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from subjecting its phenomena to the sume method oí investigation as other natural phenomena; its disorders were thought to be an incomprehensible affliction, dne to the presence of an evil spirit in the snfferer, or to the enslavement of the soul by sin, or to anything bat their true cause—bodily disease. Consequently, the treatmont of the insane was not in the hands of intelligent physicians, but was given np to coarse and ignorant gaolers, whose savage cruelties will for all time to come be a great and ugly blot upon the enlightenment of the age which tolerated them.

Matters are happily changed now. On all hands it is admitted that the manifestations of mind take place through the nervous system; and that its derangements are the result of nervous diseaso, amenable to the same method •if investigation as other nervous diseases. Insanity has accordingly become a strictly medical study, and its treatment a branch of medical practice. Still it is all too true that, notwithstanding we know much, and are day by day learning more, of the physiology of the nervous system, we aro only on the threshold of the study of it as an instrument subserving mental function. We know little more positively than that it, has snch function; we know nothing whatever of the physics and of tho chemistry of thought. The conception of mind аз a mysterious entity, different essentially from, and vastly superior to, the body which it inhabits and uses as its earthly tenement, but from which its noblest aspirations are to get free, still works openly or in a latent way to obstruct tho study of its functions by the methods of physical research. Without speculiting at a'\ concerning the nature of mind— which, let me distinctly declare at the outset, is a question which science cannot touch, nnd I do not dream of attempting to touch,—I do not shrink from saying that we shall make no progress towards a mental science if we begin by depreciating the body, not by disdaining it, as metaphysicians, religious ascetics, and maniacs have done, bnt by labouring in an earnest and inquiring spirit to understand it. shall we make ацу step forward; and when wc havo fully comprehended its functions, when we know how to estimate fitly this highest, most complex, and wonderful achievement of organised skill, it will bo quite time, if there be then any inclination to look down upou it with contempt.

The truth is that in inquiries concerning mind, as was once the case in speculations concerning othor natural phenemena or forces, it has been the practice, to begin where the inquiry should have ended. Just us the laws of physical actions were evoked out of tho depths of human consciousness, and the relations of bodies to one another attributed to sympathies and antipathies, attractions and abhorrence«, iustoad of being acquired by patient observation aud careful generalisation, so lins a fabric of mental philosophy been reared in the doubtful revelations of selfconsciousness, in entire disregard of the more tedious und less attractive duty of observation of facts, and induction from them. Surely it is time we put seriously to ourselves the question whether the inductivo method, which has proved its worth by its abundant fruitfulness wherever it has been faithfully applied, should not be as rigidly used in the investigation of mind as in the investigation of other natural phenomena. If so, we ought certainly to begin our inquiry with the observation of the simplest instances—with its physiological manifestations in animals, in children, in idiots, in savages, mounting by ■logrees to tho highest and most recondite facts of consciousness, the interpretation or the misinterpretation of which constitutes what has hitherto claimed to be mental philosophy. The inductions which wo get by observing the simple may be used with success to disentangle the pheliDmonaof the complex; but the endeavour to apply tho complex aud obscure to the interpretation of the simple is sure to end in confusión and error. The higher mental faculties are formed by evolution from the more simple and elementary, just as the more special and complex structure proceeds from the more simple and general; and in the one case as in the other we must, if via would truly learu, follow the order of development Not that it is within my present purpose to trace the plan of development of our mental faculties, but the facts and arguments which I shall bring forward will prove how vain and futile it is to strive to rear a sound fabric of mental science on any other foundation.

To begin the study of mind, then, with the

observation of its humblest bodily manifestations, is a strictly scientific method. When we come to inquire what these nre, it is far from easy to fix the point at which mental funct'ons begin. Without doubt, most of the actions of man, and many of those of the higher animals, do evince the operation of mind, but whereabouts in the animal kingdom it first appears, and what part it has in the lower nervo functions of man, are questions not easily answered. The more closely the matter is looked into, the more clearly it appears that we habitually embrace in our conception of mind different nervous function?, some of which proceed from different nerve-centres, and the more necoesary it becomes to analyse these functions, to separate the more simple and elementary, and to discover in the concrete as much as possible of the meaning of the abstraction. Is the brain the exclusive or^an of mind? If it be so, to what category of functions shall we refer the reilex acts of the spinal cord, which take place independently of the brain, and which often achieve as definite an end, and seem to display as intelligent an aim, as any conscious act of volition? It needs not to illustrate in detail tho nature and oxtent of reflex action, which is familiar enough, bnt I may select a striuing example in order to serve as a text for the reflections which I wish to bring forward. One simple fact, rightly understood and truly interpreted, will teach as much as a thousand facts of the same kind, but thü thousand must have been previously obsarvod in order to understand truly the one; for it is certainly true that to apprehend the full meaning of common things, it is necessity to study a great many uncommon things. This, however, has been done in this instance!))* the distinguished physiologists whose labours have fixed on a tolerably firm basis the doctrine of reflex action ; we may, therefore, take as our starting point the accepted results of their labours.

It is well known that if the hind foot of a frog that has had its head cut off be pinched, it is withdrawn from the irritation. Tho stimulus to the afferent nerve reaches the grey matter of the spinal cord, nnd sets freo a force which excites to action the corresponding motor nerves of the same side. When the foot is pinched more strongly, the force liberated by tho stimulus passos across the cor« to the motor nerves of the opposite si'le, and there is a simultaneous withdrawal of both limbs; and if the excitation be stronger still, there is a wider irradiation of the effects of the stimulus in the grey matter, and a movement of all four limbs following, the frog jumping away. Theso movements of the decapitated frog, which it is plain effect the definite purpose of gotting it out of the way of harm, we believe to bo analogous to the violent coughing by which food that has gone the wrong way is expelled from the human larynx, or to the vomiting by which offending matter is ejected from the stomach. Independently of consciousness and of will, an organism plainly has the powor—call it intelligence or call it what we will —of feeling and eschewing what is hurtful to it, as well as of feeling and choosing what is beneficial to it.

But the experiment on the frog may be made more striking and instructive. Tnuoh with acetic acid the thigh of n decapitated frog ovor the internal condyle, and the animal rubs it off with the dorsal surface of the foot of the same side ; cut off the foot and apply the acid to the same spot, and tho animal tries to get at it again with ita foot, but of courso, having lost it, cannot. After some fruitless efforts, therefore, it give» up trying in that way, seems restless, as though, says Pflüger, it was seeking seme other way; and at last it makes use of the foot of the other leg, and succeods in rubbing off the acid. Notably we have here not merely contractions of muscles, but combined and harmonised contractions in due sequence for a special purpose. Thoie are actions that have all the appearance of being guided by intelligence nnd instigated bv will in an animal the recognised organ of whose intelligence and will has been removed.

(To be continued.J

VANADIUM.

PROFESSOR ROSCOE, F.R.S., delivered on the 21st of April last a lecture on Vanadium, lu fore the Chemical Society. This metal, he sa<l, was discovered in 183Ö. by Sefström, in the celebrated Swedish bar-iron made

from the Tabcrg ore. Sefström ascertained some t of the mo-t peculiar characters of this substance, proved it to be a new element, and prepared some of its compounds in the pure state. The reactions by which vanadium can be separated and distinguished from ail the othor elements are:— 1st. The formation of a soluble sodium vanadate» when tho vanadium compounds are fused wit К sodium carbonate. 2nd. The formation of an' soluble ammonium vanadate when sal ammonj is added to the solution of a soluble vani 3rd. The prodaotion of a splendid blue ^H 1 when this anuawium salt, dissolved U%ylie> chloric acid, is warmed with reduebjg Rgents, such as oxalic acid.

Sefström, not hiving leisure to prosecute the full examination of the properties of the new metal, handed over his prerwratioae to Berzelius; and it is to the investigations of the great Swede that we owe almost all our acquaintance witb the chemistry of vanadium.

Since Bcnselius"s time, vanadium has been discovered in many minerals, of which a lead ore containing lead vanadate, and called by the mineralogists, vanadinite, is the most important.

In lsfio Professor Roscoe came into possession of a plentiful source of vanadium, in a by-product obtained in the preparation of cobait from the copper-bearing beds of the lower Keupex Sandstone of the Trias, at Alderley Edgo, in Cheshire. Following, in the main, "the ргосая of preparation adopted by Sefström, Professor Roscoe obtained, from the above-mentioned source, several pounds of pure ammonium vanadate, from which all the other compounds of vanadium can be prepared.

What, now, were the conclusions to which Berzelius arrived, from his experiments concerning the constitution of the vanadium compounds? He assigned to its three oxides the formube VO, VOj, and VOj, whilst the chloride was represented by VCI'. The atomic weight of the metal he found to be V = C^'Â

Some years afterwards. Rammeleberg' observed that vanadinite, a double salt of lead-vanad.ate and lead chloride, is isomorphous with apatite and with mimitcsite, the former containing phospkoric, the latter arsenic acid. ТЬЛз cristallographie analogy would load us to conclude that tho oxide of vanadium in the vanadinite has the formula V,Os, agreeing with the corresponding oxides of phosphoros and arsenic, P.O» and AsiO5; but the unyielding chemical fact of Berzelius compel us to view the oxide in question as VO'. It was, then, evident that here was either an exception to the law of isomorphism, or else Berzelius's views were erroneous.

Professor Roscoe, in order to endeavour to clear up this question, had carefully repeated Berzelius's experiments, and he found them confirmed in every particular; but, having pursued tho subject further than Berzelius, he hod succeeded in obtaining the key to the enigma presented by the above anomalous crystallographic relations.

The lecturer has proved that the substance supposed by Berzelius to be vanadium is not the metal, but an oxide, and that the tme atomic weight of the metal is 51-3. The vanadic acid, VO1, of Berzelius, hence, becomes VjO5, corresponding to PsO5, and As»05; and the abovementioned isomorphism is fully explained. The sub-oxide of Berzelius is atri-oxide, V.Oj; whilst tho terehloride (VCI3) of Berzolius is an oxychloride, VOCl.t, corresponding to oxychloride of phosphorus, POClj.

Professor Roscoe has succeeded in obtaining bromine and iodine compounds of vanadium, and also various metallic vanadates. He went on with his lecture by pointing out that the chiracters of tho vanadates bear out the analogy of the vanadic acid with the highest oxides of phosphorus nnd arsenic; and stated, in conclusion, that vanadium, hitherto standing iu no definite relation to other elements, must now be regarded as a member of the well-known triad class oi elementary substances, comprising nitrogen, phosphorus, boron, arsenic, antimony, and bismuth.

DRESSING MILLSTONES WITH THF. DIAMOND OR "BORT."

( Continued from jiagc 153.)

GOLAY'S machine was generally admitted to be a great advance on anything previously proposed, and many millers adopted it under thi» impression that nothing better could be obtained; others, however, waited, seeing that there still retftects connectai with the dressing operar that imtchinc did not remove, and also of other plans that very soon made their i им the commercial success of Golay's ; generally known. f's machine supplied one desideratum, in f a dress superior to what could be obtained , in puttiug in the dress or cracking on stone in clean, straight, unbroken, uniform and in less time than by hand, and it great advantage of making the mill ers less dependent on the individual skill of "НЬ шяп. Notwithstanding these great advances. however, many millers consider that the ■ is defective in many of its details, more specially in not tending to keep 'he millstones in better track or level than formerly. The machine rests on three small feet, and is, consequently, dependent for its level on the small local spots whereon those feet happen to be placed, and can in no way check or correct the inequalities which escape the proving staff. As the machine is worked by power it is impossible to use it while the mill is standing, that is at the very time when a miller most wishes to put his stones in order and give them extra work and care. It also necessitates the stones being dressed ou one spot, as well as the erection of driving gear for the purpose ; and whilst not being quite •so dependent on individual skill as with the handbill, a certain amount of skill is indispensable to obtain a uniform depth of the 'tracking, and to prevent the diamond from being broken or injured, as it is very liable to be at the high speed at which it rotates. These defects form the serious drawback from the advantages of this machine, and a hindrance to its more general use. utilised at the outlet Ü. I made the casing Oft. lone by 18in. diameter, of 1 platee. The Internal water coil It was ljin. inside diameter, and about ISft. long before it was coiled. It was a very effective appliance, hen tingthe feed water to within 10° of the steam In the boiler. This arrangement, moreover, permita the pump to bo worked with cold water, which any practical man will see la nn advantage. I shall be happy to furnish detail» on application for my address through the advertisement column. Llah.

There cannot at the present time be the least doubt that the practical success of the mere cutting action in Golay's machine was in reality due to a very great extent to his using, not the diamond, but bort or carbon, of which the special and distinctive properties and peculiar suitability for cutting hard «tono had been previously discovered by .lobin. It was very fortunate for Golay that he met with specimens of bort for his trials, for he would certainly have met with no better or more permanent success than Childs or Dickinson had he had only common glaziers' diamonds to work with.

Popularly the term "diamond," or "black diamond," is applied to the stones used for dressing millstones ; but the term is inaccurate, and bort—which is the substance really used—is not diamond. The diamond properly so called is a crystalline substance with an easy cleavage; and even when reduced to fine dust.'the particles retain their crystalline structure; hence the giittiuess, ¡и which lies the great abrading power of the dust. Bort, on the contrary, is amorphous, or destitute of crystalline structure or cleavage, and its dust, having no grittiness or abrading power, is quite useless to lapidaries. Bort, probably like the diamond, consists mainly of carbon, but in an allotropie or different state. It is very remarkable that the amorphous bort should be harder than the crystalline diamond, bur, so it is, and a good specimen of bort will with a single steady rectilinear stroke cut in atone a groove one-eighth of an inch in depth— work which would be simple destruction to any translucent or crystaline diamond.

We may now compare Golay's vague description of the substances he proposed to me, " hard stones, and especially the diamond," with Jobin's clear aud definite statement published three years before Golay's. In the specification of his patent, to which we have already referred, Jobin

S»V» :—

"The invention consists principally in the use

of the materials or substances called hurt and

carbon, these being employed instead of steel for

the cotters or cutting surfaces or points of the

tools or machines. These substances are well

known to lapidaries, and may be procured from

Brazil and other places were diamonds are found,

being, in fact, rough or impure portions of stone

foutu" ш connection with the diamond; and not

being sufficiently pure te be suitable for jewellery

these subitáneos can be used with economy and

advantage. Bort or carbon are extremely hard,

and not capable of being drilled on the edge or

•worn away by friction with any material but

themselves."

The success of Golay's machino was not at first attributed to the kind of stone, but to his peculiar and very ingenious rotatory chipping action, and it was at one time thought that that

action was absolutely essential to success. It is clear, from Golay's specification, that this was his own opinion ; and it was owing to this belief that so large a sum as £200,000 was so soon invested in the patent.

The first to put forward any plan in competition with Golay's was Robert Young, an engineer and experienced maker of machinery specially for millers. It was not, however, Goby's success which first drew his attention to the matter, for iu 1Я62, when Knight's patent was obtained, he had received one of Knight's machines from America, and had endeavoured to obtain its adoption by several millers in Scotland, but found that the expense of the diamond was objected to; and he was then unaware of the existence of the not only less expensive, but also more suitable bore. Though discouraged, Young himself sttll remained convinced of the desirabily of a millstone dressing machine, and never abandoned the idea of producing a successful one. He did not see why a plain rectilinear cut with the diamond, such as had been proposed long before by Childs, should not answer as well as the rotatory chipping, if suitable arrangements were made ior its application, lie designed various modifications of apparatus for carrying "fit his views, and took out a patent on February 12th, 18G8, No. 47Ô, the mere title of which showed that he aimed at things beyond what Glay had contemplated, it being "Improvements in apparatus for training, levelling, and dressing millstones." Careful observation and experiment soon led Mr. Young to see that the quality of the diamond or cutting material had an important bearing on the matter, and that, in fact, when bort was used the excessively rapid power-using rotatory clipping action introduced by M. G lay was an altogether unnecessary addition. Mr. Young's study of the subject resulted in the principles that in order to make bort act satisfactorily with the simple rectilinear cut like that of the tool of an ordinary planing machine, it must be held in a slide guided firmly and steadily, so as to move accurately in a straight line, and be unable to deviate therefrom either upwards or laterally, and that to meet the inequalities and varying hardness of the burr stone composing the millstone face, the bort should not be held with absolute rigidity, but so as to have an extremely slight elasticity. Whilst designing his apparatus in accordance with these principles, he further arranged it so as not only to maintain the truth and level of the stone, but also so as to gradually correct any departure therefrom. The patent already referred to and a more recent one, comprise various modifications of Mr. Young's apparatus, but the following is a description of the ono which he finds best adapted to the various practical requirements.

(To be continued.')

A GOOD PAINT. Mrs would direct the attention of those de"" eirous of trying good paint to the sorts manufactured by "Jay's Metallic Paint Company," of the Woodham Works, near Vauxhall .Station. It is very cheap, not only in its first cost, but in the economy of its use, one coating being equal to two of any other paint, according to the inventor. The chief merit of the invention is in the utilisation of the common resin of commerce in combination with oxide of zinc. The resin is first broken up into dust or small pieces, and then dissolved in benzoline or turpentine until the solution acquires the consistency of syrup or treacle, or equal parts of each of the above spirits or hydrocarbons, and any other hydrocarbon that will dry and combine with drying oils can be used instead of turpentine or benzoline. When the solution is complete it is gradually added to the oxide of zinc, which has previously been made into a paste with boiled linseed oil, until the whole mixture acquires the consistency of paint suitable for use. A white paint is thus produced of a most durable and glossy character, capable of resisting heat, moisture, cold, and friction better tlian: any other known paint. Other pigments, such as sulphate of barytes, oxide of iron, Brunswick green, red lead, or any other known ingredient, can be added to make any desired colour of paint. One great advantage of its use is its effectual resistance to boat and moisture. It never blisters or cracks, even under the hottest sun or the most inclement weather.

ON AN APLANATIC SEARCHER. AND ITS EFFECTS IN IMPROVING HIGH-POWER DEFINITION IN THE MICROSCOPE.*

ГГШЕ Aplanatic Searcher described by Dr. JL Pigott is intended to improve the penetration, amplify magnifying power, intensify definition, and raise the objective somewhat* further from its dangerous proximity the delicate co vering-gluss indispensable to the observation of objects under very high powers.

The inquiry into the practicability of improving the performance of microscopic object-glasses of the very finest known quality was suggested by an accidental resolution in 1862 of the Podura markings into black beads. This led to a search for the cause of defective definition, if any existed. A variety of first-class objectives, from

tho — to the \, failed to show the beading, al

16 though most carefully constructed by Messrs. Powell and Zealand.

Experiments having been instituted on tho nature of the errors, it was found that the ¡LStrument required abetter distribution of power ; instead of depending upon the deepest eyepieces and most powerful objectives hitherto constructed, that better effects could be produced by regulating a more gradual bending or contraction of the eccentrical rays emauuting from a brilliant microscopic origin of light.

It then appeared that delusive images, which the writer has ventured to name eiJola* exist in close proximity to the best focal point, (where the least circle of confusion finds its locus).

(L) That these images, possessing extraordinary characters, exist principally above or below the best focal point, according as the objective spherical aberration is positive or negative.

(II.) That test-images may be formed of a high order of delicacy and accurate portraiture, in miniature, by employing an objective of twice tho focal depth, or, rather, half the focal length of the observing objective.

(III.) That such test-images (which may be obtained conveniently two thousand times less than a blown original) are formed (under precautions) with u remarkable freedom from aberration, which appears to be reduced in the miuiature to a minimum.

(IV.) The beauty or indistinctness with which they are displayed (especially on the immersion system) is a marvellous test of the correction of the observing objective but an indifferent one of the image-forming objective used to produce the testing miuiature.

These results enable the observer to compare the known with unknown. By observing a variety of brilliant images of known objects, as gauze, lace, an ivory thermometer, and sparkles of mercury, all formed in the focus of the objective, to be tested with the microscope properly adjusted, so that the axes of the two objectives may be coincident, and their corrections suitably manipulated, it is practicable to compare known delusions with suspected phenomena.

It was then observed (by means of such appliances) that the aberration developed by high- power eyepieces aud a lougthenod tube, followed a peculiar law.

A. A lengthened tubo incroased aberration faster than it gained power (roughly the aberration varied as r-, while the power varied as r).

B. As the image was formed by the objective at points nearer to it than the standard distance of 9in., for which the best English glasses are corrected, the writer found the aberration diminished faster than the power was lost, by shortening the body of the instrument.

C. The aberration became negatively affected, and required a positive compensation.

D. Frequent consideration of the equations for aplanatism. suggested the idea of searching the axis of the instrument for aplanatic foci, and that many such foci would probably be found to exist in proportion to the number of terms in the equations (involving curvatures and positions).

E. The law was then ascertained that power could be raised, and definition intensified, by positively correcting the searching lenses in proportion as they approached the objective, at the same time applying a similar correction to the observing objective.

The chief results hitherto obtained may be thus summarised :—

• By C. W. Гиютт, M.A., and read before the lioyft( Socteiy. * гто.а ti'e'wXo»', a frd*c spectral ira ige.

Tie writer measured the distance gained by the nj lunatic searcher, whilst observing with a 4* in. oljective with a power of seven hundred

2 diameters, and found it — of an inch increase ; so

10 that optical penetration was attainable with this high power through plate-glass nearly i'ra. thick, whilst, visual focal depth was proportionally increased.

The aplanatic searcher increases the power of the microscope from two and a half to five times the usual power obtained with a third or C eyepiece of lin. focal length. The J thus acquires

the power of a —, the penetration of a J. And

25 at the same time the lowest possible eyepiece (3in. foens) is substituted for the deep eyepiece formed of minute lenses, and guarded with a minutely perforated cap. The writer lately exhibited to Messrs. Powell and Lealand a brilliant definition, under a power of 4000 diameters, with their new "I immersion" lens, by means of the searcher and low eyepiece.

The traverse of the aplanatic searcher introduces remarkable chromatic corrections, displayed in the unexpected colouring developed in microscopic test objects.*

The siogular properties, or rather phenomena, shown by eidola, enable the practised observer in many cases to distinguish between true and delusive appearsneof, especially when aided by the aberrameter applied to the objective to display eccentrical aberration by cutting off eccentrical says.

Eidola are symmetrically placed on each sido of the best focal point, as ascertained by the aberrameter when the compensationshave attained a delicate balance of opposite corrections.

If the beading, for instance, of a test-object exists in two contiguous parallel planes, the eidola of one set is commingled with the true image of the other. But the upper or lower set may be separately displayed, either by depressing the false eidoia of the lower stratum, or elevating the eidola of the upper. For when the eidola of two contiguous strata are intermingled, correct definition is impossible so long as the aperture of the objective remains considerable.

One other result accrues: when an objective, otherwise excellent, cannot be further corrected, the component glasses being already closely screwed up together, a further correction can be applied by means of the adjustments of the aplanatic searcher itBelf, all of which are essentially conjugate with the actions of the objective and the variable positions of its component lenses; so that if Ix be the traversing movements of the objective lenses, on that of the searcher, F the focal distance of the image from the objective when dx vanishes, f the focal distance of the virtual image formed by the facet lenses of the objective,

Ob ,Y'

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The appendix refers to plates illustrating the mechanical arrangements for the discrimination of the eidola and true images, and for traversing the lenses of the aplanatic seareher.

The plates which the author supplied with the paper also showed the course of the optical pencils, spurious discs of residuary aberration and imperfect definition, as well as some examples of •'high power resolution" of the Podura and LepUma beading, as well as the amount of amplification obtained by camera-lucida outline drawings of a given scale.

AN IMPROVEMENT IN FILTRATION. By Pro*. Joiin C. Gilbert, M.d.,nkw York College^

To those who hare been unnblc to employ Hansen's improvement in filtration became of an insufficient supply of water to produce the neceeury exhaustion, it may be of interest to know that all the practical adiantages may be obtained by means of a simple and inexpeuBive apparatus, which it is the object of this communication to describe.

The u]i|)iirHtua consists of a stout boiler a, with three openings 'iirroritioodating respectively a pressme-gaure b, ;. supply-funnel < for the introduction of water, and a tube U connecting with the exhausting arrangement or steam vacuum-tube e, represented in section at /, in which / ia a brass or glass tube £ an inch in diameter, terminating in a

mall conical opening or nozzle — of an inch in diameter. 32

* Alluded to by Mr. Rende, F.R.S., in "Popular Science Review " for April, 1870.

t Communicated by the author to the "Philosophical Magazine."

In the interior of/ and passing air-tight through the stuffing box A, there is a, similar tube g about Jin. in diameter

and terminating in a nozzle or opening like /, and about —

04 of an inch in diameter. At k a tube £in. in diameter opens into/.

The nozzle-tubes/, gbeing placed in position as shown in the figure, steam is raised to the boiler a .- this passing through the tube dr. to y, issues with violence from the nozzle; and in passing through the nozzle of/ produces an exhaustion in the interior of the tube / which may be ap

[graphic]

plied as desired by a flexible tube attached to k. The vacuum produced depends partly on the shape of the nozzles, and partly on their relative position. The latter adjustment is obtained by slipping the tube g through the stuffing-box h until the proper position is found, lu the arrangement employed by me, I nave without difficulty obtained with a pressure of one atmosphere of steam iu the boiler an exhaustion capable of raising mercory Bin. perpendicularly in a tube attached to k, the exhaustion increasing steadily aa the pressure uf the steam increased.

At / m. the filtering-apparatus is represented as attached to the steam vacuum-tube / by the flexible india-rubber connector n.

THE EXGLISH MECHANIC SOCIETY OF ARTS. (edinburgh Branch.)

In accordance with the advertisements in the English Mechanic of April 22nd and 29th, a number of its subscribers .met in the Waverley Hotel on the evening of the 20th. Being unanimously of opinion that the formation of a society, having in view the aims and objects spoken of by several correspondents in our pages, they appointed a chairman, and at ence proceeded to give themselves a name.

After a pretty sharp discussion (iu the course of which Mr. Kemp—the originator of the idea—took occasion to point out specifically the advantages to be derived by the members meeting together), the name given above was agreed upon. It was then decided that the meetings should be held on the first Thursday of every month, commencing on Thursday, May 5th, at 8.15 p.m. A committee of seven was appointed to draught out rules and bye-laws for the guidance of the members; as a mark of esteem it was decided to elect Mr. J. Passmore Edwards, Honorary President.

A very general and decided expression of opinion was given concerning the very great improvement recently effected in the English Mechanic, and a cordial vote of thanks was passed to the Editor for bis efforts in that direction.

The thanks of the members having been awarded to Mr. Kemp as the founder of the fabric, the customary vote to the chairman closed the proceeding!*

The committee met on Monday, May 2, at 8.30 p.m., when the following among other rules were agreed to :—

1. No party, political, nor sectarian religious subject shall be discussed at the meetings.

2. The meeting shall be opened by one of the members reading an essay (original, we presume, but not so specified], not more than 15 minutes In length. The discussion nristng thereon to be finished not later than 9*20 p.m., the remainder of the evening to be devoted to asking and unswering questions on any subject in which any of the members may be interested. C. E. Gordon, Interim. Sec.

MATHEMATICS.

By C. H. W. Bigg».

CHAPTER lU.~(CoHthkwrd.)

Decimals.

(CotUinued from page 83.)

4 37. If the denominator of any fraction be 10; or some power of 10, it can be immediately written as a decimal. but if the denominator be 4, 5, 6, &c., it may or may not be capable of being exactly expressed ns a decimal. For all practical purposes, however, the difference between the fraction expressed by either method is too little to be considered.

Thup a \ - -3333333, ad infinitum.

0 * = ■»■

In a* w- have a decimal answering nearly to the vulgar

fraction.

R m exactly

i fraction.

Decimals of the former kind, whentlie figures are repealed

I over and over again, are termed circrUn'.iiii, repenting, or recurring decimals, and the part repeated is called the period or repeiend. The method of transposing it vulgar into a decimal fraction is to divide the numerator by the denominator, adding noughts to the former us required. Thus 31 — = 10J; 10 remaining in both cases as a whole number,

o\vooOOO

and = 10 3338, Sec. To facilitate calculations,*

■33333, fcc., dot is generally placed over the fnurc or figures rcpentod, instead of writing down the figures over and over agitin.

Thus : "'3 = -33S3, &£., and "57 = 575757, See., and -31*7 = -31473147, Sic When the figures recur immediately after the decimal point we get a pvrc circulator; nil other periods are called mixed.

* 38. From what has already been said, it appears that the methods of calculation wherein decimals are introduced, cannot in the slightest degree differ from those or couuuun arithmetic; and that the only matter involving any dimculty is the determination of the limit where a product or quotient is made up of an integral or decimal series, or of both combined. The rules for this determination are simple* and can be easily understood, as will be seen iu the following paragraphs.

i 39. Addition.—In adding vulgar fractions we reduced the fractions to a contnum denomination, and then the sum of the numerators gave the required result. But in decimals we have the numerators alone expressed, aud the unexpressed denominators are easily made ajmrnon by the mere arrangement of the figures in a certain order. Thus in K series of decimal fractions whose sum is to be obtained, since the first place of decimals in each of the numbers is the place of the tenth, the in of all the ^digital occupying that

Elace is the sum of the numerators of a series of fractions aving the common denominator ten; the sum of the digits in tho second place will be the sum of the numerators of. a series of fractions with the common denominator 100; and so on. If, therefore, the given series of numbers is so written one below another that the decimal points arc in one r^rtiaai column, then the digits in every column will be the numerators of fractions with toe same denominator; further, if theiiim of the Second column be ten—i.e., ten onc-fam10

dredths we may substitute one-tenth, i.e., nnc

100 unit of the first column in its stead, and generally we majcarry from column to column in the decimal parts the same as in the whole numbers. _ ,

Ex. Addtogether2S; 46; 167; Hl'l and 863 2. Writing these numbers so that the decimal points are in one vertical column, we have

2-3 \ or by neglecting for a moment the m40 ) tegers we may write:—

16 7

1 S 5 7 1 2 18 8

141-1 J — +—+—+—+—=— or 1>—

by adding as 363-2) 10 10 IU 10 10 10 10

in whole Nos.

we get 527-8

Now adding the integers we get 526, to which add

8 8

making ns before 527—, for -8 = —
10 10

Ex. Add together 3140-7864, -0003, 70 3350 and 89WM26.
As before set down thus-.—
Syfia

4 + 2 + 6 + 6 18

3149 7 8 C 4 or a = =

10000 10O0O

10 + 8 1 6

• 0 0 0 2 = = +

10000 1000 lOtOO

1

79- 3 8 5 6 in practice we carry to

1000 8940- 0 12 6 R, setting down 8 under a. and so

Adding 0+6 + 2

we get 12169 18 4 8 on, for we have: , add to

this 1000

6 + 5+2 1 14

in R + carried as above =

1000 1000 MOtt

10 + 4 1 4

THE MANCHESTRIAN EXGLISH MECHANICS MUTUAL IMPROVEMENT SOCIETY. In accordance with the advertisement in last week's issue of the English Mf.chanic some of its subscribers living in Manchester assembled on Friday, the 29th of April, at the Dog and Partridge Hotel, Corporation-street. Mr. A. Tolhausen gave an address on the propriety of forming such a society, and tho advantages likely to be derived from it. After speeches from Mr. Rees, Mr. Tweedale, and Mr. Bsguley on the formation of the society, it was determined to meet again at 8 o'clock p.m., on Monday, the 16th of May, to enrol members, to appoint officers, and to elect Mr. Tolhausen as the hon. secretary.

10

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Obs. That every series of figures in which no decimal point is expressed is conceived to have one affixed to the last figure oo the right, and that cyphers may be added beyond this limit, from which the decimals are to be deducted.

Ex. 11 Subtract.

(1.) 724316 from 815472.

(2.) 3272 from 187*64159.

(3.) From 29715 take "209176.

(4.) 310*27 — 691425 and 63 — 1*4709.

(5.) Find the difference between 20 and '02.

(6.) Between 17564 and 176 64; also between 17564 and 17564.

§ 41. Multiplication.— To multiply any decimal by ten. one hundred, one thousand, See, we have simply to move the decimal point one, two, or three places respectively to the right, from

2315

2.S45 x 10 = x 10

1000

SMS

= = 23-45

100 2345

2-S45 x 100 = . x 100

iooo
2345

= = 2345, and soon.

10 § 42. To multiply by any number. Place the multiplier under the multiplicand as in common arithmetic, and proceed as usual, observing to cut off as many figures in the product for decimals as there are figures of this denomination in both the multiplier and multiplicand together. Ex. Multiply 314 16 by 32406.

31410 Here we have tire decimals
32406 „ four

Total six

Therefore in product mark off sick figures

as decimals from the right.

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i 43. The proof of the rule by which we are directed to cut off as many decimal places in the product as there are together in the multiplier and multiplicand may thus be shown:—

1x1 = 1 10 x 10 = 100 100 x 100 = 10000 By the examination of which results, as it appears that a multiplier and multiplicand, containing each three figures, are necessary to yield a product which is the smallest integral expression that can be given with five places of figures, so tliat it is conclusively apparent that no more than four places of figures cm result from the multiplication of the two largest integral expressions that can be afforded with two places of figures. We know, moreover,that unity multiplied by unity only produces unity, and therefore that the multiplication of the two largest decimal expressions that can be formed, will never yield a product as large, which must consequently be a purely decimal series. Again, the expression *1 is the smallest decimal that can be written where one place of figures only is employed, and this decimal multiplied by unity still gives a product no greater; therefore, if it be multiplied by another decimal, the largest that can be expressed in one place of figures, it must yield a product less than that which was shown to be the smallest decimal expressible by one place of figures, which product must necessarily, on this account, have two places of decimals. Hence the rule is rendered conclusive. Accordingly, when the product yields fewer places of figures than there are in the multiplier and multiplicand together, cyphers must be prefixed to the left hand of the result, till* the required conditions are fulfilled.

•1 ■9 Ex. "1 x *9 = —, but the total number of decimals in •9 the answer must be two, therefore we prefix 0, and write 09. Ex. IS. Multiply by ten:— (l.j 1-073,66 3 40.-087. 113*2676, 14*364. (9.) By ahundred, 345-921,67-341, 427-614* (3.) By ten thousand, 310097, 610*41263, S10096. Find the product of:— (4.) 120*5 x 4176,375-4 x -057. («0 0001 x *001, 321 x 2-31.

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THE USES AND VALUE OF SALT. A Correspondent of the Illustrated Fhvtogrtrpher, having noticed some recent communications on the subject of salt as an article of diet, sends the following remarks thereon i—A really heavy tax on salt is the cruellest impost that can afllict a nation. The first settlers of a colony have described the want of salt as a most severe privation, and stated that the arrival of red-herring, salt cod, or stockfish, has been hailed with public rejoicing. Salt is good for man and beast For our useful allies, the ruminants, salt is the first condition of health and vigour, and succulence. The experience of most farmers will show the benefit derived from mixing salt with the food of cattle. It appears to be the natural and universal stimulus to the digestive organs, and frequently recalls the appetite more speedily than any other stomachic. It is, besides, a or, which, with cattle, very seldom fails. It promotes the condition of sheep when occasionally sprinkled over their food or placed within their reach. It is the basis of nearly every medicine which has real power over their disease, the rot; and it has often completely arrested its fatal progress. Coarse salt herhage growing near the sea is preferred by cattle to the fattest pasture of the interior, and in many markets the highest price is given for mutton fed in salt marshes or meadows. It was said by One who spake as never man spake, " Ye are the salt of the earth." Salt is a pledge of hospitality. The Arab feels bound to protect and shelter the stranger who has tasted salt beneath his tent. Salt is eminently the element of salubrity and preservation. The household article most highly valued by people living at great distances from the sea is salt. In besieged cities, the commodity whose price rises quickest is salt. Salt is the principle of growth and vigour. Man's stature and strength are said to be in proportion to the salt he consumes. The ratagoniana and Otaheitans, the tallest of men, use, or used to use, sea water for cooking their food. The Britons, who live in a saline atmosphere, are the most hairy race of mankind in Europe. Repairers and beautifiersof ladies and gentlemen are advised to note this remarkable fact. Without salt, men could not preserve the provisions, fish and meat, which they have obtained by their toil and industrv. Deprive men of salt, condemn them to eat unsalted food, and they soon become infested with all sorts of parasitic vermin. The Abyssinians, who eat much meat, and have no salt, are generally afUieted with tape worms. It is recorded in some book that amongst certain Northern nations the interdiction of salt was the capital punishment reserved for the aristocracy. After weeks or months of a ashless regimen, the culprit sank under the attacks of innumerable parasites. North American stags traverse immense distances for the sake of drinking at saline springs; instinct or family tradition has taught them that it is the only means of getting rid of the ticks with which they become infested while browsing in the woods. Pigeons are passionately fond of salt. There are sundry recipes, some not too cleanly, not only to keep them from deserting their dove-cote, but to entice and retain vagaboud and wandering

}>igeons. There is the bit of salt cod, the roast joint of pickled ox, the lump of clay kneaded with brine and aromatic seeds; but, in all, it is the salt which is the real attraction. Pigeons peck at walls, as goats and sheep lick them, to obtain the saltpetre which sometimes effloresces on their surface, llces are fond of drinking water decidedly charged with saline elements.

LETTERS TO THE EDITOR.

[We do not hold ourselves responsible for the opinions of otr correspondents. The Koitor reepectfully requests that all communications Should be drawn up as briefly as possible.]

*»* All communications should be addressed to the Editor of the -R, Mechanic, 81, Tavistockstreet, Coven*. Garden, W.C.

All eheques and Foot Office Orders to be made payable to J. Tassmore Kdwards.

i would have every one write what he knows, and as much as he knows, but no more; and that not In this only, but in all other subjects ■ For such a person may have some particular knowledge and experience *-f the nature of such a person or such a forcetain, that, as to other things, knows no more than what everybody does, and yet to keep a clutter with this little pittance of his, will undertake to write the whole body of physics : a vice from whence threat inconveniences derive their original. — Montaigne's Essays.

CONTACT BREAKER.

Sir,—I cannot say where you can get RhumkorfTs breaker in England. Any optician that has foreign connections can procure it for you. Stcehrer, in Dresden, I believe is where the one I had was procured. The price was £2; but with patience you may make one yourself. The simplest form I here annex, but it will hardly do if you want to go io for experimenting- I will send Rhumkorff'B to the Editor next week. A brass block e contains a rack c and pinion worked by the milled head/. The bead of the rack carries a well hammered brass spring y, about 2 or'i\ centimetres broad, upon which a copper rod K rests, carrying at one end the armature G, and at the other two platinum pendant wires d d (if ID sufficient if about Jin. of the bottom end only be of platinum). The head of the spring g carries also a stout brass wire h, on which a ball C can be raised or lowered -, also the saddle k>\ The ball serves to regu

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late the speed of the instrument. The saddle also car? be moved about to regulate the balancing of the beam. me and Bare the two mercury cups—glass with hard varnished wood bottoms—which are adjustable on the brass screws o o, which go through Into the mercury bb; on the mercury is some good alcohol a ct. The rack is for adjusting the distance of the anchor from the electro-magnet u t and /rare the two binding screws for the inducing current, and / and m for the battery that works the Instrument (a single Grove with 6* by 4'platinum answers very well). A is therefore the breaking cup for the induction curroo*, and B for the breaker working current. If the Instrument In quick the alcohol is very easily thrown out; which i* prevented by the wooden covers, which have a slst running from the centre hole to the circumference to allow of their belugtaken on or off. When standing, the plate let should not touch the quicksilver. and all the connections should be made, and the Instm ment then started by a slight inclination of the wire s with a glass rod. In the tame manner it is stopped beholding the wire still. The greatest power is obtained when the instrument Is worked, so that the time the current is closed is longer than the time during which it is open. This is the same principle asKbumkorff'h, but much simpler. Any other information that lies in my power I will gladly give. Tangent.

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TO MILLERS.

Sib,—1 bow in submission to your judgment in respect to some remarks which I have made in relation to м>ше statements in Mr. Kharpc'e letter. I could not help smiling when Г saw that my letter had made its appearance in public, with both its bead and tail severed from the body. Rather keen treatment this.

It does one's heart good to be told of one's faults or weak point*. Mali generally is blind to these in hitr> >elt; and he is a friend indeed who has the courage to eome forward and point them out; though this may be at times rather trying to proud humanity, never- j theless it may have a vt-ry salutary effect upoo the' patient; and I hope that I am to-day a better and ¡ wiser subject ou account of this correspondence with my dusty brethren. And I hope also that others have proflted something from the hints thrown out by -various correspondents upon this most important branch of industry.

"A Stoneman" still adheres to his text about millstone balancing, and I am glad to find that what he Rays is <he result of practical experience; so also is mine, and fact* are stubborn thiuirs. Hut while looking at both In the face I must acknowledge that he has arrived at a greater degree of perfection than I have, and am afraid ever shall; but am opeu to conviction. He says that he has had considerable experience as a mill-tone builder, und Is slightly acquainted with what eompoees a millstone, &c. lie will probably allow others also to know a little about this, though not to the same practical extent, yet sufficient to give an opinion, which is also the result of much thought and experience. He asks why ehould a stone's standing balance become disturbed when running? An answer to this has been attempted before; but further, the reason in my opinion is simply because the balance weight does not coincido with its counteracting object in its radial distance from the centre. And to illustrate what I say. may I kindly ask him to *ay whether by the aid of Clarke and Dunham's patent balance he cannot dliturb the standing balance when ruunlng by lowering or raising the weight I Let mc also remind my friend that 1 did not say that a true und level bedstone wns not essential to a standing balance, because I considera standing balance virtually of no use and practically non-effective. Let me also remind him that I did not mean to convey the idea, *' the faster the stone runs the greater tendency It ehould have to «»equalise its gravitation." What I meant to convey was, that it would drag even at Its greatest velocity. If he will be kind enough to refer to my letter, I think ho will find this to be correct.

I desire here to say that I am far from considering

II A Stoneman " ignorant or unpractical, but far other* wise, and thank him personally for bis opinion.

Thos. Evans.

Sib,—I read in your journal with plcasnre the remarks of your correspondents on millstone balances. There is evidently a great difference of opinion as to the merits of the running balances. I confess I cannot see what use they arc. I maintain that if you keep your stone ргорет1у balanced when standing, and with a good face and nicely dressed (so that It may carry a good feed), and last, but not least, keep your driver right, you have no need to bother yourself about expensive patent balances. Of course these remarks may be much criticised, but it is the result of many years' experience aud study.

Millstones, like other things, differ in their nature, and it would be idle to deliue a certain mode of dressing them; this is entirely left to the judgment and common sense of the stoneman, who alone can make them work as they should. I may mention here that I have a stone that will run empty as well as grinding, and it works no better than any oue in the mill. I perfectly understand what running balances are designed to do, and would fully appreciate their good services (if any), yet up to the present time I am at a loss to understand why practical millers bhould value them so highly.

I should be glad to hear mere under the above heading from your-readers, and «specially about silk dressing machines. J. tí.

Sir,—Your correspondent "A Stoneman " says he bus asked many millers for their opinion on millstone balancing, but till now could get no direct reply.

I am not surprised at that being tho result of his inquiry, but I think If he studies ihe information that is to be obtained in the pages of the English MeChanic, he will soon be able to give a direct answer to any one who asks his »pinion, and will also see the value of "science combined with practice," but he must have patience if all at once he cannot understand how the unequal density of the materials of which a millstone is composed is acted upon when rapid motion converts gravity into centrifugal force, but the same laws govern the motion of the millstone :ts hold the world In its orbit round the sun since its first being launched forth into space. In these pages we have tho scientific freely Imparting their learning, and in turn asking questions of the practical workman. Such a bond of brotherhood the world of literature has never before seen. Other papers, seeing the success of tho English Mechanic, are playing "second fiddle." but to the English Mechanic must be awarded the leadership, and the results must have far exceeded the most sanguine anticipations of the proprietor—but I have no business to wander from my subject in hand, as I generally try to write only what 1 know to be of practical value, but just this once I trust our Editor will allow me to scribble upon what I know but little about. I sou a " Clerical Cor

respondent " rather out of his depth when be recommeuds working steam engines by clockwork, instead of coals, nnd J think that by admitting such letters as John llearsley's. page l'H, "the Kncmsii Mechanic. does good, as harm would bo done if they were excluded, for many of those who have valuable practical knowledge, are {«»completely ignorant of all scientific method, that they do not even know of its existence, but I íeel sure the corr?spondent " A Stoneman," for whose benefit I now write, will not remain one of this class, but will endeavour to combine the pleasure and advantage of scientific and practical knowledge which Is necessary to understand the balancing of a millstone in motiou, U. il. Smith.

THE EARTH'S FOHM.

Sib,—Last week I had something to say to Mr. Iteardsley, this time Г will try to entertain your readers with some astounding stuff published by Mr. Hampden, one of ** Parallax's " apostk-s. This is the person who recently proved his faith and his folly by staking £f>00 on the question whether the earth is round or flat. île has published a pamphlet, "God's Truth or Man's Science, Which shall Prevail?" God's truth has no enemy more deadly than the man who sets it up as something opposed to man's science, for man's science, based on facts, is sure to prêtait, and thus contempt is thrown on God's real truth by its supposed association with proved error. The most remarkable thing about the.*© people, is the cool way in which they inisconstrne scientific opinions, aud stick up a muii of straw for the purpose of knocking it down, and then triumphing la their victory. Thus; Mr. Ilumpiu describes two vessels leaving land, one going out till "all bat her mizen niants will Iv.ivr. vanished (whatever this may mean 1 cannot say); the second, till "just as she appears to be on tho crest of the horizon." and both brought to a stand still; the spectators now go to this last, where they "expect to sec the fir.it with their topmasts ou a level with tho decks of the vessel on which they are standing, and they themselves considerably overtopping the level of the coast from which they started." They would expect nothing of the kind if they held the true scientific opinions. "Lut, oh, their dismay at finding themselves in an apparent hollow, and both tho vessel ahead, and the houses on shore, at a considerable elevation above them." They would fiud nothing of the kind. This miserable farrago is set forth as facta and argument. Surely it would have paid Mr. Hampden lo have gone, say over to Calais, before staking his moaey, he would then have seen what realiy does occur.

The trial made was this; three marks were fixed at the same height above tho water, at distauces, I believe, three milts apart, and a telescope at either eud, showed the middle one some feet above the straight line joining the two end one¡», as of cour.-o it must, nwioe to the curve of the earth. Furious at this, the wiseacres now fall back on the ordinary effect of distance or perspective, which hoe «o effect on a ttrait/ht line nt the level of the eye, ан iu this case. Unable to comprehend the simple fact, they assert that the scientific view of this means that in the fir^t distance there is a rise followed by a fall, whereas the simple fact is, that a telescope 1er МЫ truly, would ¡it any station point considerably above any object at the same height as itself from the water; thus Mr. 11., after showing the fall the curve would appear to produce, triumphantly exclaims, " But mnrk, when they get to the end they will be required to retrace their steps, and show this time a rise, where they showed a fall.*' His mind cannot couccive the curve, or the simplest principles of the spherical doe tri tie. In his wrath he published another pamphlet,'"The Bedford ('anal Swindle Detected and Exposed," and I will furnish a few extracts, which will show clearly the remarkable seu&e, honourable feeling, and Christian charity of this wonderful champion of "Truth."

"Mr. Hampden took up tho subject, simply and solely relying on the fact, that the Bible, or Scriptural evidence, as far as it went, uniformly ignored, if it did not directly oppose, the notion of a globular earth." Simply enough, goodness knows; on the same grounds we may as well deny the existence of the electric 1 olograph and the steam engine. I am pretty well versed in Scripture, and to the best of my knowledge, ft very thoroughly ignores, "if it doea not directly oppose " (as ir might, very easily be twisted into doing) these samples of man's science, Havin/ issued his challenge, he says. " ¡>o little confidence did the protended philosophers and engineers feel In their theory, that it was not till several weeks that a solitary reply was triveu to this challenge." Of course not; it was looked upon as a "skit ;"' no one supposed that there was any one sufficiently foolish to have meant It, and few true men of science would condescend to literally plunder the poor creature. Here Is charity: "If there is one class of men, next to horse dealers and jockeys, who bear the unenviable reputation of being the most tricky and unscrupulous in their assertions, it is the members of our scientific societies; to nothing but their unscrupulous falsehoods and boldness of assertion, are the astronomers and philosophers indebted for much of tho reputation they possess." "Knaves and liars," aud so forth, are abundantly scattered; "the cowardice of the scientific world equal to its knavery;" "shifty, doJgy," &c, one meets every other line, and all this from a man whose sense of truth is во weak, or his knowledge so profoundly little, that he has the assurance to say, " they have never made a single experiment, the truth of which can be iucontestably proved, and they stick to their insane theory because it is ingenious." All this, too, about men who spend their lives in experiment, and who deem their greatest triumph, the finding something new, never hesitating to attack each other, and about doctrines mixed up with all our knowledge and all the commonest affairs of life, and so brought to hourly tests.

There is just one line of truth In the two pamphlets. "One einglo proof would be worth a thousand mere assertions." Will Mr. H. just take that oue piece of truth to hN own heart? One rag of an argument this

Îious philosopher gives. "If, while prayiag to our 'ather who is In heaven, during the day, we should rabo our hands aud eyes towards the sky over our heads, we must, when similarly engaged during the

hours of night, direct our eyes and thoughts to a spot down through the floor or over the side of our bed. It Is no joke, this is the positive fnct." N.B.—These last word- are part of the extract ; please repeat them and continue. This miserable twaddle Is actually offered as an argument on n scientific subject. Does Mr. 11. suppose the Iьfinite Father is In the sun only, or what does he mean by insulting our common sense. Then for honesty, " aud МЮ men In a thousand, in the possession of their sense», believe these villanous assertions of less than lui(f a dozen infidel philosopher*. without one atom more proof than they have tor believing that every house in London was built by the fairies." This is of what the whole educated world knows to be proved and tested truth

When gentry like Messrs. Hampden and Beards ley have answered the simple facts set forth in my last letter, page Ш, It will be time enough to answer their objections as to what may, might, could, would, or should result from the theory of the earth's globular form. Sigma.

PHOTOGUAPHIC.

Sib,—Under the column "Useful and Scientific Notes," nnd the heading " Something New on Silvering Paper," I read something that I would wb>u our readers and others to especially avoid.

In my former letters on "Printing," Г advised the drawing of the paper over a glass rod ¡it the end of tho dish—i.e., for small pieces ot paper, on no account for large. Now a glass rod is more easily kept clean, or cleaned at any time, than the side of a dish is, coosequently we run less risk of soiling the paper. So mucb for the first part of the article. Now tor the blottiDj. paper part—DJ all noans Khun that. I once tried it, —the result was (.lull prints. 'Now, what can be worse than a dull print? Besides that, there is a grave fault with the blotting-paper. As you place sheet after sheet of seusltive taper, the blotting-paper absorbs the moisture, and of course it goes on the back of the next sheet; the consequence is. your silver goes into the paper. That is what makes the dull print. If it were not to prevent the silver from going into the paper we should float longer. I have proved, and сап still prove, what I say to be true.

I sincerely hope that our photographic friends will not try it. Better waste a drop or two of solution than turn out bad prints. Let us not be contented with inferior work, There's no medium; a thing is eithergood or bad, and, above all, let us avoid rushing madly at every new "dodge" that turns up. When you have good work, be satisfied.

Photography is au "art-scionce,"and we saoo/d do all iu our power to promote au-i ¿how forth the art qualities of it, Wuli a little саге aud study it Is just as easy to take a landscape or a portrait In an artistic manner as in an (»artistic one. Apropoè of art, photographers aud other artists will do', well to read Mr. Hubináou's work on " Pictorial Kfftct in Photography."

Mrs.

P. S.—I have tried that method of taking stereo» ot busts, «be, mentioned a week or two ago, ааЛ tmi it answers very well. I will enclose one later, thai you may judge for yourself.

Mli. VIVIAN'S R.EFLY TO " F.B.À.S."

Sir,—Anyone reading that part of *' F.Il A.s.v letter which refers to mine (p. \V», might imagine that my calculation i.s Incorrect, which I must dcuy. The rule he states ce-taluly does give the focus of a crossed lens, but it is the geometrical focus, or such as it would be supposing the refractive index to be unity. Now, as the index can in no rase be unity, of course the rub) given by " F.K.A.S.'* will n»t give a proper rtsult, but if such rule is to be made use of, the result obtained must be diminished by dividing it by a quantity to be arrived at by multiplying the actual refractive index, less unity, by 2, for this case 0*524 x 2 = 1*048. И "F.R.A.S.'s expression be worked out, and the result divided by this number—i.e.,1*018, it will give the true refractei.1 focus, which will be fouud to bo only a very small fraction of au inch more than ¡S2iu.( or fift, loin. 1 may add that I have not attempted an fndependeot cumulation. All that I have done is simply to adapt Hersehcl's curves, given in his work on the telescope, referred to by ** A Fellow of the Koyal Astronomical Society," to the foci referred to by " Neptune," and to offer if that is not sufficient to do more. I do not nute light of the calculation. I shall have to go through it if this is required, though I should have thought that a practical astronomer like our frieud, who must be used to rather long computations, woold nothave made much of lt. Ue.nrt T. ViviAX.

COTTON SPINNING.

Sin,—It is with great satisfaction I see the above important subject receiving cousideration iu y oar columns. Let us hope that every person will write what lie knows, and no more. Let him be sure that what he sends is right before ho communicates it, and bear in mind that wrong ideas on any subject are something liko an infectious disease—v«*ry catching, and sometimes doing much mischief. People generally act practically on the information they receive; a false or thoughtless statement may do mischief to no small amount. The boon you are conferring; upon ns by opening your pages for discusslug matters appertaining tn cotton spinning is great. In the first place. it will afford us that graud privilege which во many of your readers enjoy, the nu-aus of hearing-, or rather reading each other's opinions on various subjects, about which 'as in all other arts or studicb) there is a great difference of opinion. Secondly. It will be the means of showing this branch «if our manufacture iu it■= true light, not ins many suppose) as a *' eta veno use' for human beings, but as a great school, where there i? almost as much to bo learned aiulexptained as there i . lu the Observatory at Greenwich. Thirdly. It with**** hope, be the means oí bringing hundreds of fresh euTJ ecrlbers to this " means of knowledge," for it will bi¡ ply a long-felt want.

"Factory Lad " lust week asks how a draught should be distributed between 1 sets ot rollers.| depends upon circumstances, if his carding

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