A and declination. The Thomas R. Clapham, of Austwick Hall, near Settle, next is the scale of lines which is to be printed on Yorkshire, and Arthur Kennedy, of 1, Clement's the plate. Two very fine scales on glass have been Inn, W.C., were elected Fellows. received from Prof. Vogel, and one has been mounted. This work has proceeded rather slowly, because we have had to arrange these various thingsstep by step. This scale consists of a number of lines ruled on the glass plate at right angles at a distance of 5 millimètres, cutting through a silver film, and then the photographic plate is put next to the silver ruled plate and placed in front of the object-glass of the photographic telescope, and, by means of an incandescent electric lamp, the scale is printed on the photographic plate. It is not developed then, but is preserved in a dark box, and afterwards exposed, and, on being developed, both the stars plate, and also determining any distortion of the serves for giving reference lines for stars on the film. We found with this that very beautiful impressions are obtained, and there is no doubt the method is perfectly successful, and I think our best thanks are due to Prof. Vogel for having worked out this valuable adjunct to the photographing of the heavens. One point discussed has been the determination of the errors of the scale, because we do not like to assume it had been ruled perfectly: these have been determined so far that we know that the errors are very small; that is, the spaces between the different lines are sensibly equal, within quantities which approach the limit of errors of observation, and that the equality obtains throughout the whole length of the lines-that is, they are parallel curves There is another interesting point, and that is the course of the work in relation especially to the weather. The weather this year has not been st all favourable. We have been very much hampa by cloudy weather and the severe winter, February, although we had many fine nights, re was a good deal of fog, so that I hope we have not had a fair sample of the work which will be done. From Feb. 9 to March 12 there were 29 nights' ontinuous watch, 15 of these were clear, three we partially cloudy, and 11 were available in s degree for photography, though several of the were more or less foggy. On these nights 21 plates were exposed for star trails or regular photographs representing an exposure of 12h. 49m. Better results will be obtained as the work becomes more familiar. It is important to bear in mind the difficulties there are in carrying out this work because I think some gentlemen who have looked at it from a theoretical point of view have suggested going beyond the 14 mag., and giving an increased exposure, which would add very materially to the difficulty of getting through the work. One of the resolutions of the committes was that each observatory was to select the bat

In actual operation the performance of the motor is almost startling. It was shown under steam at the works of the Hotchkiss Ordnance Company, both in place on the frame of the Howell torpedo and set up for experimental purposes connected to the torpedo flywheel. The Howell torpedo, that has been adapted for use in the United States Navy, as is known to most of our readers, derives its motive power from the stored-up energy of a heavy flywheel that is driven up to an enormous velocity" Variations of Latitude deduced from Observabefore the torpedo is fired. The flywheel of the service torpedo weighs about 1351b., and the energy stored is said to be equivalent to about 18H.P. One of the standard motors coupled to such a flywheel, and running under 701b. of steam, brought the wheel up to its full speed of 10,000 revolutions per minute in the brief space of two minutes and forty-eight seconds.

Twenty-five horse-power is, as has been mentioned, claimed for this motor at 1001b. steam pressure; but it is only fair to say that it has never been given an exact test, owing to the enormous difficulty of dynamometer work at the extreme speed developed. The steam consumption claimed is 45lb. per horse-power per hour. As this is presumably based on the 25H.P. estimate, it will be raised or lowered as exact tests show more clearly the real capacity of the machine. The feature of the motor to which it owes its mechanical success is unquestionably the arrangement of admission ports, by which steam cushions are formed to obviate end plates and keep the moving parts always clear of the stationary parts. This enables the clearance space to be reduced to a very small amount, and hence obviates the great waste of steam by leakage, that has proved so formidable a foe to previous steam turbines. Just how well the steam is utilised in the multiple expansions it undergoes it is impossible to say without exact tests. The operation of the motor under its full speed is remarkably smooth and quiet.

Fig. 1 shows a section of a standard motor as arranged for driving the torpedo fly-wheel. The course of the steam is from the boiler to the annular space in the centre of the motor, then laterally through the ports mentioned in the inventor's description through the narrow cushion spaces, and then, passing on either side to the inner ring of the turbine, it expands through the central chambers and then passes into the exhaust.

Fig. 2 shows in diagram the arrangement of the standard motor with the lay-out of the vents in the several rings. The steam is actually expanded down so that in the exhaust it shows less than 1lb. by the steam-gauge.

A paper by Prof. Bakhuyzen was read on tions of Polaris made at Greenwich 1851-1889."

Mr. Turner said: The question has recently been raised in Germany as to whether there is a real change in latitude of places on the earth's surface with a yearly period of about a year, or whether the observations which appear to indicate such a change may be reconciled by assuming that there is only a periodic change in the refraction of the earth's atmosphere. It has been suggested that all question as to a change of refraction might be eliminated by observing stars to the North-that is, below the Pole-as well as on the meridian to the South. There are some who claim that when refraction is so eliminated there still remains evidence of a change of latitude. Prof. Bakhuyzen bas in this paper been discussing the Greenwich observations which have been made on one side of the Pole only. In Berlin they had found that the annual change seemed to be greater in 1879, 1884, and again in 1889, and Prof. Bakhuyzen seems to think that the Greenwich observations-though not made in a way in which the variations of refraction can be eliminated-indicate that in 1879, 1884, and 1889 were epochs of greater disturbance.

The Astronomer Royal was called upon by the president to give an account of the preparations being made at Greenwich for the photographic survey of the heavens. He said: I thought it might be interesting to the Fellows to hear, as we are now at Greenwich beginning operations for the astro-photographic chart, what the state of our preparations are, and how far we have got, because it is a question in which one must proceed tentatively, and there is a great deal to be worked out. With Mr. Turner's assistance, this paper has been drawn up on the subject, and has been divided into different heads. The first important matter was to make a catalogue of guiding-stars, by means of which the telescope might be fixed with the centre of the plate in a definite position, so that we should have the centres of each plate in the selected position on the heavens, and be able to form a map. That is a matter which is not so simple as it appears at first. Prof. Bakhuyzen went into the question, One of the steam turbines is now in use in the and from his trials on a particular zone he came to United States Torpedo Station at Newport, the conclusion that he might proceed so far as 22 operating at the full speed of nearly 10,000 revolu- minutes from the centre, and be able always to get tions per minute a dynamo originally intended for a sufficiently bright star within that distance; but use with the Parsons steam turbine. The appear- we found there would be a great advantage in ance of the larger sizes of this machine will be extending the distance from the centre to 30 awaited with great interest, for a successful minutes. In the Greenwich 30in. equatorial there is rotary engine has advantages that need no a 10in. guiding telescope, and it is proposed to take, comment. Even if its efficiency should prove where possible, a star not fainter than 9th mag. for considerably less than what is expected, the setting purposes; but in some cases it is necessary to cheapness and compactness of the machine will go down to 9. In the paper which has been drawn go far to outweigh such a disadvantage. It is up a number of guiding stars are given of different hardly to be expected that the steam can be ex- mags., according as you take 22' radius or 30 panded as advantageously in such an apparatus as radius from the centre; and if we take 22' in this in the ordinary steam cylinder, particularly as it is zone with which we are concerned, there will be 90 necessary to wire-draw it slightly in passing through stars of 9 mag. of Arglander's catalogue, which each of the consecutive sets of vents in order to give really means anything down to 10th mag, while the emergent jet velocity enough to compensate for there are only 28 stars of the 9th mag. within 30 the greater tangential velocity at the next ensuing radius, so there is an obvious advantage in extendring. As it stands, however, it is a most remarking the distance from the centre. That is one able machine, and its progress should be followed important point. There is another point that has with the closest attention.-Electrical World (N.Y.) to be borne in mind, and which is obvious as soon as

plates that could be obtained. No decision was
come to as to what maker the plates were to be
obtained of, and accordingly at Greenwich the
following plates have been tried-several Wratte
and Wainright, the Seed Company, and we are
now using the Star plates. Our thanks are due to
the various makers for the trouble they have tak
in cutting the plates to the proper size. The sele
tion of the best plates for the work has been a
matter of difficulty; but a slight preference f
for the Star plates. Then there is another question
with respect to the time of exposure required to get
the different magnitudes of stars. The resolation
of the committee was to obtain the exposure which
would give stars of the 11th mag. Plates have bee
exposed in the region assigned to Greenwich, which
has a fixed zenith distance, first with an exposure of
30m., and 6m., and 1m. respectively. Mr. Turner
has examined the northern half of these plates and
measured the diameters of the stars, and he finds the
stars in Argelander were shown with 1m. exposure
except one. The plate gave all the stars down to
what Argelander calls 94 mag., which is practically
10th mag. Mr. Turner arrives at a conclusion
which may be of some interest. Fellows may be
aware that there has been a question as to whether
the diameter of a star disc varies as the square
root of the time of exposure, or as
root; and from an examination of these plates Mr.
Turner finds that, comparing 30m. and 6m. exposure
the diameter varies between the cube root and the
4th root. The value of 33 was adopted in the
formula, and from that what may be called the
constant of the plate is determined, and thence s
deduced a time of exposure which would be
required to give the photographer certain diameters
of certain mags. of stars. Taking the smallest
diameter of the disc as 2, 12m. would be required
to give stars of the 14th mag. 8 of a minuts
for stars of the 11th mag., and 7 second
for stars of the
9th mag. It must be
understood that these results are quite pre-
liminary: but they represent a fairly average night,
and they give us some information. The following

the cube

Mr. Mayall said that since the last meeting he had received another notification from the authorities of the Antwerp Microscopical Exhibition giving further details than those which he was able to communicate at the last meeting of the Society. From this it appeared that the Exhibition was to be open during August and September next, and the proposed mode of classification was given. The general arrangement was into ten classes, of which Class I. Class II. would comprise every kind of illuminating was devoted to microscopes and current research; apparatus; Class III., apparatus for photomicrography; Class IV., goniometers, adapters, and spectroscopes; Class V., measuring apparatus; appliances; Class VIII., microscopic preparations; Class VI., microtomes; Class VII., dissecting Class IX., bacteriology: Class X., works on the microscope. It would be seen from this that the

exhibition was intended to be pretty exhaustive, and if in each class there was only a moderate representation, the whole would be likely to form a very interesting collection.

Prof. Bell said they had also received from the General Secretary of the International Congress on Hygiene, to be held in London in August next, an Society at the meetings, and thinking it very deinvitation to appoint delegates to represent the sirable that they should be so represented, the Dallinger to undertake the duty. This congress, Council had requested the President and Dr. he might mention, was the 7th of a series which had been held in all the great countries of Europe except

Great Britain, and it was expected that the forth

coming gathering would be one of the most important yet held.

The President announced that arrangements had

been made to hold an exhibition meeting and conversazione of the Fellows of the Society on the evening of Thursday, April 30th.

QUEKETT MICROSCOPICAL CLUB. Tmeeting of this club was triday HE two hundred and ninety-first ordinary March 20th, at 20, Hanover-square, W., Dr. W. H. Dallinger, F.R.S., president, in the chair. The minutes of the preceding meeting was read and confirmed. Five new members were elected by ballot, and ten proposals for membership were read, and suspended until the next meeting. The additions to the library since the last meeting were

announced.

Mr. Karop gave a short description of the method of making etched glass discs for use in drawing objects under the microscope. By the use of this simple and well-known contrivance, and so-called sectional paper, almost anyone could make respectable and truthful representations of microcopic specimens.

Mr. Nelson exhibited a new student's microscope with adjusting sub-stage made by Mr. Baker, of Holborn. He claimed to have been the first to advocate the application of a rack-focussing adjust ment to the English Hartnack model student's instrument, which addition, however, at the time, just about doubled the cost. The present instrument, although possessing no new features, was a successful endeavour to provide one capable of very highclass work at a reasonable price, and the thanks of those requiring such an instrument were due in the present instance to Mr. C. Lees Curties, who, he believed, was mainly responsible for it. Mr. Nelson exhibited and described a number of very beautiful photos of diatom structure, shown on the screen by the gas lantern. Amongst them was a process of an Auliscus which he had long endeavoured to resolve into secondary structure without result. He had at last succeeded, and it exhibited the usual perforations. Another was P. angulatum mounted in piperin, a medium of high refractive index. This possessed the singular property of greatly interfering with the colour correction of homogeneous immersion lenses, and he at first thought some accident must have happened to a fine apochromatic he was using, which, on this

piperin-mounted specimen was not even achromatic, so great was the disturbance. It did not seem to interfere with the colour correction of dry objectives, or to a much less extent, while detail was brought out to a marvellous degree by this mountant, making dry lenses almost equal to immersions when used on balsam or styrax mounts. A vote of thanks was passed to Mr. Nelson for

his exhibit. Announcement of the fixtures for the

ensuing month was then made, and the proceedings

terminated.

AN ink which, according to the Effective Advertiser, seems to be identical with the disappearing ink of about twenty years ago, has recently been placed upon the European market, and is a watery solution of iodide and amylum (sic). It produces beautiful blue-black writing, which begins to fade after a few days, and disappears entirely after the lapse of a week.

About Circular Saws.-Every sawmill man knows that one of the most difficult and trying operations to which circular saws are put is that of log cutting, working up the rough timber into lumber. But not all sawyers are as familiar with the conditions which govern the operation of the circular saw as they should be. These are the only tools used in cutting and dressing lumber that within themselves have certain inherent conditions to govern their speed, and a knowledge of this is an important part of a sawyer's ability and education. A great deal, of course, depends upon the material and manner in which the saw is made,

SCIENTIFIC NEWS.

gardens there during 1890. There are now 1,342 species, besides plants not yet determined. The second International Ornithological ConTHE HE completion of the London-Paris tele- gress is to be held at Budapest from May 17 to phone is an achievement that deserves 20. The headquarters are at the National ported to be clear and distinct, although the especial notice, because the "speaking" is re- Museum. instruments best suited for the work have not yet been selected. On the French land line, D'Arsonval's apparatus has given good results, as the Gower-Bell has on this side. The cable contains four separate conductors, each containing seven wires of as pure copper as could be obtained, and, with the covering, weighs for each core 460lb. to the nautical mile. The resistance is about 7.5 per knot, while the insulating resistance from wire to water is about 500 megohms per knot, both at a temperature of 75° Fahr. So far the experiment is a decided success, and it is probable that other cables will be laid and arrangements be made for effecting telephonic communication with Berlin and Vienna. Whether the existing line will be commercially successful remains to be seen, for certainly ten francs is a high price for three minutes' use of the line.

The Council of the Society of Arts will award the Albert medal early in May, and they invite members to forward to the secretary, by April 18, the names of those they think worthy of the dis

tinction.

The Geologists' Association have made arrangements for an excursion to the Isle of Wight at Easter, and other excursions, which will afford much pleasure to those who can spare the time, are being arranged for the summer months.

The death is announced of Capt. Daniel Pender, F.R.G.S., the assistant hydrographer to the Admiralty. The deceased, who was only 58 years of age, had an unrivalled knowledge of the Pacific Ocean, on which "station" he passed many years of active service.

Klein on

A course of four lectures on "The Dynamo'
will be given by Prof. S. P. Thompson, at the
Royal Institution, on Saturdays, at 3 p.m., from
April 11 to May 2. The Tyndall lectures
will be delivered by Dr. E.
Tuesdays, April 28, May 5 and 12, the subject
being the popular one of Bacteria: their Nature
and Functions." Prof. Dewar is to deliver six
"Recent Spectroscopic Investiga.
tions" on Thursdays, from April 9 to May 14,
and Mr. H. Graham Harris, M. Inst. C.E., will

lectures on

66

66

66
notice
we

deliver three lectures on the "Artificial Produc-
tion of Cold" on Saturdays, May 9, 16, 23. The
Friday evening meetings, to which only mem-
bers and their friends are admitted, will
recommence on April 10, when Sir W. Thomson
will discourse on "Electric and Magnetic
Screening." Amongst the other "discourses"
already announced,
Magnetic
Rocks," by Prof. A. W. Rücker, F.R.S.; on
April 17, Liquids and Gases," by Prof. W.
Ramsay, F.R.S.; on May 8, "Crystallisation,"
by Prof. G. D. Liveing; on May 15, "The
Molecular Process in Magnetic Induction," by
Prof. J. A. Ewing, F.R.S.; on May 22,"An
Astronomer's Work in a Modern Observatory,"
by Mr. D. Gill, F.R.S.; and the "Rate of Ex-
plosion in Gases," by Prof. Harold Dixon,
F.R.S., on June 12. On June 5, Prof. St.
George Mivart, F.R.S., will deliver the dis-
course, but the subject is not yet announced.
Altogether, what may be termed purely scientific
subjects are well represented in the lists for the
Admission to the four
lectures by Prof. S. P. Thompson on the dynamo
can be obtained for half a guinea.

"after-Easter" season.

other day, Miss Gosset read a paper on
At a meeting of the Huguenot Society the
Family of Modellers in Wax," in which she
"A
gave an account of the introduction of wax-
modelling into England by the Huguenots, and
the successful practice of the art by several
members of the Gosset family. The art has now
fallen into decay; but the specimens exhibited
may help to revive a taste for it.

whether it has been hammered "tight" or "slack"
on the periphery. Assuming that on account of
the centrifugal force the steel is stretched from the
eye of the saw towards its periphery, a great deal
would depend upon the condition of the saw at the
beginning. A saw that is hammered loose at its
periphery can be operated at a much higher speed
than one that is tight or stretched. In explaining
this, let us suppose that a saw is started up and
gradually increased in speed. For a time, and up
to a certain limit, according to the above con-
ditions, the stiffness of rigidity of the blade will be
increased. Above this limit it begins to diminish,
and at a very high velocity the plate becomes limber
and pliant as a piece of paper, and if the speed is
kept up, the periphery of the saw will assume an The Mechanical Workshops Syndicate of Cam-
undulatory or wavy motion. When in this condi-bridge University have issued a scheme of
tion it is as sensitive to pressure on its side as if it practical and theoretical instruction in engineer-
were made of a sheet of paper. This, while it may ing; but as a sum of £20,000 will be needed for
form an interesting experiment, is also valuable in the establishment and equipment of the neces-
consideration of the subject of speed for such sary laboratories, the bulk of the funds will have
ls. It shows beyond a doubt that there is a to be provided outside the University.
c speed at which saws should be run to do
to the best advantage and within the limits
ety and economy.-Manufacturers' Gazette.

The Kew Bulletin for March contains a list of the orchids that flowered in the houses and

A new method of extracting aluminium is announced, the discovery of Mr. H. Greenway, of Joplin, Missouri. The new process is described as being carried on by contact with the air in contains a retort in which the clay is distilled, two furnaces, separately heated, one of which and the other a peculiarly constructed and arranged reduction chamber composed of rethe shell or chamber is a long rectangular prism, fractory fireclay lined with magnesia. In shape the rectangular planes of which approach very nearly to each other, thereby permitting the charge (carbon) to be quickly and highly heated. The distilling-retort is charged with a mixture of bituminous coal and ordinary clay previously dried. The furnace is then heated to a degree The reducing-chamber is charged with a suitable sufficient to generate gas without fusing the clay. form of carbon. Heat is then generated from coke in the furnaces, and by the assistance of a blast is raised to a temperature of over 2,000° Fahr. After the watery vapour has passed away, the "alumina vapour," together with the coal-gas, is decomposed, and in passing through the heated chamber is reduced to the metallic state."

According to the inventor, alumina, as it exists in clay, is found in a high state of sublimation, and here lies, the inventor says, the key of the whole mystery which has baffled all attempts at direct reduction analogous to most metallurgical operations.

An exhibition will be opened at Launceston, Tasmania, on Oct. 14, under the patronage of the Governor. The executive committee, composed of many of the leading men in Tasmania, and a London committee, presided over by Sir Edward Braddon, K.C.M.G., the Agent-General for the colony, are actively at work. The scope of the facture; but especial attention will be given to exhibition embraces every branch of manuall classes of mining plant. hibits at reduced rates. Medals and certificates ments have been made for the carriage of exwill be awarded. Applications for space should be made at the earliest possible date to the hon. secretary of the Tasmanian Exhibition, 5, Victoria-street, S. W., from whom all information can be obtained.

Special arrange

The Council of the Animals' Institute have decided to hold exhibitions of appliances used in the working of horses with the object of lessening suffering amongst animals employed in traffic. Prizes will be given for the best collection of bits and of horseshoes, and inventions coming under the head of harness. The "best" in these

competitions will be the most humane and practical. The first exhibition will open on April 6.

Union Elevated Railroad Company lately ran American papers state that the Brooklyn their compound engine for ten days against a lot of the best simple locomotives on the road. The coal used was all weighed. At the finish of the test the compound was found to have effected a saving of 23 per cent. compared with the average coal consumed by the other engines.

The superintendent of motive power on the Pennsylvania Railroad is credited with the opinion that with a perfect roadway American locomotives would do 80 miles or more an hour

with fair-sized trains. As he has heard that 90 miles an hour is "common" in England, and appears to believe the statement, the opinion is possibly not worth much.

At a recent meeting of the American Institute of Electrical Engineers, Mr. O. T. Crosby read a paper on high-speed electrical railways, in which he gave an account of experiments made on a circular track laid at Laurel, Maryland, the gauge being 28in. A speed of 120 miles was obtained, and Mr. Crosby has little doubt that with a firmer roadbed 150 miles an hour is quite within the powers of a well-designed electrical railway. The experimental car seems to have been "derailed" rather often; but that is a defect due to the road rather than to the high speed of the car.

An exhibition which may have important results is that to be held at Palermo from Nov. 1 next, until May 31, 1892, as a special feature