any convenient distance from the points G and e, describe the intersections men, and draw the line m n n until it touch the diameter of the base produced, and the locus of that point is the centre, from which draw GG', the epicycloid generated by the motion of P2. This method will apply to P1, or any other case of determinate ratio between the generant and the base.

From the principles of construction herewith adopted, we conclude, that in all cases, when the generating circles are to each other in a ratio greater than two to one, the interior epicycloid will be concave to the base circle on which it rolls; and when the ratio is less than two to one, it will be convex to the base. But when the proportion is that of 2:1 (exactly, in that case only) the epicycloid is a straight line, equal radius of base. H. S. RAYNER.

Sir,-The captain says, "that 61b. per inch was all the pressure they worked at; and yet they found great difficulty in procuring steam." He also says,,

"that the other boiler was red hot, and without water!" Here is a frightful state to be in. If it was found the pumps did not supply sufficient water to work at 6lb. per inch, why not lower the pressure and decrease the intensity of the fire, so as to work at 4lb. per inch?

The engineer ought to have known, that in proportion as the density or expansibility of steam is increased, so is the quantity of water taken up by the caloric it contains. For instance, steam at atmospheric pressure is as 1711 to 1 of water, but as 1.17 atmospheres, its force is increased to 2.44lb. per square inch, and contains 8 grains per cubic foot of steam, more water than before, and so on in proportion.

Now, suppose the pumps were set (on starting from Hull) to supply water to the boilers under the pressure of 4lb. per inch, is it not egregious folly to expect them to deliver water sufficient to work at 6lb. to the inch, unless the length of the stroke is increased so as to

deliver a proportionate quantity of water? For, as I have before stated, and it ought to be universally known, that the higher the pressure the greater the quantity of water and latent caloric is absorbed or taken up by the steam; consequently it is of the first importance to be very careful in regard to the pumps being of a fit and proper size, and kept in the best possible order for supplying water according to the intensity or expansibility of the steam, or the evaporation required. It would, perhaps, be easy to show, that the pumps at starting did supply sufficient water; but by increasing the evaporation without altering the stroke of the pumps, the water kept decreasing in the boiler continually during the twentyfour hours voyage from Hull, until it evaporated nearly to zero; when, of course, as the intensity of the fire was not diminished, but, perhaps, increased, the flues would become red hot, and then the water from the pumps would in such case naturally flash into steam; and the safety valves of all boilers being much too small to discharge so large a volume of steam formed instantaneously, an explosion must of course take place. The stronger the boiler under such negligent circumstances, the more disastrous will be the effect, as was the case of the Union at Hull not long since, and which, I was satisfied at the time, bursted from want of water, and neither from bad iron nor defective workmanship.

If the public would attach less weight to the opinions of those learned M.D.'s, D.D.'s, L.L.D.'s, and other paper and pasteboard artists and evidence-mongers, who are so fond of calling themselves engineers, and put a little more trust in practical manufacturing engineers and boiler-makers, it would be a public benefit; for one practical fact is worth a hundred theoretical opinions, filled and interlarded with ifs, and buts, and suppositions.

No doubt a host of the above theorists will be ready to come forward with their opinions on the present occasion, and will be thrust forward by their various partizans and admirers accordingly, to the exclusion of those practical men whose opinions ought to have greater weight than is attached to them in general.

Now, it would be very easy to find a remedy for such unfortunate occurrences

as those of the Victoria and others, and that is by attaching a glass guage to every boiler, such as are affixed to the patent boilers of Upton, Nicholls & Co., of Battersea.

If this instrument had been attached to the boilers of the Victoria, any one on board might have seen the water and steam in the boilers by a glance, the water and steam being always visible; for if the water was a hair's breadth higher or lower than the proper level assigned, it would be visible, not by any index or other uncertain guage, but the water itself is seen in its boiling state, and the steam inside the boiler also.

Any person desirous of directing their sight to this safe, neat, and most important little instrument, could, on perceiving the water decreasing below its assigned level in the boiler, say instantly, "Stop the engine, open the safety valves, and lower the fires; the water guages show the pumps are deranged," &c.

At the same place may be seen one of the safest boilers, and the quickest in getting up steam, that has yet been invented; and which is by far the best for a ship, inasmuch as it is smaller and lighter, and, by not carrying the water in one boiler, but in several compartments, safe beyond all comparison.

This boiler would do well at sea, if external condensation was adopted; and it could be very easily repaired if required, even at sea. As to its saving properties, a ten-horse power one has been known to produce steam of 45lb. to the inch in fifteen minutes, and the boiler is proved to bear a pressure of 1000ths to the square inch.

A rupture in such a boiler could not be attended with any bad consequences. If any rent was to take place, as those of the Victoria, and the Union at Hull, it would only put out the fire. Nor is it possible for it to explode altogether, and disperse the water instantaneously, as is the case with all those boilers which carry their water in bulk.

Now, so long as the owners of steamers continue to follow the plan of rejecting the best boilers and engines for the sake of getting the lowest priced ones, and which are the least to be depended on, the public must expect to have their lives put in jeopardy.

Even the simple water guage abovementioned would have prevented all

those disastrous effects that have hap pened both in England and America. In fact, Mr. Editor, no boiler, whether for sea or land service, ought to be suffered by the owners to work without it, let the boiler be whatever shape or make it will.

Now, as all common boilers are liable to similar accidents, I would strongly urge the necessity of fitting them up with large and very capacious safety valves, capable of allowing the escape of much greater volumes of steam than is at present the case. Besides which precaution, a metallic alloy, fusible at any number of assigned degrees of heat, might and ought to be used on board of every steamer. This being appended to the lever of a very capacious valve, would, by allowing the steam to escape, prevent the bursting of every kind of boiler. This was mentioned to me by Mr. Upton as the plan to be adopted by them for all sea-going boilers.

I am, Mr. Editor,

Your obedient servant,
SCRUTATOR.

MILLS'S MERCURIAL PUMP. Sir,-Some time since I constructed a mercurial pump, on what I conceive to be a new plan. I presented a working model to Mr. Grier, lecturer of Natural Philosophy in the Baronial Hall, who exhibited it to his class, and the action was so satisfactory to the lecturer and his audience, that I have been solicited to transmit you an account of the pump, which I hope you will not consider unworthy of notice in your excellent periodical.

The pump is of the suction kind, A A is a pipe not more than 30 feet in length, open at both ends, the undermost of which is inserted in the well to be drained. At B there is a clack valve opening upwards, immediately above which a branch pipe C leads off, and opens into an air vessel D, of the ordinary construction. The top of the pipe C is furnished with a valve E, opening upwards into the air vessel, and the ejection pipe is terminated at the required height F. Immediately above the branch pipe C, the main pipe A A is begirt with a cylinder G G of iron or glass. The cylinder is of greater diameter than the

A A, which enters the well; but the cylinder I being lifted by the handle K, yet not so far as to come out of the mercury, the air within the pipe A A will be rarefied, and the pressure of the atmosphere will force the water from the well up the pipe A A, so as to pass the valve B, which opens for its passage. When the cylinder I is brought down, the valve B shuts, the air is compressed, and the water having no other way of escape, passes through the tube C, through the valve E, and into the air vessel D, thence up the pipe and becomes discharged at the orifice F.

The advantage of this pump is, that little friction is encountered, and for every inch of stroke of the handle K, the water will be raised one foot high. JAMES MILLS.

Glasgow, 13, Clyde Terrace,

March 30, 1838.

AMERICAN STEAM-BOAT RACES.

**That these steam-boat accidents mainly arise from a headlong impetuosity, and childish rivalry, seems clear enough. The Ben Thersod caught fire in running a race. The American public ought to put down this practice on the contrary, it is sanctioned, and stimulated by paragraphs like this:"There was a beautiful trial of speed last night between the steam-boat Swallow and Rochester, which are undoubtedly the two fastest boats in the world. They came out

of their berths in New York together, and for twenty miles ran neck and neck, neither gaining or losing a foot." This voyage, which is about 150 miles, appears to have been made in between eight and nine hours! We have, in another paper, a description, by a passenger on board the Franklin, from Louisville up the Ohio to Cincinnati, of a race carried on the whole of that distance, which is also about 150 miles, by this boat with a rival one, named the Phillips. In this case, there was a wager of 100 dollars between the captains that the Franklin would beat by an hour. The other boat had a half-hour's start. At fifty miles she was nearly "over-hauled;" at thirty more she was passed (having slight stoppages to make with the mails), but by only five or six lengths.

The passengers of the leading boat, some sixty, including ladies, now entered into the sport, which they had hardly understood before:-"The contagion spread -Go, ahead, captain-keep her in the wake-huzza for the Phillips !' was in every mouth. Nothing could exceed the spirit of the firemen and deck hands. The hatches were thrown open, pine knots covered the

deck, and two or three axes kept going in splitting and breaking them; the deck passengers were huddled into the bow, to give the boat more dip; the chain waggons were hauled from the tops of the chimneys, while dense clouds of black smoke filled the atmosphere over us. It was plain that no less excitement prevailed on board the Franklin. Thus far she had been queen of the waters." And so they keep on for the next twelve or fifteen miles. "In passing Warsaw, the two boats were 'neck and neck,' and we were saluted with loud and continued cheers. No response was sent back from either boat-not a sound was heard save the sonorous breathings of the scape-pipes, and the whirl of the waterwheels."-After this, "the boats, which till now had been abreast, and from ten to fifty feet apart, struck each other with a slight concussion. The ladies, of whom there were twelve or fifteen on board the Phillips, became alarmed, and besought their husbands to interfere. While this consternation prevailed in the ladies' cabin and state rooms, a different scene was witnessed without: the two boats seemed to be lashed together, the officers of each shaking hands across the railings, and the firemen and crew looking defiance. The river in front of the boats, from the light of the furnaces, seemed a sheet of fire, while the sky continued overclouded with the dense volumes of smoke which poured forth from the chimneys. In passing Petersburgh, the boats again struck with a more violent concussion than before; the alarm of the ladies increased," and so on. Now, what

an atrocious game is this to be played with human life! That the passengers encouraged it, only aggravates the case; and so do the cheers from the shore. We fear that the Americans are too careless of life. Their driving habits of business, and the adventurous frontier character of a part of their population, may account for it. The great number of their steam-boats has familiarized them with scenes such as we have here described. Think of more than forty boats on Lake Erie alone-of nearly 400 on the Mississippi-for it must be allowed, as we said of the burning of buildings, that the Americans are as enterprising in one way, as destructive in another. But none of these circumstances can excuse the practices referred to, though they go some way to account for them. On the contrary, great number of the steam-boats, and the usual comparative lightness of their construction, is the strongest argument for a more careful management on board, and for the interference of the public and the government.-Athenæum.

M8

the