Remarks.-The correction of the indications of the mariner's compass in iron vessels is, it appears, a process of such extreme delicacy, and such fearful risks are connected with it, that nautical men must not be entrusted with it. However that may be, in regard to Mr. Airy's method, the following mode occurs to us of so simple and practical a character, that no difficulty can attend its adoption. Though it is applicable only under certain circumstances of locality, yet these are likely to occur in cases where it is most required, and the important interests which are attached to an accurate correction available in all latitudes, may warrant a voyage in a great degree for the express purpose. It is likewise wholly devoid of scientific pretension, but it may not be the less useful on that account, and we should be glad to see opinions on it from some of the able nautical correspondents of this Magazine.

Let the circumstance of the vessel being in some situation on or adjacent to the magnetic equator be taken advantage of to ascertain the deviation of the needle for each point of the compass. Now this disturbance may be considered to be due solely to the permanent magnetism of the vessel, for its induced magnetism is neutralised by its geographical position. Let the process be repeated in a higher latitude; the differences of deviation then found is to be ascribed to the induced magnetism, and the proper position for Barlow's plate in respect to the compass is to be determined in the usual manner, but so that it may compensate (or indicate as may be thought proper) those differences only. Now, as the permanent magnetism is constant for all latitudes, and as its effect has been ascertained separately for every point of the compass, it is easy at any time, by making allowance for it, to obtain the necessary additional correction, and thus the perhaps precarious security of the correctors will not be required, and the delicate operation of correcting the deviation is dispensed with. The deviations, as ascertained for any particular place, cannot be used for every other, or for any other place, except within certain limits, but they must be determined as they are required to be known, and by a reference to the separate amounts of disturbance, as due to the induced and the permanent magnetisms; for although the latter continues the same, the former differs with the different latitudes, and has its poles reversed on opposite sides of the magnetic equator, and hence arises the necessity of having Barlow's plate, in addition to the data of correction already provided, either to act as a continual corrector of this varying influence, or as means whereby at any time its amount can be ascer

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tained and the necessary additional allowance made. If perfect dependance can be placed on Mr. Airy's method of obtaining a due estimation of the separate causes of disturbance, why not allow for the error occasioned by the permanent magnetism, instead of attempting the delicate operation of correcting it; but probably the correction in practice is somewhat of a mixed and equivocal character, sometimes partaking unduly of one magnetism and sometimes of the other, and therefore this more certain course, of making allowances, is not available by his method; and hence also may be conjectured the reason of the alleged nicety of the process. The entire or conjoint effect may, notwithstanding, be accurate for the place, and sufficiently so for voyages, if confined to latitudes not differing much from that in which the correction is made. The natural variation of the magnetic needle, and as being different in different places, has not been adverted to, but the influence of these circumstances would not, of course, be neglected when they were required to be noticed. Not having any practical acquaintance with the subject, we submit these observations with much deference to those who are in this respect qualified to offer an opinion.

NOTES AND NOTICES.

Hail Storm Preventing.-M. Arago has proposed a plan for discharging clouds, in cases of storms, of the electric fluid which they contain, and thus preventing the frequent occurrence of hail storms, which, as is well known, are generally produced by two currents of clouds, charged with positive and negative electricity, crossing each other. It consists in an improvement upon Franklin's experiment of the kite, with which he obtained an electric spark from a cloud, and afterwards Dr. Romas, of Nerac, and Messrs. Lining and Charles, of the United States, produced electric flashes three and four feet in length. M. Arago recommends that a small balloon, properly secured, armed with metallic points, and cominunicating with the ground by a rope covered with metallic wire, like a harp-string, should be kept permanently floating in the air at a considerable height over the spot which it is wished to preserve from the effects of lightning or hail; and he expects that by such an apparatus as this a cloud might have its electric contents entirely drawn off without any damage being caused, or that at least the intensity of a hail storm would be greatly diminished. The experiment is so simple that it is well worthy of a trial.-Galignani's Messenger.

Timber Steamers v. Iron.-The following challenge is published in the present month's number of the Nautical Magazine :-"Mr. Editor,-Having read another account of iron steam-boats in your journal, I think it right to disabuse the public mind as regards the great speed attributed to those vessels over timber-built ones; and particularly to deny the fact attempted to be foisted upon the public, that the Rainbow iron steamer, is the fastest vessel afloat. I have now commanded for three seasons an oak built steamer, in the Thames, built and equipped in London, of 100 horses' power only (the Rainbow is 180 horses' power); and I hereby challenge the above-named iron vessel, for a run from London to Margate and back, for 200 guineas; indeed I

have had this money now subscribed and in my hands for the last eighteen months, for the purpose of running my vessel against any iron or wooden steamer afloat, whatever may be the power or dimensions. I have challenged the wonderful Rainbow repeatedly, but they always gave me a wide berth. 'Tis true they once tried their strength with one of our little clippers, the Vesper, of 60 horses' power, and the Rainbow, of three times the force, actually beat this little ship three minutes from Blackwall to Gravesend! 1 trust by your inserting this in your valuable Magazine, that it will put a stop to the further boasting and puffing of the builders and engineers of the iron boats, as I am quite convinced that there are plenty of builders and engineers too, in London, who will equip a good timber-built steamer to beat in speed and be much stronger than any of the new-fangled iron steamers. "R. LIGHTFOOT,

"Captain of the Ruby Gravesend steamer. "P.S. Should any one take a fancy to match the Rainbow or any other steamer against my vessel, I am always to be found at the Albion, Gravesend, and I will pay down 501. deposit for the race."

Use of Geology to Farmers.-One of the most obvious sources of advantage to the farmer from an acquaintance with the distribution of mineral masses, is the facility with which, in many instances, the injurious effects of small springs coming to the surface may be obviated. The theory of the earth's internal drainage is so simple, that every man of common sense would be able to drain his lands upon sure principles, or else to know precisely why it cannot be drained, if he were to become so much of a geologist as to learn what rocks existed under his land, at what depth, and in what positions. Springs never issue from stratified masses, except from reservoirs somehow produced in jointed rocks, and at the level of the overflow of these subterraneous cavities. Faults in the strata very frequently limit these reservoirs, and determine the points of efflux of the water. Let those faults be ascertained, or the edge of the jointed rock be found, the cure of the evil is immediate. But some geological information is needed here; and landed proprietors, who think it less troublesome to employ an agent than to direct such a simple operation, may at least profit by this hint, and choose an agent who knows something of the rocks he is to drain. Another thing, probably of importance to agriculturists, is the discovery of substances at small depths, which, if brought to the surface, would enrich, by a suitable mixture, the soil of their fields. This is very strongly insisted on by Sir H. Davy in his essays, and considering how easy a thing it is for a landowner to ascertain positively the series of strata in his estate, it is somewhat marvellous that so few cases can be quoted, except that of Sir John Johnstone, Bart., of Hackness, near Scarborough, in which this easy work has been performed. Finally, in experiments for the introduction of new systems and modes of management, with respect to cattle and crops, it will be of great consequence to take notice of the qualities of the soil, substrata, and water, for these undoubtedly exercise a real and perhaps decisive influence over the result.-Mining Review.

Steam Boat Disasters in America.-New York, March 2.-The following is a list of the steam-boat disasters which occurred on the western rivers during the year 1838-37 steamers snagged, 14 blown up and collapsed, and 29 more or less injured; total 80 steam-vessels. Of the above, 34 were total losses, besides four that could not be repaired. Of the 37 snagged, but four were on the Ohio; and of the whole number, 50 were on the lower Mississippi.

Arsenic.-M. Orfila has discovered a method of detecting the smallest atoms of arsenic, even when administered in solution. For this he used a lamp, the hydrogen gas of which was produced by a piece of zinc, steeped in diluted sulphuric acid, The arsenic, however small the quantity, when exposed to the flame of this gas, is carried along by it, and if a cold substance be presented to the end of the narrow tube conveying the flame, the arsenic will be deposited on it like a spot.

The Society of British Artists announces a series of conversaziones to be held on alternate Saturday evenings, commencing April 6th, to which strangers are to be admitted on payment. The plan includes not merely the exhibition of the pictures, but also the delivery of lectures on artistic subjects: and if well carried into effect, is worthy the consideration and patronage of all who do more than talk about

art.

Light Painting. The announcement of Daguerre's discovery has turned the brains of half the world: you sober English have certainly not escaped the infection; and the speculating Germans, as you have noticed, are hard at it. I learn, by letters just received from Munich, that Profs. Steinhel and Robel are astonishing the natives with their Photogenic pictures. It is said that they have discovered the process of M. Daguerre, but it seems to me more than probable that their process rather resembles that of Mr. Talbot; and that by their invention pictures can be obtained not only with the aid of the camera obscura, but by the direct agency of light, so that they take, in an instant, copies of pictures traced upon blackened glass. [No doubt the process here indistinctly referred to is the same as, or similar to, that of Mr. Havell.] Daguerre's pictures are, it is known, traced upon copper [], but Messrs. Steinhel and Robel imprint theirs upon paper. Several experiments are stated to have been made in presence of a crowd of spectators, and to have been in every instance successful.-Ath.

City Greenhouses.-A plan has lately been discovered for keeping green plants in a fresh and lively growing state, in all seasons and climates, with a very small degree of trouble. It is, I suppose, generally understood that greenhouse plants, among which may be numbered many flowering tender herbs, will not grow in the open air in a town, or even in a carefully kept room. Besides being deprived of pure air, the plants are not properly and regularly watered. Watering only now and then does not suit all kinds of plants; many require to live in an atmosphere from which moisture can be at all times drawn. The new and improved method consists simply in the use of a glass case for the plants. The case may be the size of a room, or of a box-it is all one. The top and sides of the case are of glass frames; the bottom contains earth in which the plants grow; the whole is kept closed, except at short intervals, when a small door is is opened for any necessary purpose. The case may be placed in a room at a window full in the sun's light, or if the enclosure be large, like a greenhouse, it may be situated out of doors. The plants being set in the usual manner, the earth is saturated to a certain extent with water, and the case closed. Nature now takes upon itself the entire management of the process. When the sun shines on the case, the moisture rises in a natural evaporation from the earth, and hngs in condensed globules on the inside of the glass. When the cold of evening ensues, the moisture descends, and is ab. sorbed by the plants and by the earth. Thus alternately rising and descending, the moisture in the case keeps up a proper and regular system of irrigation, wherebythe plants are sustained in a state of great freshness and beauty.

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BURSILL'S MINER'S CONDENSED-AIR LAMP AND BREATHING APPARATUS.

The Society of Arts lately awarded a asilver medal to Messrs. G. and W. Bursill, of Islington, for an improved safetylamp, which has about it some novel and ingenious features. The principal objections to the invention are its complexity and weight, which we fear will be found so insurmountable as to prevent its use in the working of mines, although it would doubtless, be found useful for explorations. We extract the following description from the last part of the Society's Transactions.

"The object of this invention is to apply condensed atmospheric air to the double purpose of supplying the lamps of miners, and of affording to the miners themselves, in particular emergencies, pure atmospheric air for breathing, while exploring those parts of a coal mine that may happen to be rendered hazardous to life, from the quantity of carbonic acid and other unrespirable gases that they may contain.

"This lamp is completely insulated from the mine, the flame being enclosed in air-tight fittings, and its combustion being supported by fresh atmospheric air condensed into close vessels, and then brought down into the mine. The foul air from the lamp is expelled into the mine in a perfectly secure manner; for though it can no longer support combustion, and has nothing in its nature that can communicate light to the external air; yet it is doubly guarded; first, by passing through wire gauze, and then having to bubble through water. Thus the bare possibility of a spark from the flame passing the chimney, is totally prevented.

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Fig. 1 represents the lamp, with the reservoir and the tube which connects them together. a is the oil vessel of the lamp, over which is screwed the cap or dome b, having a central aperture, in the middle of which the burner or wick holder just rises through: in the opposite sides of this cap are fixed the two cocks, c c. The body of the lamp dd, with a lens e in its side, is screwed into the cap b. On the top of this are laid two or three plates of wire gauze, f, over which is screwed the chimney g; the end of this chimney is bent downward, and is surrounded by a vessel h, to contain water, into which the end dips.

is part of a vessel made sufficiently

strong to hold condensed atmospheric air; this it gradually imparts to the lamp through the screw cock j, flexible tube h, and cock c, from which it passes under the cap b to its central opening, where it enters the lamp close around the flame. is another screw cock from the air vessel, with a flexible tube m, the end of which is furnished with a mouthpiece n, from which the workman, in case of emergency, can obtain a breath of fresh air.

"In order to supply the lamp uniformly with air, it is made to pass through a very small opening at first when highly condensed, and this aperture gradually enlarges as the pressure lessens.

"Fig. 2 is a section of the screw cocks jb, to show their peculiar construction. The screws j and I have cylindrical portions passing through collars of leather to keep them air tight; their conical points shut or open their respective apertures. The cock opens directly into the vessel i through the aperture o. The cock j is the one from which the lamp is supplied, it therefore has a selfregulating aperture attached to it. The aperture of the cock enters the chamber p, made large enough to contain a spiral spring; at the bottom is another opening q, into which is nicely fitted the cylindrical plug r, as air tight as possible consistently with sliding freely; on the top of this is a disk, on which the spiral spring that fills the chamber p acts to thrust out the plug r. In the side of this plug is made a groove, as shown in the figure, very small at the lower end, and as much larger at the upper end as the lessening pressure will require to let the air escape at an equal rate from first to last.

"The strength of the spiral spring, and diameter of the plug r, are made to correspond with the intended condensation of the air. Whilst the cock j is shut, the spring can keep the plug r down, as here shown; but as soon as the cock is opened, the difference of pressure between the external and internal air, pushes up the plug r, notwithstanding the resistance of the spring, leaving only the smallest part of the groove exposed for the air to escape through; but as the pressure lessens by escape of the air, the spring becomes able to protrude more of the plug r, and thus present a large portion of the aperture, through which a larger portion of air may pass :

thus a tolerably equal supply of air will be given from first to last.

"When the vessel i is nearly exhausted, another vessel is connected with the other cock c, fig. 1, ready to be let on before the other is taken away."

THE LONDON FIRE BRIGADE. "Oh! what shall we do?" the bold Fire King said, As he sat where the 'Change should have been, "They've attack'd our good friends of the London Brigade,

"Was ever such impudence seen ?" Then up spoke a vassal, a vet'ran at court,

"A way out of limbo I spy,

"Our champion shall swear his old Fire Report "From beginning to end was a ——," "Fie !" "Oh, fie!" cried the chief, in a voice far from sweet,

Though his eye sparkled bright at the fun,"If to make out a case his own words he must eat, "The job will be Baddeley done!"

Sir,-Curtius himself could not have had a stronger feeling for the weal of Rome than your worthy correspondent Mr. Baddeley, for the reputation of the Fire Brigade. Rather than the slightest discredit should rest upon their efforts, he is willing not merely to admit, but to assert, that the Reports on London Fires, which he furnished to the Mechanics' Magazine, previous to the establishment of the brigade, are- - (how shall I phrase it?)-not to be depended upon. A stronger instance of what may very properly be called self-denial, could not easily be imagined. If any one else had ventured on such a charge, Mr. Baddeley might well have been expected to hold himself an insulted individual; but what is to be said when the accused and the accuser meet in one and the selfsame person? If we would avoid insinuating that Mr. B. made one very incorrect assertion last week, we must per force allow that he made a great many some time ago! From this dilemma there is no escape.

But even admitting all that Mr. Baddeley himself can wish for as to the unfounded nature of his own reports for by-gone years, there is enough in the last one alone to overthrow the wholesale assertion as to the "increased comparative security of lives and property" under the new system. What are we to think, for instance, of the inconsistency, which he has not attempted to explain away, of filling up an article containing "such a list of total losses as

35

has seldom before occurred," with enthusiastic praises of the successful exertions of the brigade? Ever since the establishment of that body, Mr. Baddeley has been most abundantly supplied with materials for his reports; great and disastrous fires have, as every one knows, abounded to an unprecedented extent; and yet Mr. B. has never been weary of congratulating them on the "success" of their exertions. This seemed rather an inconsistent process, until Mr. B.'s letter appeared, taunting the Parisian firemen with their want of success in having had only one great public building burnt down in a whole series of years. This letter seemed to throw great light on Mr. B.'s notions of the duties of firemen, and to clear up the mystery as to his formerly incomprehensible trumpetings of the fire-brigade, in the same breath with long and terrific details of the progess of unchecked calamity. Mr. Baddeley, indeed, objects to this appliIcation of his views, but as he does not condescend to say why, I need not take the trouble to guess: he may depend upon it that the position he took up in reply to Mr. Simeon is the best one after all if the extent of damage done under their "protection" be taken as the touchstone of success, the brigade will be pretty certain to come off triumphant.

:

The present occasion is not the first in which Mr. Baddeley has "turned his back upon himself" when the subject of fire insurance was in question. Time was that he held, and held most firmly, the opinion that no highly-efficient system of fire-police could be expected while the matter was left entirely in the hands of the insurance companies. Now, the perfection of the brigade system, and its "high efficiency," are his neverending themes; many are the contradictions given him, not only by his repudiated reports, but by facts that would have stared us in the face just the same as if his reports had never seen the light. How is it that this "change" has " come o'er the spirit of his dream?" Whatever the cause, certain it is that his opinions on this point have been completely revolutionized since the praises of Braidwood and his brigade have become his constant care. He may coolly assure us, perhaps, that the opinions advanced in his unfortunate re

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