scriptions in different tongues, would form ponderous volumes of national biography, whose broad leaves, spread wide before the world, could be read by all wayfarers; serving, at the same time, to correct the public taste, and guide the judgment to a just sense of beauty in design. Copies of the original plates might also be multiplied indefinitely, so as to afford all our provinces and cities fac-simile devices, at a cost little beyond that of the crude material. These monuments to merit, of obelisk type, might be formed, each face separately, and conjoined subsequently to its fellows.

I am, Sir,

Your obedient servant,
J. S. PARTRIDGE.

Bankside, Sep. 7, 1842.

FURTHER REMARKS ON VOLTAIC CUR

RENTS.

Sir,-In calling your attention to the experiments of Aldini for passing a current of voltaic electricity through a great length of water, I had no intention whatever to dispute the ingenuity and originality of the experiments performed by Messrs. Wright and Bain; believing, as Mr. Wright informs you, that they were not aware that the same experiment had been previously and successfully made by Aldini.

However different the apparatus employed in the two experiments, yet the proportionate result is the same; and if the current produced by two square inches of platinum and one square inch of zink was detected by the delicate instruments now in use, it was necessary to employ a greater number of elements in the time of Aldini, as he had no means of detecting a voltaic current, excepting by its power to produce a shock. It is to be remembered, also, that Messrs. Cooke and Wheatstone consider it indispensably necessary to increase the number of elements of a battery in proportion to the length or distance of the telegraphic communication.

With respect to the gradual "dying away" of the electric current alluded to by Mr. Wright, it was discovered by M. Arago that a wire or conductor which has been traversed by a voltaic current continues for a short time in the same

state after the circuit is broken, and produces the same effect as if it formed a part of a direct voltaic circuit. I imagine that Mr. Wright will find that the voltaic current will "die away" gradually as well when the wires are out of the water as when immersed in it. Your obedient servant,

C. W.

TRANSMISSION OF ELECTRICITY-LIGHTNING CONDUCTORS.

Sir,-In the Mechanics' Magazine for August 27, I notice some experiments on the conduction of electricity made by Mr. Thomas Wright. He mentions "a curious and unexpected result," that the magnetism induced by the electric current did not vanish at the moment the electric current was suspended. Perhaps Mr. Wright will have the kindness to inform us, through the medium of your pages, how the induced magnetism was demonstrated, whether in a soft iron horse-shoe magnet, or simply by the action of a coil upon a magnetic needle. If in a soft iron magnet and the keeper was attached, the residuary magnetismn on the cessation of the current of electricity has long been observed. But if a needle suspended in a coil continued to deviate after the current of electricity ceased, it is undoubtedly a newly discovered fact, and one well worthy attention. Mr. Wright would therefore confer a great obligation on all electricians, if he would give a fuller and more explicit account of the experiments than is contained in Mechanics' Magazine, No. 994, and if possible accompanied by a diagram.

In your Number for September 10, Mr. J. R. Hill, in writing on lightning conductors, mentions Mr. Snow Harris's plan, and that of Mr. A. Smith. I beg to say that the wire rope conductor leading from the royal mast-head to the lower mast-head, and from thence to the side of the ship, is a plan brought forward by myself some years ago, and published in most of the scientific journals of the day. Mr. Smith has therefore no claim to the invention. The position I have suggested for lightning conductors on board ships obviates the danger which ships fitted upon Mr. Harris's plan are exposed

to, in consequence of his carrying the conductor through the body of the ship, which is therefore exposed to all the danger of the lateral explosion—a danger Mr. Farraday recently demonstrated, in his usual able manner, to be very great.

Mr. Hill is in error when he supposes that "the electric fluid is conducted over the surface of metallic substances." Mr. Snow Harris also maintained this position for some time, but he has now seen his mistake. Electricity is conducted in a ratio of the mass, not of the surface of the conductor. Mr. Hill is right as to the advantage of continuity in the conductor.

nery, for the supply of which some of the London and country engineers lately entered into competition; and the order for which was given to a country house, because of its tender being the lowest. The consequence of looking to price only in such matters was here remarkably manifested. The castings are such as any London establishment would be ashamed to send out. Wheels with wooden cogs, with eyes to fit on turned shafts! The eyes, too, of these wheels exactly as they were cast-no such thing as boring about them! The key seats also in the rough, as they were cast, neither filed nor cut out by machinery in any way! The metal at the key seats actually drawn in the cooling of the metal, having been cast on mandrels !

The

malleable iron eccentric rods, also, that throw the work into gear, and work into journals of five or six inches diameter, rough from the hammer! In short, the machinery is altogether such as any Lon

don engineer would consider a disgrace to his establishment.

If London engineers are called on to compete with such work, I think it is at least proper that they should clearly understand that it is not to any superiority in workmanship they are to look for obtaining a preference; and that if they desire to have a tender accepted, they have only to make the figure low enough, and then make the work to suit the figure and their own pockets.

I am, yours respectfully,

London, Sept. 16, 1842.

AN ENGINEER.

ON INHALATION AND PERCUSSION.-BY J. HARWOOD, Esq., m.D., f.r.s.

Sir,-Observing that inhalation, when employed by invalids, was performed by the great majority of them either with instruments so unsuitably constructed, or in such a manner as to prevent the possibility of their deriving advantage from the process, I endeavoured, some years ago, so to reconstruct the Inhaler, as to render it a far more convenient and useful auxiliary in the treatment of diseases of the organs of breathing; and I also endeavoured to secure its proper employment, by offering a few very necessary rules for inhaling, which, I am happy to say, have produced much practical benefit, and have been adopted by some eminent members of the profession.

It is now my wish to say a few words, through your medium, regarding percussion as a mode of facilitating the detection of these and some other diseases. As the usual means of percussing, viz., striking the chest with the united extremities of the fingers, in aid of stethescopic examinations, is often equally feeble in its indications, and painful to the emaciated and sensitive patient, like some other practitioners, I have employed in these examinations, during some years, the intervention of a circular disk of a protecting material; and finding this method rendered the sounds of the chest somewhat more clear and sonorous, it led me to the construction of instruments for percussion of small size and of great simplicity, which, without inconvenience to the patient, make the indications of altered structure more ap

parent. They consist of a hammer and one or more lenticular disks of various degrees of thickness and convexity. Though materials of less density and more elasticity, like the parts examined, are in some respects preferable, for greater convenience they are chiefly formed either of ivory or of hard and solid wood, the sonorous qualities of which are obviated by the intervention of a substance affording scarcely any sound of its own. Thus the striking surfaces of the hammer are armed with indiarubber, which I have found it necessary to cut into a pointed form, to prevent the intervention of air between the surfaces struck, the more effectually to diminish external sound. The different degrees of convexity of the disks, which are formed of wood or ivory, or indiarubber, adapt them to the degree of emaciation, and consequent concavities of the surfaces examined, though it is best to accustom the ear to the sounds elicited by one or two only. It is necessary that the disk should be firmly held, and pressed in close contact with the skin when struck by the hammer, that no other sounds be communicated than those produced by internal parts or cavities. And thus, not only within the chest may the sounds of parts examined and deeply concealed be obtained with increased distinctness, indicating the condition of the organs, and facilitating the detection of latent disease; but in dropsical effusions, and some other diseases, I employ this percussor with interesting effect and advantage.

Having used these instruments since the early part of the year 1840, ample opportunity has been afforded of proving their advantage; and I have placed patterns of them in the hands of Mr. Waugh, of Regent-street, in the hope that they may continue to be properly constructed, and thus rendered useful to others as well as to myself.

From, Sir, yours respectfully,

JOHN HARWOOD.

West Villa, St. Leonard's, Hastings,
September, 1842.

weights in different parts of my coal yard and on my wharf, I find that exposure to the weather, and the accumulation of dirt in the raised figures and loops of the lifting rings, cause the weights to be inaccurate. When the Leet Jury visit

me twice or thrice a year, I am almost sure to be mulcted for some weights being too light by abrasion or casualties, whilst others are too heavy from dirt and compacted coal dust. I should be thankful if any of your ingenious correspondents would advise me how to keep my weights correct, or devise some means of weighing from 1 cwt. to 5 cwt. of coal. by a graduated lever on the principle of the steelyard. The weighing machine must be light, and moveable on small wheels, so that it may be removed from one coal-heap to another with facility, as we have sometimes three or four carts all waiting at the same time; it should also be low and flat, for the convenience of holding the bags whilst the coals are shovelled up. Our bags hold ten stones, which is as much as a man can ordinarily lift into his cart. I have been at great expense in providing good weights and weighing machines, and have as many as sixty weights of 28 lbs. each in use, and I am sorry to say that the rough usage to which they are exposed in the open air, with the removal in and out of boats, subjects me, unavoidably, under present arrangements, to the disagreeable circumstance of being fined by the jury; although the deviation of the weights is often to my loss, and not a dishonest gain, as some ill-natured persons are apt to infer. It costs me 8d. per weight of 28 lbs. to have them verified by the Inspector of weights and measures, who lives a long way off; and to remove such heavy articles in a cart has on several occasions caused them to be injured, and to be inaccurate immediately on having them adjusted.

What I want is a weighing machine for heavy commodities, without weights, or at least but one, for coals, linseed cakes, iron castings, and other bulky heavy goods, weighed on the wharf. I am yours respectfully,

A WHARFINGER.

COAL WEIGHTS.

Sir,-Being a dealer in coals, and my trade requiring a great number of 28 lb,

manner, and has cast round it four square rods, bb bb, forming guides for the ballvalve, c, preventing its escaping when not pressed up into its seat by the leverrod, d, which is jointed to an ear at e, cast on the cock; to the other end of the lever is affixed the copper float, f, which may be either a whole or half ball. A stop is provided at the jointed end, to prevent the lever falling so low as to allow the ball, e, to escape from the cage, bb bb, but yet sufficiently low to permit the escape of as much water as the service pipe can supply.

may

The action is sufficiently obvious, but be briefly described as follows:-When the water in the cistern falls, the float, f, will fall with it, until stopped by the stop at e; the ball-valve, c, being no longer held up in its seat, will fall, and allow the water to rush in, as soon as it is laid on in the pipes; as the cistern fills, the float fwill rise, and raise up with it the lever-rod, d, and valve, e, and press the latter tight into its seat, thereby preventing any more water entering. A small cup, m, is shown on the lever-rod, to receive the ball-valve, and prevent its getting bruised. The side view, fig. 1, shows the cock when closed; and the section, fig. 2, when it is open. In the former, the dotted line represents the level of the water when the cistern is full.

A hemispherical valve might be used instead of a ball, but it would require a spindle and joints, to prevent its turning round: or even a conical valve might be employed, care being taken to insure its rising truly into its seat; but the spherical valve is much to be preferred.

Sticking, which continually occurs with the common cock, (unless it is so loose as to leak,) can never, it will be observed, occur with mine. The diminished water-way, occasioned by the perforation in the plug being so much smaller than the bore of the pipe, is also obviated in this; since, by allowing sufficient play to the ball-valve, the cock will allow as much water to pass through it as the pipe can supply to which it is affixed; and the cistern, accordingly, will be filled in much less than the usual time. I remain, Sir,

Your obedient servant,

August 29, 1842.

E. M. J.

TAMPING WITH SAND, AND FIRING POWDER BY GALVANISM IN BLASTING ROCK.

Sir,-In doubtful matters, theories and opinions may be very erroneous; but facts in such cases must be of value. Mr. James T. Wilson, in your No. 989, treats my remarks on tamping with sand as "Theory versus Practice," in

which I think he is in error.

In an interesting paper on firing charges by galvanism in No. 978, it is stated to be the belief of Mr. Roberts, that "many hundred weight of gunpowder would be required to blow out a column of sand of two inches diameter and 18 or 20 inches in depth, placed in solid rock."

I asserted on the contrary in No. 983, that instead of requiring many hundred weight, a single ounce of powder would blow out every particle of the sand.

I ventured an opinion as to the cause of this fact; that opinion might be good for nothing, but still the foundation was the positive fact, and not a theory on which a result was presumed, as would seem to be implied by Mr. Wilson in calling it "Theory versus Practice."

Now I will mention another fact, founded on numerous trials.

In a hole of 1-inch diameter and 2 feet deep in solid rock, one quarter of an ounce of powder will blow out every particle of sand filled over that charge to the very top of the hole; while 3 oz. will not disturb a well-hammered clay tamping in a similar hole; and the relative effects will be nearly the same in larger holes with increased charges.

With these facts before us, I think the presumption is that for tamping, sand is far inferior to the tamping of clay or broken brick hammered down in the usual manner.

It is quite true that the effect of the explosion in splitting the rock is very rapid, and with tolerably large charges, will operate in that way quicker than it can force good tamping out of the small opening by which the charge is introduced; but where the sand shows such a great want of resistance as above described, it is impossible not to suppose, but that it is incapable of procuring the maximum effect from the explosion; and in small charges the loss must be very great.