Some time since I had a model of a rotary engine in the Adelaide Gallery, with the drawing; the slides in this were placed within a centre wheel, similar to one patented by Messrs. Bramah and Richardson; excepting this, that the former had a fixed guide, or tappet, acting upon the projecting arms of the revolving slides, instead of pressing continually upon the inner circumference of the cylinder chamber; this, and the foregoing plan, I abandoned, for the following reasons:

1. Because of the great friction produced by the circumference of the inner wheel.

2. Because that the slides, not having any support within the chamber of the cylinder, were liable to strain.

3. Because the stress of power rested upon the opening through which the slides passed.

4. Because the slides required to be packed, which increased the friction.

5. Because (in the last of the above plans) the pin, or roller, struck the guide with such abruptness, that it might prove destructive to the machinery when in rapid motion, besides producing an unpleasant concussion and noise.

I perceive, from your monthly Part 137, No. 784, that a patent has been obtained by a Mr. Rowley, of Manchester, for a rotary engine, so similar to the foregoing, that I cannot refrain from noticing it, especially as the guides, or racers," and the method of using the pins" or rollers to run within them, are so particularly named. I would beg your correspondent, Mr. Evans, to refer to No. 728, p. 244, and he will there find that these parts are specified as original.

Now, as I have a slight variation in my own plan, not sent you, which, if put into practice, might be considered an improvement, and which, without the use of the guides or "racers" I cannot apply, I would ask-am I to be debarred from using them, because of a subsequent patent? * The plan and arrangement were given to the public; and I consider I have still the privilege of the invention, equal to others.

*The distinctive features of most rotary engines are so faintly marked, that it is hazardous to answer this question without an attentive examination of the two plans. Whether Mr. W. can use the "rollers" and "racers" referred to, altogether depends on the method in which he has applied them to effect his object.-ED. M. M.

The contending opinions, as to the effectiveness or non-effectiveness of the rotary engines, will, I trust, very soon be at an end, and practical results take precedence of theoretical suggestions, placing their merits beyond the influence of conjecture or surmise. The difficulty of rendering the different joints steamtight has been stated to be a principal objection, as it might very well have been 20 years since; but, I would ask, where are all the improvements in mechanical science, the correct adjustment of metallic packing, or the boasted advance and perfection of machine making, if such is to continue the exclusive plea for relinquishing the use of engines, the advantage of which is, on many accounts, admitted?

There was a time, in the infancy of science, when the power of steam was applied without the aid of the reciprocating engine; and no one can now assert, that the reciprocating engines will alone keep the field;—an engine having few parts, and the arrangement of them such as can be easily adjusted to keep it steam-tight, being the only requirements to bring into competition a rotary engine to maintain the rivalship. For, where the saving of room or the increasing of velocity is an object, there is little chance but that the former will give place to the latter; as the power of steam may be applied at so small a cost, and used in so many ways, where it could not be conveniently arranged upon the reciprocity principle.

I have felt more assured, that the opinions that the wear and tear to which the rotary engines are said would be subject, and that the evils arising from this, would prove more than equal to any benefit that could possibly arise under every consideration-are erroneous, from this circumstance being continually brought to my recollection by the asserted experience of those who have engines in use that have metallic packing,―viz., that the more they are worn, the truer and better they work, that this should be a plea, therefore, in favour of one and against another movement, is a paradox which can only have originated in assertions made without consideration, and cannot hold good for the one more than the other.

In the plan of the model in the Gallery, the rotary principle produces the re

=

found by producing the chord CE in the same manner as was before done with the chord A C, and drawing new perpendiculars each to 2 B C. Now it may easily be proved, that not only the data by which the value of B C is assumed are incorrect, but that the curve thus determined is very far from being circular, on the contrary, one in which the radius of curvature is continually increasing.

Produce B C to K, and draw FE parallel to B K, join C H, A E and C ́E. Ist, It is evident that A B2 is not diam. (A H)

equal to B C or A D, for (Cor. 8th Euc. 6th).

AH: AC::AC:AD

=

=

2ndly, Where G E is assumed to be= to 2 B C is decidedly wrong. For (Euc. 32nd 3rd b.) << BAC = <AE C; but in AGCE the < GCE two interior and opposite angles CA E and CEA (Euc. 32nd, 1st b.).. 4 GCE= <BAE. Now the two As BA K, GCE are similar and equal; wherefore, (Euc. 26th, 1st b.) G E B K. Again, since in A AFE, C K is parallel to F E AF: AC ::FE: CK (Euc. 2nd, b. 6th); but A Fis less than 2 AC.. FE is less than 2 CK -much more than is G E or its = B Kless than 2 CK (since FE is the hyh. of the right angled ▲ GFE). And as BK is divided into two parts B C, C K, if the whole B Kbe much less than twice one portion C K, it evidently must be much greater than twice the other B C .. B Kor G E is much more than 2 B C ; therefore, admitting the locus of the point C to be on the circumference of a circle of the given radius, the point E is not, if GE is made to 2 B C—Q. E. D.

=

"This is the patent age of new inventions For killing bodies, and for saving souls, All propagated with the best intentions." BYRON.

Sir,-In our uncertain climate, artificial warmth is an indispensable comfort of life, and various methods are continually resorted to for obtaining it. The extravagant cost of fuel in most parts of our island, renders due economy of heat, and its several sources, a subject of paramount importance. In seeking with too much eagerness after this object, it too often, unfortunately, happens that another circumstance, equally essential to our health and comfort, is altogether lost sight of,-viz., pure and wholesome air.

Our forefathers, of the last two centuries at least, were feelingly alive to the importance of perfect ventilation, both in their streets and houses; but there exists a very strong disposition at the present time to disregard their wise admonitions on this head, confirmed as they are by all subsequent experience, and human life must be sacrificed "to save two-pennyworth of fuel per diem."

The opinion of Dr. Ure upon the modern innovations in "domestic warming stoves," inserted at page 127 of your 798th Number, is deserving of the utmost attention; the pernicious, and slowly fatal effects of " mephitic stoves" (of all kinds) is ably pointed out, and a sufficient caution given against the evil consequences of over-heated and unventilated apartments.

The late lamentable catastrophe in St. Michael's church seems likely to direct a proper degree of attention to the subject of ventilation, and to the avoiding of stoves and fuel, liable to be productive of so much mischief. Under all the circumstances of the case, I apprehend the verdict of the coroner's inquest on the body of James Trickey-("poor fellow! his was an untoward fate,")-must be considered satisfactory and just; though, certainly, not quite in accordance with the weight of evidence brought forward by Messrs. Harper and Co. The jury happened to be sufficiently well-informed to see through the misrepresentations made to them, and mainly supported by

what you have very properly designated as "one-sided experiments." There can be little doubt in the mind of any reflecting person, that if poor Trickey had remained in an erect position, either sitting or standing, he would have suffered little or no inconvenience, from the noxious effluvia of the burning charcoal. But there is every reason to believe, in fact, the medical evidence proves as much, that he was seized with an attack of apoplexy-to which, from his full habit of body, he might have been considered exceedingly liable and fell prostrate upon the pavement of the church, when he instantly became immersed in a strátum of carbonic acid gas, which quickly completed the work of death.

In consideration of the evidence given by Dr. Golding Bird and Mr. Blenkharne, I have been informed that one of the gentlemen who was present at the inquest, has since performed several experiments with Harper and Joyce's pa tent prepared charcoal in one of their stoves, and he has found, that although he was in no way inconvenienced by the effluvia proceeding from it while burning, yet, on placing some small birds on the floor of the apartment they were very soon suffocated. A favourite dog had also very nearly fallen a victim to the experiment, and it was a considerable time after being taken out of the room that he recovered his usual faculties; fully proving the existence of carbonic acid gas, in considerable quantity, upon the floor of the apartment.

It is most disgraceful to the age in which we live, and derogatory to the character of real science, that men should be found, eminent for the supposed extent of their learning, and yet base enough to sacrifice "the truth of science" at the shrine of friendship or of interest. It appears to me, that persons of this class too often imagine that their office, like that of members of the legal profession, is to take up and stoutly maintain whichever side of the question they are hired to defend; to supply opinions "to order," with experiments "to match," and so to mistify and quibble, or to conceal or misrepresent facts, as to make, if needs be, "the worse appear the better cause.

In criminal matters, the greater the rogue and the more palpable his villainy, so much the greater credit is given to the pleader who shall get him off scot free." So in the world of science it

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would seem to be imagined, that the clearer the fact and the more incontrovertible the evidence-so much the greater praise is due to him who shall most effectually bamboozle his hearers and persuade them that black is white in spite of the evidence of their senses. I have understood that a very strong feeling of disgust prevailed with respect to the evidence of some men of high standing in science" upon the melancholy inquiry before alluded to, and it has been stated, that had the jury been sitting elsewhere, and not composed of friends and neighbours of Mr. Harper, certain learned professors would have been put to open shame; but it was felt, that in dealing with them according to their deserts, Mr. Harper's cause would be seriously injured, and therefore they were permitted to detail experiments and make statements, at which the veriest tyro in chemistry knew to be fallacious and un

true.

The idea of a heavy fluid like carbonic acid gas, which requires to be heated about 250 degrees of Fahrenheit above the atmospheric air to acquire the same specific gravity, being found at the top of a capacious building, the air of which, originally at 50°, was only raised 10° in twelve hours by the combustion of 49 pounds of charcoal, is absurd beyond credence.

The tale about the heat descending into the vaults beneath the church and extracting deleterious vapours from the coffins, must have been got up by some wag as an excellent satire upon the statements of the learned professors. With quite as much truth, and with more apparent reason, might it have been asserted that the carbonic acid gas had descended into the vaults and suffocated the corpses in their coffins!

I remain, Sir, yours, respectfully,
WM. BADDELEY.

London, Dec. 6, 1838.

MR. PRITCHARD'S MICROSCOPIC

ILLUSTRATIONS."*

The microscope is of about the same antiquity as the telescope; but until within the last twelve years it remained an instrument of comparatively small

* New edition, emended and enlarged. 1838. 248 pp. 8vo., with numerous plates. Whittaker and Co.

utility. The achromatic principle which was at once adapted to the telescope with astonishing success, was productive of no such happy results on its first applicetion to the microscope. Swammerdam, Lewenhoek, De Torre, Euler, and others, applied themselves with great industry to the discovery of some means of remedying the defects of spherical and chromatic aberration to which the simple microscope is subject, but missed the way to the object of which they were in search, by assuming it for granted that the smaller the angle of aperture the better. To such an extent was this notion pushed, that Lewenhoek had lenses with a focal length of not more than 1-700th or 1-800th part of an inch. To the acute, lively, and enthusiastic Dr. Goring it was reserved to discover, in 1827, that the road to perfection lay quite in the opposite extreme-that on the number of rays of light which can be collected by the object lens from every point on the surface of the objects examined, depends the efficiency of the microscope. And thus, to use the words of Dr. Brewster, it has "become quite a new instrument; and promises to be the means of disclosing the structure and laws of matter, and of making as im

portant discoveries in the infinitely minute world, as the telescope has done in that which is infinitely distant."

Dr. Goring's ablest fellow-labourer has undoubtedly been Mr. Pritchard, whose numerous contributions to microscopic science, both instrumental and literary, we have, more than once, had occasion to notice with commendation in our pages. The volume now before us is an "emended (Query amended?) and enlarged edition" of a work under the same title, which appeared in 1829, and helped greatly to make the value of Dr. Goring's discovery known to, and duly appreciated by, the scientific public; but it is an edition so much amended and improved as to be, in fact, almost an entirely new work.

As many persons-not unlearned even -have been heard to express themselves at a loss to understand how it is that an increase in the length of aperture is so efficacious, we shall take this opportunity of extracting the very satisfactory statement of the sufficient reason here given by Mr. Pritchard:

"Every one who has considered the subject at all, will understand that by a series of glasses of different media, aberrations, &c. may be corrected, and almost entirely