Chapter XIV: Letter XIX: gives a definition of the ellipsis, which would be a (8)

Very annoying and even distressing consequences may ensue from any system of treatment where a constant resistance to the muscles of the fore-part of the neck is kept up. A gentleman had for many years worn one of the collars invented by Mr. Chesher; after some time, the muscles of the back became so weak, as to be incapable of supporting the column, while those on the fore-part of the neck were so disproportionately increased in strength, by the constant resistance opposed to them by the strap passing from the suspending rod under the chin, that whenever the strap was loosened, the chin was forcibly drawn towards the chest. As the muscles of the back part of the neck did not offer any counteracting resistance, the [p240] windpipe was now pressed down, or almost doubled itself. As soon as this took place (and it was almost immediate on the attempt to sit up without the collar,) the patient was seized with such a sense of suffocation, as to be obliged to throw himself on his back. As he was able to breathe with ease as he lay on his back, his advisers were led to believe that it was the weight of the head which pressed down the windpipe. To counteract this pressure, various contrivances had been proposed to support the head. Indeed, the patient himself was so convinced, from what he had heard, that it was the weight of the head which pressed down the windpipe, and so alarmed had he become from the certainty of having a fit of suffocation when the head was left unsupported, that there was much difficulty in persuading him to believe that if the head could be made _heavier_, the sense of suffocation would be relieved. He was at length induced, although with great dread of the consequence, to allow about fourteen pounds of shot to be placed on the top of his head. He was very much alarmed, but it was highly gratifying to witness his surprise and pleasure in finding that, instead of his head being weighed down, he could support it, and could breathe with ease while in the upright posture. The following is the principle on which this plan was proposed:—the muscles of the back part of the neck had been brought into such a state, that their ordinary stimulus was not sufficient to excite them to the action necessary to counteract the efforts of those on the fore-part of the neck, which had been evidently increased in strength. The placing a weight on a certain spot on the head formed an additional stimulus to the muscles of the back part of the neck; a fact which the reader may prove by an experiment on himself.

By proceeding on this principle, by combining a variety of exercises, and by gradually diminishing the weight carried on the head, this gentleman was soon able to walk and sit in a state of great comfort, without being obliged to use any artificial support.

It is well known, that the neck-collars support almost the whole weight of the head and shoulders by the strap which passes under the chin. It must also have been observed, that the wearer very frequently pushes down the head against the [p241] chin strap. In this way, the muscles on the fore-part necessarily become stronger, while those of the back, being deprived of their natural stimulus to action, in consequence of the rod superseding their office, become diminished in power. Even were there no change in the degree of strength in the muscles on the fore-part, the head would naturally fall, if the support afforded by the chin strap were removed; but as these muscles are increased in power, while those of the back are diminished, the head must not only fall, but even be pulled down.

However, although the collars and the lead weight, as they are generally used, are not only inefficacious; but even hurtful, they may occasionally be useful in keeping the head in a certain position, after it has been brought to it by such exercises as tend to strengthen those muscles of the back which support the shoulders and head. But the opinions commonly entertained, as to the means of counteracting an habitual stoop, are so erroneous, that even the position of a tailor sitting on his shopboard is better than the plans generally recommended. This at first appears ridiculous; but the manner a tailor holds his body when he walks, proves that there is something in his habits which tends to the correction of a stoop; for he is quite a caricature of a strutting erect figure, especially in the way he bends in his loins and carries his head.

The peculiarity of the tailor’s gait proceeds, in a certain degree, from the bent position in which he sits: but this explanation is not at first satisfactory, since it may be observed that other tradesmen, who also stoop while at work, generally have their head inclined forwards, and have also a distinct and habitual bend in the neck; such, especially, is the condition of persons who sit at a table and stoop forwards, as watchmakers, engravers, &c. It is not difficult to explain the cause of the difference, and the inquiry will assist in directing us to the principles which we ought to recollect in our operations upon the spine.

In the sitting position of the tailor, the head hangs so low, and so complete an arch is formed between it and the pelvis, that the muscles of the spine are called into strong action to support the head; the necessary consequence of this is, that these muscles become even unnaturally strong, or at least so strong as to predominate over those by which the spine is [p242] pulled forward. But the bent position is not the only cause of increase in the strength of the muscles, for it depends also on the exercise given by frequently jerking the head backwards. In those who stoop from the middle of the body, as in writing or working at a table, the muscles of the spine are not called into action; for, while the head is in this position, it rests or is supported by the ligament of the neck. The ligament, being thus kept constantly on the stretch, becomes lengthened, instead of being made more contractile, as muscles would be; and hence the stoop is increased. When this is combined with the consequences of the want of muscular action, the deeper ligaments, which bind the upper vertebræ, gradually yield; if the operation of these causes continues for a certain time, the bones and cartilages themselves become altered in shape, and consequently an almost irremediable stoop is produced[39].

This view derives confirmation, from what may be observed in the shape of the tailors in some parts of Germany, who, instead of having the erect figures of London tailors, are quite bent. On inquiring into the cause, we find that, instead of sitting as tailors do in this country, a hole is cut in the table, and a seat is placed within it; so that their position, while working, becomes nearly the same as that of persons who stoop while sitting at a table.

It may, perhaps, be objected, that labourers, and especially the vine-dressers in France, are remarkable for the complete arch which their body forms, although they bend while at work as much as the tailor does. This may also be explained; for in the labourer the bend is produced by the pelvis rolling on the head of the thigh bones, while in a person sitting as a tailor the pelvis continues nearly fixed, and the bend is in the vertebræ on the pelvis.

The erect figure of the Turk perhaps comes from the manner of sitting which is common among Eastern nations; but the heavy turban, and the spice box slung from the back of the neck, may account in a great measure for the fine figures of the Turkish Jews who frequent the streets of London. [p243]

We may even take the shoemaker as an example of the effect of a particular manner of sitting, and of frequently using the muscles of the shoulders. He is also a little in caricature, but he carries himself better than the tailor, and the cause is obvious. The tailor’s figure is very erect, but the right shoulder is generally a little higher or larger than the left, from the constant exercise given to the right arm, while the left rests upon the knee: this inequality of the shoulders is not observed in the shoemaker, because he not only uses both arms equally, but the muscles by which the scapulæ are supported, become so strong by the habit of jerking back his elbows while he works, that his shoulders always appear more braced back than those of any other class of persons: indeed, so characteristic are the figures of tailors and shoemakers, that they may be easily distinguished in a crowd.

These circumstances are mentioned, as they afford familiar examples of the principles on which we ought to proceed, in endeavouring to correct deformities; but it would be ridiculous to propose the position either of the tailor or of the shoemaker, as the best adapted to correct a stoop or falling forward of the shoulders.

The preceding observations apply also to the contrivances usually employed to keep the shoulders back, and particularly to the question of the propriety of using the common back-collar. The effect which this instrument produces in ordinary cases may be easily comprehended by the following diagram.

[p244]

The part of the back formed by the ribs is not a flat, but rather a round surface; and as the shoulder-blades rest on this, they would fall forwards were they not prevented by the collar-bones; but as these bones are united to the breast-bone by a moveable joint, and as the weight of the arms operates principally on the anterior angles of the scapulæ, both the collar-bones and the shoulders would fall forwards, were it not for the action of several strong muscles which pass from the spine to the scapulæ. But these muscles may be destroyed by any contrivance which supersedes their use. For example, let A A be the shoulder-blades, and B B the muscles which support them. If the scapulæ be brought close to the spine by the straps of the collar, and kept constantly so, there can be no use for the muscles B B. They must consequently waste and become nearly useless, while those on the fore-part of the chest, being excited to resist the straps, will become increased in power; and hence, when the collar is taken off, not only will the shoulders fall forward as in a delicate person, but the muscles on the fore-part of the chest will predominate over those by which the scapulæ should be held back, and _pull_ the shoulders forwards.

The spine and the ribs are occasionally bent so as to have some resemblance to the back of a spoon. In such cases, the shoulders not only appear high and round, but the lower angles of the scapulæ project in an extraordinary manner, because the upper and anterior angle is not only unsupported by the ribs, but is dragged forwards by the clavicles which are carried in the same direction with the sternum. When this is to a considerable extent, it constitutes the _contracted chest_ or the _chicken breast_. This, in a slight degree, is common in London, and especially among young lads; it may be discovered by the coat having the appearance of being more worn opposite the lower angle of the scapula than at any other part. Such a condition of the chest can only be completely remedied by appropriate exercises; but a collar is here necessary for a time, to keep the bones in the improved condition into which they are brought by the exercises.

These arguments will probably appear sufficiently well founded to prove that a girl, under ordinary circumstances, [p245] cannot hold her head or shoulders back, unless the muscles by which they are naturally supported are in a proper condition. Various contrivances have been proposed to strengthen these muscles. Dumb bells, if managed in a particular manner, are good; skipping, when the arms are thrown backwards and over the head, is still better; the exercises, called Spanish exercises, performed with two long poles, are also useful, but to each of these there may be objections, as they all operate more or less on the spine or ribs, which, in case of a bad stoop, are generally affected.

The following anecdote will, perhaps, set the question of the propriety of wearing the back collar in a correct point of view. A surgeon was consulted by a gentleman, who is now one of our first tragedians, as to the best mode of correcting a stoop which he had acquired. The surgeon told him that neither stays nor straps would do him any essential good; and that the only method of succeeding was to recollect to keep his shoulders braced back by a voluntary effort. But the tragedian replied, that this he could not do, as his mind was otherwise occupied. The surgeon then told him that he could give him no further assistance. Shortly after this conversation, the actor ordered his tailor to make a coat of the finest kerseymere, so as to fit him very tightly, when his shoulders were thrown back. Whenever his shoulders fell forward he was reminded by a pinch under the arms, that his coat cost him six guineas, and that it was made of very fragile materials; being thus forced, for the sake of his fine coat, to keep his shoulders back, he soon cured himself of the stoop. The surgeon was much obliged to him for the hint, and afterwards, when consulted whether young ladies should wear shoulder straps, permitted them, on condition that they were made of fine muslin, or valuable silk, for tearing which there should be a forfeit.

An inquiry into the manner a girl should sit may appear trifling to those who have not been in the habit of seeing many cases of distortion of the spine, but it is intimately connected with the present subject, and is really of considerable importance. The question has been disputed; one party insisting that girls should always sit erect, while others are advocates for a lounging position. It is not difficult to show that both are [p246] wrong;—when a delicately formed girl is supposed to be sitting erect, she is generally sitting crooked: to a superficial observer she may appear quite straight; but any one who will sit on a music stool, and endeavour to keep his body in a perpendicular line for ten minutes, will be convinced that it is difficult for even a strong man to sit as long as a delicate girl is expected to do, without allowing the spine to sink to one side or to fall forwards.

The attempt to sit erect beyond a certain time is injurious, for although bending the spine occasionally is useful rather than hurtful, yet when it is done involuntarily, and when the bend is attempted to be concealed by an endeavour to keep the head straight, there is danger of the spine becoming twisted. Indeed, a double curve is generally the consequence; there is first a bend to one side, to give ease to the fatigued muscles; and then, to conceal this, there is a second curve that is necessarily accompanied by a slight twist in the vertical line of the whole column.

The proposal to allow children to sit in a crooked or lounging position seems to have been founded on the idea that all the muscles are more relaxed in this way than even when the child lies at full length on its back. This notion is certainly incorrect, and such a mode of sitting is injurious; for even were the muscles more relaxed by it, the bones and ligaments acquire such a shape as necessarily produces distortion.

It may naturally be asked how a girl should sit, since it would appear, that whether she is in an erect or stooping posture, she is equally in danger of becoming crooked. As sitting, in the manner generally recommended, affords little or no support to one who is weak, the safest answer would be, that a delicate girl should not sit for even more than five or ten minutes without having some support to her back, and when she is fatigued, that she should lie down or recline on a couch. But as it would be very annoying to a girl not to be allowed to sit up except for so short a time, and as a couch is not always at hand, we must endeavour to show how a delicate girl may remain in an upright posture, for a reasonable time without incurring any risk of becoming crooked. This leads to an inquiry into the merits of the chairs which are at present generally used by children. [p247]

Young ladies are often obliged, while at their music lessons, to sit upon those chairs, which have high backs, long legs, and small seats. These chairs are said to have been invented by a very eminent surgeon, and are intended, either to prevent distortion, by some supposed operation on the spine, or as the most effectual means of supporting the body. It is difficult to imagine how a chair of this description can effect the first purpose; and to discover how far it is calculated for the second, the reader should make the experiment on a chair of the same proportion to his figure, as the chair in question is to that of a little girl. He will find that if the seat or surface on which he rests is small in proportion to his body, the chest will, after a time, either fall forward or to one side, unless he exert himself to a degree that is very fatiguing. Indeed, if the seat be at the same time so high, that the feet do not rest fairly on the ground, but dangle under the chair, a forward position of the head is almost necessary to preserve the balance of the figure[40].

The objections to such chairs have been met with the assertion, that girls feel remarkably comfortable in them. This is no argument in favour of their use, for it is not uncommon for a girl who has seven or eight pounds of iron strapped upon her body and next to her skin, to say the machine annoys her so little, that she does not care how long she wears it.

But whether this chair is agreeable or not, it is easy to show that it is not calculated to give much proper support to the body, and that it is almost impossible for a delicate girl to sit long in a natural or easy position upon it.

It may be allowed, that the chair which we consider the most comfortable, that is, the chair which affords the most support to the body, should, if made in proper proportions, be the best for a delicate girl. In such a chair, the _seat_ should be scarcely higher than the knees (thus permitting the whole of the foot to rest on the floor), and of such a size, that on sitting back, the upper part of the calves nearly touch it. This form of _seat_ is very different from that of the chair alluded to, the _back_ of which is also equally objectionable, for, instead of being in [p248] some degree shaped to the natural curves of the spine, it is made nearly straight, and projects so as to push the head forwards. A delicate girl should always sit so as to rest against the back of the chair, and, if the lower part of her spine is weak, a small cushion will afford great relief. As it is quite a mistake to suppose that the shoulders, if raised in any other way than by the action of the muscles, or by the curvature of the spine and ribs, will continue high, there is no real objection to a girl who is delicate being supported by an arm-chair; for, by occasionally resting on the elbows, a considerable weight is taken off from that part of the spine which is the most likely to yield.

These observations refer only to the manner in which delicate girls, whose spines are still straight, should sit: when the spine is actually distorted, it will be necessary to use other means.

FOOTNOTES:

[37] For this, and some other communications upon the same subject, we are chiefly indebted to our much-lamented friend and correspondent, the late Mr. Shaw, Surgeon to the Middlesex Hospital.

[38] When the Russians wish to give a horse high action in trotting, they accustom him, while young, to wear heavy shoes on the fore feet. The resistance to be overcome necessarily increases the strength of certain muscles; and hence, when shoes of the common size are put on, the horse lifts his feet higher than one which has not been subjected to this discipline. Some opera dancers practise with lead weights on.

[39] Elderly persons may recollect how often the girls who worked at _tambouring_ were crooked: the present fashionable amusement of embroidering seems to have, in some instances, the same effect.

[40] It must be almost unnecessary to remind the reader, that if the knees are bent in standing or walking, there is a curve in the spine at the same time.

_A Critique on the Aplanatic Object-Glasses, for diverging Rays, of_ Vincent Chevalier, ainé et fils. _By_ C. R. Goring, M.D.

The curiosity of many will doubtless be excited, as to what our neighbours, the French, ever foremost in the pursuit of glory, both in arts and arms, have been doing in the affair of achromatic object-glasses for microscopes. With the highest satisfaction I find myself enabled to state, that Messieurs Chevalier, (ainé et fils,) No. 69, Quai de l’Horloge, Paris, have rivalled our own artists, in this branch of the manufacture of optical instruments.

Mr. J. Lister, actuated by a most laudable zeal for the prosecution and advancement of optical science, as it concerns microscopes, caused me to order for him one of Messrs. Chevalier’s instruments, _in Mr. W. Tulley’s name_; for, as Mr. L. wished that Messrs. C.’s pretensions should be fairly and thoroughly scrutinized, it was but fair that the latter gentlemen should be stimulated to do their utmost, by a consideration of the science of their customer. A critical examination of the object-glasses of this instrument (for making which every facility was afforded me by Mr. L.), forms the subject of the present paper. [p249]

I here, then, enter upon the discussion of the merits and demerits of the objectives of the said instrument[41], these being much more perfected than those of another, of previous make, which I saw in the possession of Mr. Howship, of Great George-street, Hanover-square, to whom I received a letter of recommendation from Mr. Spilsbury, of Ball-Haye. To the signal politeness of these gentlemen, in furthering my views, I am greatly indebted.

Four object-glasses accompany Messrs. Chevaliers’ instruments (at least those marked _perfectionnés_,) usually rated at the following foci: 14 French lines, 10 ditto, 4 and 4: the two latter combine together at will, and give a focus of two lines.

14.) Focus about 1.42 of an English inch, clear aperture 0.31, original aperture as reduced by a stop, 0.10.

It is perfectly achromatic with its clear aperture, and may be used without a stop on most transparent objects; requires to be cut off to 0.23, to give the necessary distinctness for opaque ones.—(When I speak of the apertures which C.’s lenses will bear, I must be understood, here and elsewhere, only with regard to the _middle of the field of view_, or rather that part of it where the distinctness is greatest[42], for double object-glasses give the central rays only correct, and confuse the oblique ones very much, for which reason, conjoined with the small apertures they admit of, they were abandoned by Mr. Tulley, for the triple construction, the true and regular form for the microscope.)—There is an excess of spherical aberration in convex lenses; neither are the glasses well ground, or centered, or duly adjusted. The concave of this object-glass is tarnished, and there are traces of seediness in the cement, which is, indeed, to be seen more or less in the whole of them.

10.) Focus about 0.91, clear aperture 0.23, original stop 0.09. [p250]

This object-glass is under corrected in point of colour, and wants to be made longer in the focus to be achromatic. The excess of uncorrected spherical aberration is in the convex lens; the glasses are not well ground, centered, or adjusted; the same appearance of tarnish as in 14; bears its clear aperture for the middle of the field on most transparent objects, but must be cut off to 0.2 for opaque ones.

Both of these object-glasses are ineffective upon test objects, from want of sufficient power and aperture.

4.) Focus about 0.43, clear aperture 0.23, original stop 0.09, perfectly achromatic. The uncorrected spherical aberration is in the concave; centering and grinding very fine, but in very bad adjustment; shows some transparent test-objects pretty well with its clear aperture, and, cut off to about 0.16, performs well on many opaque ones.

2.) Focus about 4.7, clear aperture 0.21, no stop, perfectly achromatic, surplus of spherical aberration in the concave as before; centering and grinding very fine; adjustment tolerable; in other respects very similar to 4. This object-glass being adjusted, does more singly on test-objects than any other, and carries an aperture of 0.16 well on opaque bodies, showing the lines on the diamond-beetle’s scales strong and well cut out.

Combination of 4 and 2—(quadruple.)

I am happy to be able to speak in terms of almost unqualified approbation of this composition. It, of course, surpasses the performance of any single triple-glass, _on those test-objects which require extravagant angles of aperture_. The field also is good all over; or at least would be, if the glasses were in adjustment, which is the only drawback upon it. The focus of the combination is only 0.26, yet it performs admirably on transparent test-objects with its naked aperture of 0.23, and is very fine on opaque ones with 0.16, and doubtless would carry 0.2, if the adjustment was duly carried into effect.

Messrs. C. have, I think, most assuredly here hit upon one of the very best _compositions_ for the object-glass of a microscope; all the imperfections of double object-glasses, _taken singly_, are here done away, while their thinness and agglutination into one mass allows of their combining together almost as if they were simple plano-convex lenses, leaving moreover abundance of space for the illumination of opaque bodies. [p251]

I must here state, that Messrs. C.’s object-glasses are all stuck together, I believe, with fused gum-mastic, or, perhaps, with very thick mastic varnish. This practice seems, in theory, to be bad, most especially if the curves united together are not of the same radius; nevertheless, practically speaking, the process of soldering seems to me to do more good, by the obliteration of two surfaces, and by keeping the glasses immovably adjusted, than harm in any other way. I cannot, in fact, discover any very sensible difference in the optical performance of these small achromatics, whether stuck together or not. I _fancy_ that they have a little more light and clearness when cemented, (as they certainly should have,) but cannot be very positive. I hold it as a maxim in practical optics, as in our common law, “de rebus non _apparentibus_ et non existentibus eadem est ratio.”

I may observe, that Mr. Lister has combined that marked 10, with 4, and finds the performance proportional to that of 4 and 2.

It will be remarked that Messrs. C., from an apparent ignorance of the value of aperture; and perhaps impressed with the too common and prevalent idea, that, having once obtained distinctness and achromatism in their object-glasses, every thing else might be accomplished by a condensation of artificial light, have reduced their apertures to such a degree, as to render their instrument as ineffective upon test-objects as a common compound; for when the opening of an aplanatic glass is cut off to the same diameter as a common one, it shows _nothing more_, though it will certainly exhibit objects far _more satisfactorily_. Upon the apertures of microscopic lenses their effects entirely depend, as was remarked a long time ago by the great Huygens. An achromatic glass is more valuable than another, merely on account of the larger aperture it will bear, without causing aberration, and consequent indistinctness. Those who are in possession of Messrs. C.’s microscopes should get the stop behind the object-glasses turned out, and procure others to be used ad libitum, according to what the goodness of the object-glasses will permit.

I feel myself called upon, however, to state, that, since the completion of Mr. L.’s microscope, Messrs. C. _have enlarged the_ [p252] _apertures of their object-glasses to the requisite angle_, and have moreover _arrived at the true method of adjusting them_, so that they are _now_ free from those objections which applied to Mr. Lister’s, and are in all respects unexceptionably finished.

I know not if any dispute will ever arise hereafter, as to who is to be considered as _the original maker of effective aplanatic object-glasses for microscopes_[43]. It is of very little consequence in the present instance, for it so happens that Mr. Tulley and Messrs. Chevalier have been so totally unconnected with each other, and have worked upon such totally different principles, that it must be evident, on the most superficial consideration, that both are entitled to the honour; nevertheless I apprehend it can be proved that Mr. Tulley made an effective one before the Chevaliers, having completed his in March 1824. The date affixed by Chevalier to his first instrument is 1825[44].

It requires moreover a stretch of complaisance, not to be expected on this side the Channel, to be enabled to admit that the best double object-glass is (_taken singly_) effective; or that, in consequence, Chevalier made an _effective one until he had enlarged his apertures, and combined two together_[45], which combination is not to be met with in his primitive instruments. Mr. Lister, (to whom the public is mainly indebted for the present eclaircissement concerning Chevalier’s instrument,) has, by a peculiar method of his own discovery, measured the [p253] curves, thicknesses, and diameter, &c. of that marked 14, which I here give (unfortunately one of the least effective of the set,) however, in all probability, the rest are constructed on the same principle; the annexed drawing by Mr. L. will sufficiently explain itself. Nothing can surpass the beautiful simplicity of Chevalier’s, or rather Euler’s, curves, which, it will be observed, are all alike[46]. The production of _deep_ achromatics must ever be a task of some difficulty, even to those who thoroughly understand their humours and punctilios; and unscientific artists will, I think, be much more likely to succeed on the French plan, than the English one. Two double object-glasses, by themselves, are very poor things; but, when combined, perform admirably, and will, I believe, (if the three curves are of equal radii,) be far more easily executed than one of the triple Tulleian construction. The dense flint-glass of Guenard, or Frauenhofer, however, will be an indispensable requisite, from the nature of the curvatures. A triple Tulleian object-glass, and a thin double one of Chevalier, (a composition first conceived and adopted by Mr. Lister,) form an excellent combination, and give a very vivid light, without softness, dulness, or nebulosity. This, I think, is the extreme number of glasses which ought to be tolerated. Let it never be forgotten, that _a really good triple glass will bear an aperture quite sufficient for ninety-nine objects out of a hundred_. I myself denounce the practice of combining glasses together, _in all those cases where they are capable of doing their work alone_. I shall always consider it as a clumsy, bungling, and unworkmanlike method of obtaining a short focus, combined [p254] with a large angle of aperture. If a man aims at perfection, and wishes to distinguish himself in this branch of optics, let it be done by working perfect triple glasses of 0.2 and 0.3 inch focus, with 0.1 and 0.15 of perfect aperture, like those of Mr. W. Tulley and Mr. Dollond, or deeper still, if he is able; and it is with the most cordial satisfaction that I am enabled to inform my readers, that Messrs. Chevalier (duly appreciating the regular triple construction as the true form for the microscope) have applied themselves diligently to the manufacture of this species of objective, from which they have already had excellent results. It is a fundamental principle, that all superfluous refractions and reflections are to be avoided in the construction of optical instruments. As a radical reformer of microscopes, I can tolerate no abuses in them, or show any quarter to their abettors. Messrs. Chevalier have also undertaken the manufacture of achromatic and catadioptric microscopes, after the fashion of those made by Professor Amici, of Modena, which were so much and so justly admired by the cognoscenti of this country.

It only remains for me to observe, that though two double-cemented object-glasses form the most perfect _combination_ from the fewness of their surfaces, and consequent brightness of their image, yet a fusion between the Tulleian and Eulerian constructions seems to be the _most convenient_ for general use; by this, of course, I mean a triple glass with a double one, to apply before it occasionally, à la Lister. Mr. Dollond and Messrs. C. have demonstrated that two object-glasses _may be combined with the best effect, which are both good, and work well separately_; but Mr. Tulley has constructed a double one, which, useless by itself, when applied over a triple one, (made to act singly,) corrects that excess of spherical aberration in the concave lens, (by its own excess in the convex,) which, when the aperture is large, is the eternal vice of all the best single and compound object-glasses for diverging rays which I ever saw. This is perhaps the ultimatum of improvement, though a quadruple one, on the same plan, might have the advantage in greater light and clearness, from its simplicity, and the paucity of its surfaces.

The quadruple or quintuple object-glasses are those which [p255] are best adapted for the solar microscope, for they give a full-sized field of view to this instrument, good to the edges, which no single object-glass will do, as I have had occasion to remark in my paper on Mr. Tulley’s aplanatics, unless converted into a compound, by means of eye-glasses, &c. This popular and highly amusing instrument will now receive the utmost reformation and improvement of which it is capable, and become truly scientific in its construction: hitherto it has been a mere toy, but one degree removed from a magic lantern.

I shall now allow Messrs. C. to say what they can for themselves, and to detail the various modifications which they have introduced into their instruments, since they executed Mr. Lister’s order, by giving a translation of a letter I have received from them on the subject, and shall conclude by expressing a hope that no national or illiberal feeling has entered into the composition of this critique, and that I have used my oil, vinegar, and pepper in correct proportions.

“_Paris, Oct. 15_.

“Sir,

“Accept our thanks for your extreme complaisance in offering to publish the results obtained by us in the construction of microscopes. Since the order executed for Mr. Lister, we have improved those instruments last completed, by greatly enlarging the diameter of the illuminating mirror, in order to obtain still greater light. The prism for opaque bodies is diminished about one half, and by a small modification in its mounting is rendered more serviceable: the diminution of the length of the body has enabled us to augment the magnifying powers by different eye-glasses, and the four double object-glasses placed in a better mounting can be used separately or in superposition, according to the pleasure of the observer, either to form quadruple objectives, or even to combine in a mass together. This last arrangement produces a great accession of magnifying power, without injuring the clearness of the image or arresting much light.

“You see, Sir, that we have the pleasure of coinciding perfectly in your opinions about improvements, for we adopt the quadruple object-glass as the best, and we give three changes [p256] of eye-pieces. The double motion given to the body of a microscope is, in our idea, the defect of all those hitherto constructed; for, as the optical part should remain perfectly centred with the mirror and the diaphragms, it is evident that the least derangement of it from this position must destroy the perfection of the image: the stage then only should move[47] without affecting the diaphragms or the mirror, and in this we [p257] have well succeeded in the construction of the microscope of Sig. Amici. But all these arrangements much augment the price, and an observer ever so little practised will always find the object easily enough by means of his hands.

“The prices of our achromatic microscopes are as follows:—

“_Achromatic microscope_, like Mr. Lister’s—300 francs.

“The same, with the latest improvements, three eye-pieces, and camera lucida for drawing the magnified objects—400 francs.

“_Amician Microscope_, one horizontal achromatic, the stage giving all the motions to the object, with a micrometer screw, five eye-pieces, two camera lucidas, hand magnifier, frog trough, accessary apparatus, &c. _One catadioptric microscope_, mounted on the same stand, and adapting itself to the same apparatus; the two instruments inclosed in a mahogany case—1000 francs.

“We trust that the very moderate prices of these instruments, together with the care which we bestow on their construction, will procure us orders for them. Their superiority has been duly recognized by the jury of the Exhibition of the Products of Industry, which has been pleased to decree to us a silver medal.

“The Amician achromatic microscope is composed of a tube seven inches long, at the extremity of which is placed a prism, which reflects at a right angle the rays which come from the object-glass, composed (_as in our microscopes executed since 1824_) of four double object-glasses, which may be used separately, or two, three, or four at a time. The stand is a square bar, which has a rackwork, carrying a moveable stage, which, by means of adjusting screws ingeniously disposed, permits an object to traverse the field of view in every direction. This disposition gives the power of determining the real dimensions of objects submitted to observation by means of the micrometer screw, which is placed at the side, while the camera lucida affords the means of drawing their outline, and consequently of measuring the magnifying power.

“The rays proceeding from the object which have passed the object-glass, and have been rendered horizontal by the prism, are received by different eye-pieces disposed after the manner of [p258] Ramsden. Their power can be varied. Each instrument carries six, five of which can be attached at pleasure either to the catadioptric or the achromatic. The deepest belonging to the reflector is a single lens of half a French line focus, and the most powerful of the achromatic is a line and a half.

“Such, we think, are the details which you required: we wish that they may prove agreeable to you.

“We beg you to accept the assurance of the high consideration with which we are, Sir,

“Your very devoted Servants,

“VINCENT CHEVALIER, ainé et fils.”

“69, _Quai de l’Horloge_.”

FOOTNOTES:

[41] The objects employed by me in looking into the defects and excellencies of these glasses, were an artificial star, and a piece of enamelled dial-plate, the phenomena presented by which, _when put out of focus_, incontestably warrant the judgment I have pronounced upon them, as any, true optician will admit.

[42] When an object-glass is out of adjustment, its maximum of distinctness is not in the centre of the field of view, but somewhere else, according to circumstances.

[43] The question must naturally resolve itself into this point, for achromatics for microscopes, (as they are called,) were made by Dollond, Martin, and Pollard, many years ago; the only objection to them was, that they were _not effective_, consequently, _nominal only_, and useless. I defy any man to produce an _effective_ object-glass, which can satisfactorily be proved to have been made before 1824.

[44] See the _first_ instruction published by Messrs. C. along with their microscopes: “Microscope Achromatique selon Euler,” &c. I apprehend there is a misdate in Messrs. C.’s letter at the end of this paper, where they state they have made the achromatics _since_ 1824, _with four objectives_, which implies that they also made them before that period, but in another way.

[45] Mr. C. Tulley recommended the combination of two achromatics together from nearly the beginning of his son W.’s labours upon them, who rejected the idea, together with myself, as giving rise to too great a complication, _always supposing that triple glasses must be used_. I myself combined two triple achromatics together, for experiment sake, in a very early stage of our proceedings, but liked not the result, though effects were certainly produced by the composition, which could not be obtained from the best individual triple one.

[46] The theory on which these object-glasses are constructed is contained in a paper of Euler’s, published at St. Petersburgh, in 1774. Messrs. Chevalier have caused it to be inserted entire in the “Bulletin de la Société d’Encouragement de Paris,” No. CCLIV., for Aug. 1825.

[47]

This is the theoretical view of the case, the practical one is different, as frequently happens. _Opaque objects_ are not affected at all by the eccentricity of the axis of the body: nor can I recollect that I ever felt any particular inconvenience from the motion of the optical part, even with transparent subjects, unless it was thrown _very much indeed_ out of the axis of the illuminating mirror. On the other hand, it is notorious that _living_ aquatic insects and animalcules are the most _popular_ and _entertaining_ objects which microscopes can show. These are, for the most part, abundantly restless; and if the stage on which they are placed has any motion, their natural unquietness is so much exasperated, that it becomes almost impossible to get a good observation of them at all. I once set to work at making some drawings of a variety of new and original objects of this class (which, I trust, will one day be published) with a microscope having all the requisite motions applied to its stage, and am confident that I had thrice the labour fairly appropriate to the execution of my task from this oversight. The very tremor produced by the transition of a carriage in the street, is frequently sufficient to unsettle live objects when disposed to be still and quiet, and put them in a fidget for a quarter of an hour. It is very unfortunate that the mountings of optical instruments are made in general by mere mechanics, who seldom or never observe with them, and consequently know not the exigencies which occur in practice. It is still more unfortunate, that in the science of fitting up microscopes, an ounce of a man’s own wit is worth about a ton of his neighbour’s. Was it not that I dislike to verify this adage myself, I should recommend the following motion to be applied _to the body_:—let the socket of the arm which carries it have a smooth rotatory motion on the head of the bar in the usual way, conjoined with another horizontal one produced by rackwork attached to the said socket. Let the pinion which belongs to the latter movement be made very strong, so that a lever about three inches long may project from its centre: this is to be held in the hand, the thumb and index finger operating on the rackwork, while the two little fingers give a rotatory motion by working the lever end. _This rapid double motion is here completely under the command of_ one hand, _while the other is at liberty to adjust the focus_. I know of nothing better for general purposes, or in particular for following the motions of live insects, &c.; but when _only inanimate ones_ are to be the subject of microscopical study, I prefer the motion of the stage, for the reasons stated by Mons. C.

_On the Existence of Chlorine in the Native Black Oxide of Manganese._ By John M’Mullen, Esq.

In the paper relating to this subject, which the editors of the Quarterly Journal of Science obligingly inserted in the forty-fourth number of that work, I described some experiments which I had made, to show that chlorine is uniformly evolved from the Native Black Oxide of Manganese by the action of sulphuric acid, under certain circumstances, which I endeavoured to detail with strict accuracy, so as to prevent any mistake or failure in the event of the experiment being repeated.

Upon this paper Mr. Richard Phillips has made some observations in the Philosophical Magazine and Annals of Philosophy for April last, to which I am desirous of briefly adverting. He says, “Mr. M’Mullen having observed, when sulphuric acid is added to peroxide of manganese, that chlorine is evolved, he conceived it might be derived from an admixture of muriate of manganese, iron, or copper; but having washed some of the peroxide of manganese with water, he did not find that any chloride of silver was precipitable from it; he, therefore, concluded that the peroxide in question contained no muriatic salt.” If Mr. Phillips will take the trouble to refer to my paper, he will find that this is by no means the statement which it contains. I observed that, in order to separate any soluble [p259] muriates which the oxide used might, in the first instance, have contained, “I washed it every day, for three weeks successively, using sometimes hot and sometimes cold water: _at the end of that time_, I tested the water, which was _then_ decanted from the washed manganese, by the nitrate of silver, but without finding the slightest appearance of precipitated chloride. I then poured upon the manganese four times its weight of dilute sulphuric acid; allowed the mixture to stand _for about four weeks_, occasionally agitating it, and at the end of that time, found, when the dilute acid, now of a deep crimson colour, _was removed from the subsident manganese_, and the latter agitated, that the most decisive evidence of the presence of chlorine was exhibited in the vapour evolved from it.” I stated further, that I had “carefully preserved this particular mixture, and that after a lapse of more than twelve months, the residuary manganese, when the supernatant acid was removed, continued to evolve chlorine.”

In this experiment my object was effectually to purify the manganese used from any soluble muriate which might by possibility have been mixed with it: I did not, however, test the water _first_ used in washing it, but merely that which was _last_ removed from it.

Mr. Phillips proceeds to observe that he had prepared some observations, and at considerable length, _to prove_ that the author of the above paper has been completely misled by “forced analogies” and “erroneous experiments;” but that it _afterwards_ occurred to him, that it would be better to show, in a few words, the real source of the chlorine in question, the evolution of which from peroxide of manganese _he had noticed some time previous to the publication of my papers_. That with this view he had procured various specimens of the peroxide of manganese, (one of them in the crystallized state,) which were reduced to powder, and on the addition of sulphuric acid, chlorine was evolved from each. That he then washed separate portions of them with distilled water, and on the addition of nitrate of silver to the washings, chloride of silver was immediately precipitated: sulphuric acid being poured upon the washed peroxide, no chlorine whatever was evolved. That he further added sulphuric acid to an unwashed portion, and to one which had [p260] been washed, and referred both to a _bystander_, who immediately detected the odour of chlorine in the former, but not in the latter. He then proceeds to show that the specimens of manganese which he had made the subject of this experiment contained a portion of lime, and he infers that the black oxide of manganese consequently contains muriate of lime.

Mr. Phillips asserts that I have been misled by erroneous experiments. My reply is, that the experiment to which he refers, and which I have recapitulated, was carefully made, and is truly and faithfully detailed. In what, then, is it erroneous? It is not incompatible with that which he has produced as a refutation of it, inasmuch as he did not wait the result for which the perusal of my statement should have prepared him, and which he clearly should not have anticipated. He states that chlorine was not evolved from washed manganese at the instant when sulphuric acid was affused upon it. This is not a contradiction of my statement: I affirmed that, after washed manganese had been exposed to the action of sulphuric acid for a very considerable period, I distinctly observed the evolution of chlorine, and that for twelve months afterwards, _under the circumstances detailed_, this continued to be the case:—all this I deliberately re-assert. I have frequently met with specimens of manganese which, upon the first affusion of sulphuric acid, gave off chlorine; but _in general_, as far as my experience goes, _this is not the case_: were it of uniform occurrence, and that the mixture of sulphuric acid and oxide of manganese rendered chlorine evident to the smell, the fact _could not have remained unnoticed till now_.

The observations of Mr. Phillips, to which I now refer, did not come into my hands till about three weeks ago. It fortunately happened that I had still preserved the specimen of washed manganese upon which sulphuric acid had been affused, under the circumstances already recapitulated, and it occurred to me that this would afford occasion, as decisive as I could desire, to put the accuracy of my original experiment, and the conclusions drawn from it, to further proof. I am bound to premise that this specimen of manganese, after having been in the first washed and subjected to the action of sulphuric acid, as already mentioned, has ever since remained in [p261] the vessel in which the experiment was at first made, covered with dilute sulphuric acid,—a period of more than eighteen months; and it will scarcely be doubted that, in the course of that long interval, any muriate of lime which it might have originally contained must have been thoroughly decomposed. Upon removing the supernatant acid, the residuary manganese gave sensible evidence of the presence of chlorine; paper stained with the solution of indigo in sulphuric acid was readily bleached by it, &c. I now proceeded to wash the manganese in pure water, and continued to do so until the acid was no longer perceptible to the taste. I then washed it three times successively with distilled water, and after decanting off the fluid of the last washing as closely as possible, added pure sulphuric acid in considerable quantity, and stirred the mixture thoroughly, after it had cooled, with a glass rod. At this time no vapour of chlorine was evident either to the smell or to the usual tests. The mixture was then set aside, and allowed to stand undisturbed for ten days: at the end of that time, when the acid was poured off, and the subsident manganese agitated, the vapour of chlorine was as distinctly manifest as when it was first subjected to experiment more than a year and a half ago.

_Dublin, June_ 11, 1827.

_Modern Improvements of Horticulture_.

That gardening has always been one of the most natural, as well as the most useful occupations of mankind, is obvious: that it has advanced—been retarded—or flourished, according as general taste or wants, or peculiar political, moral, or local circumstances, were favourable or adverse, is also sufficiently evident from all historical testimony;—but in no age has it advanced with such rapid strides towards perfection as it has done within the last fifty years. To bring the modern improvements in array before the reader,—to estimate their advantages in a public and private point of view,—to look forward from our present elevated station to the probable results of continued, and extended application,—may be an amusing, if not an [p262] useful inquiry: it may tend to remove barriers which are only imaginary, and by freeing the thinking powers of practitioners from the trammels of custom, lead them forward into that expanse of operative freedom, where much remains for the exercise of the inquiring mind, and experimental hand, in exploring the yet untrodden field of practicability, and calling forth the still latent powers and susceptibilities of pregnant nature.