Chapter 4

_First_.--You will observe that, relatively to the center, a revolving body, at any point in its revolution, is at rest. That is, it has no motion, either from or toward the center, except that which is produced by the action of the centripetal force. It has, therefore, this identity also with a falling body, that it starts from a state of rest. This brings us to a far more comprehensive definition of centrifugal force. This is the resistance which a body opposes to being put in motion, at any velocity acquired in any time, from a state of rest. Thus centrifugal force reveals to us the measure of the inertia of matter. This inertia may be demonstrated and exhibited by means of apparatus constructed on this principle quite as accurately as it can be in any other way.

_Second_.--You will also observe the fact, that motion must be imparted to a body gradually. As distance, _through_ which force can act, is necessary to the impartation of velocity, so also time, _during_ which force can act, is necessary to the same result. We do not know how motion from a state of rest begins, any more than we know how a polygon becomes a circle. But we do know that infinite force cannot impart absolutely instantaneous motion to even the smallest body, or to a body capable of opposing the least resistance. Time being an essential element or factor in the impartation of velocity, if this factor be omitted, the least resistance becomes infinite.

We have a practical illustration of this truth in the explosion of nitro-glycerine. If a small portion of this compound be exploded on the surface of a granite bowlder, in the open air, the bowlder will be rent into fragments. The explanation of this phenomenon common among the laborers who are the most numerous witnesses of it, which you have doubtless often heard, and which is accepted by ignorant minds without further thought, is that the action of nitro-glycerine is downward. We know that such an idea is absurd.

The explosive force must be exerted in all directions equally. The real explanation is, that the explosive action of nitro-glycerine is so nearly instantaneous, that the resistance of the atmosphere is very nearly equal to that of the rock; at any rate, is sufficient to cause the rock to be broken up. The rock yields to the force very nearly as readily as the atmosphere does.

_Third_. An interesting solution is presented here of what is to many an astronomical puzzle. When I was younger than I am now, I was greatly troubled to understand how it could be that if the moon was always falling to the earth, as the astronomers assured us it was, it should never reach it, nor have its falling velocity accelerated. In popular treatises on astronomy, such for example as that of Professor Newcomb, this is explained by a diagram in which the tangential line is carried out as in Fig. 1, and by showing that in falling from the point A to the earth as a center, through distances increasing as the square of the time, the moon, having the tangential velocity that it has, could never get nearer to the earth than the circle in which it revolves around it. This is all very true, and very unsatisfactory. We know that this long tangential line has nothing to do with the motion of the moon, and while we are compelled to assent to the demonstration, we want something better. To my mind the better and more satisfactory explanation is found in the fact that the moon is forever commencing to fall, and is continually beginning to fall in a new direction. A revolving body, as we have seen, never gets past that point, which is entirely beyond our sight and our comprehension, of beginning to fall, before the direction of its fall is changed. So, under the attraction of the earth, the moon is forever leaving a new tangential direction of motion at the same rate, without acceleration.

(_To be continued_.)

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COMPRESSED AIR POWER SCHEMES.

By J. STURGEON, Engineer of the Birmingham Compressed Air Power Company.

In the article on "Gas, Air, and Water Power" in the _Journal_ for Dec. 8 last, you state that you await with some curiosity my reply to certain points in reference to the compressed air power schemes alluded to in that article. I now, therefore, take the liberty of submitting to you the arguments on my side of the question (which are substantially the same as those I am submitting to Mr. Hewson, the Borough Engineer of Leeds). The details and estimates for the Leeds scheme are not yet in a forward enough state to enable me to give them at present; but the whole case is sufficiently worked out for Birmingham to enable a fair deduction to be made therefrom as regards the utility of the system in other towns. In Birmingham, progress has been delayed owing to difficulties in procuring a site for the works, and other matters of detail. We have, however, recently succeeded in obtaining a suitable place, and making arrangements for railway siding, water supply, etc.; and we hope to be in a position to start early in the present year.

I inclose (1) a tabulated summary of the estimates for Birmingham divided into stages of 3,000 gross indicated horse power at a time; (2) a statement showing the cost to consumers in terms of indicated horse power and in different modes, more or less economical, of applying the air power in the consumers' engines; (3) a tracing showing the method of laying the mains; (4) a tracing showing the method of collecting the meter records at the central station, by means of electric apparatus, and ascertaining the exact amount of leakage. A short description of the two latter would be as well.

TABLE I.--_Showing the Progressive Development of the Compressed Air System in stages of 3000 Indicated Horse Power (gross) at a Time, and the Profits at each Stage_

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Gross | 3000 | 6000 | 9000 | 12,000 | 15,000 | Indicated | Ind. | Ind. | Ind. | Ind. | Ind. | Horse Power | H.P. | H.P. | H.P. | H.P. | H.P. | at Central | | | | | | Works: | | | | | | -----------------------------------------------------------------------------

Thousands of | 1,080,000 | 2,160,000 |3,240,000 | 4,320,000 |5,400,000 | Cubic Feet at 45 | | | | | | lbs. pressure | | | | | | at engines | | | | | | Deduction for | 17,928 | 70,927 | 154,429 | 267,529 | 409,346 | friction and | | | | | | leakage | | | | | | Estimated net | 1,062,072 | 2,089,073 |3,085,571 | 4,052,471 |4,990,654 | delivery | | | | | | -----------------------------------------------------------------------------

CAPITAL | | | | | | EXPENDITURE-- | | | | | | Purchase and pre-| £12,500 | (amounts below apply to extension of works) | paration of land | | | | | | Machinery | 27,854 | £25,595 | £25,595 | £25,595 | £25,595 | Mains | 10,328 | 10.328 | 10,328 | 10,328 | 10,328 | Buildings | 8,505 | 4,516 | 4,632 | 4,614 | 4,594 | Parlimentary and | | | | | | general expenses,| 20,000 | .. | .. | .. | .. | royalty, &c. | | | | | | Engineering | 3,268 | 1,820 | 1,825 | 1,824 | 8,823 | Previous Capit-| | 82,455 | 124,714 | 167,094 | 209,455 | al Expenditure | .. | | | | | Total Cap. Exp. | £82,455 | £124,714 | £167,094 | £209,455 | £251,795 | -----------------------------------------------------------------------------

ANNUAL CHARGES-- | | | | | | Salaries, wages, | | | | | | & general working| £6,405 | £7,855 | £9,305 | £10,955 | £12,480 | expenses | | | | | | Repairs, renewals| 2,780 | 5,198 | 7,622 | 10,045 | 12,467 | &c.(reserve fund)| | | | | | Coal, water, &c. | 1,950 | 3,900 | 5,850 | 7,800 | 9,750 | Rates | 370 | 674 | 980 | 1,285 | 1,585 | Contingencies of | | | | | | horse power = 5 | 575 | 881 | 1,187 | 1,504 | 1,814 | per cent on above| | | | | | Total Ann. Exp. | £12,080 | £18,508 | £24,944 | £31,589 | £38,096 | -----------------------------------------------------------------------------

Revenue at 5d. | | | | | | per 1000 cub. ft.| 22,126 | 43,522 | 64,282 | 84,426 | 103,971 | (average) | | | | | | Profit |12.18 p.ct.|20.06 p.ct.|23.54 p.ct.|25.22 p.ct.|26.16 p.ct.| |= 10,046 | = 25,014 | = 39,338 | = 52,837 | = 65,875 | -----------------------------------------------------------------------------

TABLE II.--_Cost of Air Power in Terms of Indicated Horse Power_.

Abbreviated column headings:

Qty. Air: Quantity of Air at 45 lbs. Pressure required per Ind. H.P. per Hour.

Cost/Hr.: Cost per Hour at 5d. per 1000 Cubic Feet.

Cost/Hr. w/rebate: Cost per Hour with Rebate when Profits reach 26 per Cent.

Cost/Yr.: Cost per Annum (2700 Hours) at 5d. per 1000 Cubic Feet.

Cost/Yr. w/rebate: Cost per Annum with Rebate when Profits reach 26 per Cent.

Abbreviated row headings:

CASE 1.--Where air at 45 lbs. pressure is re-heated to 320° Fahr., and expanded to atmospheric pressure.

CASE 2.--Where air at 45 lbs. pressure is heated by boiling water to 212° Fahr., and expanded to atmospheric pressure.

CASE 3.--Where air is used expansively without re-heating, whereby intensely cold air is exhausted, and may be used for ice making, &c.

CASE 4.--Where air is heated to 212° Fahr., and the terminal pressure is 11.3 lbs. above that of the atmosphere

CASE 5.--Where the air is used without heating, and cut off at one-third of the stroke, as in ordinary slide-valve engines

CASE 6.--Where the air is used without re-heating and without expansion.

_____________________________________________________________________ | Qty. Air | Cost/Hr. | Cost/Hr. | Cost/Yr. | Cost/Yr. | | | | w/rebate | | w/rebate | | Cub. Ft. | d. | d. | £ s. d. | £ s. d.| --------------------------------------------------------------------- CASE 1 | 125.4 | 0.627 | 0.596 | 7 1 1 | 6 14 0½| CASE 2 | 140.4 | 0.702 | 0.667 | 7 17 11 | 7 10 0 | CASE 3 | 178.2 | 0.891 | 0.847 | 10 0 5½ | 9 10 5½| CASE 4 | 170.2 | 0.851 | 0.809 | 9 11 5½ | 9 1 10½| CASE 5 | 258.0 | 1.290 | 1.226 | 14 10 3 | 13 15 9 | CASE 6 | 331.8 | 1.659 | 1.576 | 18 13 3 | 17 14 7 | _____________________________________________________________________

The great thing to guard against is leakage. If the pipes were simply buried in the ground, it would be almost impossible to trace leakage, or even to know of its existence. The income of the company might be wasting away, and the loss never suspected until the quarterly returns from the meters were obtained from the inspectors. Only then would it be discovered that there must be a great leak (or it might be several leaks) somewhere. But how would it be possible to trace them among 20 or 30 miles of buried pipes? We cannot break up the public streets. The very existence of the concern depends upon (1) the _daily_ checking of the meter returns, and comparison with the output from the air compressors, so as to ascertain the amount of leakage; (2) facility for tracing the locality of a leak; and (3) easy access to the mains with the minimum of disturbance to the streets. It will be readily understood, from the drawings, how this is effected. First, the pipes are laid in concrete troughs, near the surface of the road, with removable concrete covers strong enough to stand any overhead traffic. At intervals there are junctions for service connections, with street boxes and covers serving as inspection chambers. These chambers are also provided over the ball-valves, which serve as stop-valves in case of necessity, and are so arranged that in case of a serious breach in the portion of main between any two of them, the rush of air to the breach will blow them up to the corresponding seats and block off the broken portion of main. The air space around the pipe in the concrete trough will convey for a long distance the whistling noise of a leak; and the inspectors, by listening at the inspection openings, will thus be enabled to rapidly trace their way almost to the exact spot where there is an escape. They have then only to remove the top surface of road metal and the concrete cover in order to expose the pipe and get at the breach. Leaks would mostly be found at joints; and, by measuring from the nearest street opening, the inspectors would know where to break open the road to arrive at the probable locality of the leak. A very slight leak can be heard a long way off by its peculiar whistling sound.

The next point is to obtain a daily report of the condition of the mains and the amount of leakage. It would be impracticable to employ an army of meter inspectors to take the records daily from all the meters in the district. We therefore adopt the method of electric signaling shown in the second drawing. In the engineer's office, at the central station, is fixed the dial shown in Fig. 1. Each consumer's meter is fitted with the contact-making apparatus shown in Pig. 4, and in an enlarged form in Figs. 5 and 6, by which a current is sent round the electro-magnet, D (Fig. 1), attracting the armature, and drawing the disk forward sufficiently for the roller at I to pass over the center of one of the pins, and so drop in between that and the next pin, thus completing the motion, and holding the disk steadily opposite the figure. This action takes place on any meter completing a unit of measurement of (say) 1,000 cubic feet, at which point the contact makers touch. But suppose one meter should be moving very slowly, and so retaining contact for some time, while other meters were working rapidly; the armature at D would then be held up to the magnet by the prolonged contact maintained by the slow moving meter, and so prevent the quick working meters from actuating it; and they would therefore pass the contact points without recording. A meter might also stop dead at the point of contact on shutting off the air, and so hold up the armature; thus preventing others from acting. To obviate this, we apply the disengaging apparatus shown at L (Fig. 4). The contact maker works on the center, m, having an armature on its opposite end. On contact being made, at the same time that the magnet, D, is operated, the one at L is also operated, attracting the armature, and throwing over the end of the contact maker, l¹, on to the non-conducting side of the pin on the disk. Thus the whole movement is rendered practically instantaneous, and the magnet at D is set at liberty for the next operation. A resistance can be interposed at L, if necessary, to regulate the period of the operation. The whole of the meters work the common dial shown in Fig. 1, on which the gross results only are recorded; and this is all we want to know in this way. The action is so rapid, owing to the use of the magnetic disengaging gear, that the chances of two or more meters making contact at the same moment are rendered extremely small. Should such a thing happen, it would not matter, as it is only approximate results that we require in this case; and the error, if any, would add to the apparent amount of leakage, and so be on the right side. Of course, the record of each consumer's meter would be taken by the inspector at the end of every quarter, in order to make out the bill; and the totals thus obtained would be checked by the gross results indicated by the main dial. In this way, by a comparison of these results, a coefficient would soon be arrived at, by which the daily recorded results could be corrected to an extremely accurate measurement. At the end of the working day, the engineer has merely to take down from the dial in his office the total record of air measured to the consumers, also the output of air from the compressors, which he ascertains by means of a continuous counter on the engines, and the difference between the two will represent the loss. If the loss is trifling, he will pass it over; if serious, he will send out his inspectors to trace it. Thus there could be no long continued leakage, misuse, or robbery of the air, without the company becoming aware of the fact, and so being enabled to take measures to stop or prevent it. The foregoing are absolutely essential adjuncts to any scheme of public motive power supply by compressed air, without which we should be working in the dark, and could never be sure whether the company were losing or making money. With them, we know where we are and what we are doing.

Referring to the estimates given in Table I., I may explain that the item of repairs and renewals covers 10 per cent. on boilers and gas producers, 5 per cent. on engines, 5 per cent. on buildings, and 5 per cent. on mains. Considering that the estimates include ample fitting shops, with the best and most suitable tools, and that the wages list includes a staff of men whose chief work would be to attend to repairs, etc., I think the above allowances ample. Each item also includes 5 per cent. for contingencies.

I have commenced by giving all the preceding detail, in order to show the groundwork on which I base the estimate of the cost of compressed air power to consumers, in terms of indicated horse power per annum, as given in Table II. I may say that, in estimating the engine power and coal consumption, I have not, as in the original report, made purely theoretical calculations, but have taken diagrams from engines in actual use (although of somewhat smaller size than those intended to be employed), and have worked out the results therefrom. It will, I hope, be seen that, with all the safeguards we have provided, we may fairly reckon upon having for sale the stated quantity of air produced by means of the plant, as estimated, and at the specified annual cost; and that therefore the statement of cost per indicated horse power per annum may be fairly relied upon. Thus the cost of compressed air to the consumer, based upon an _average_ charge of 5d. per 1,000 cubic feet, will vary from £6 14s. per indicated horse power per annum to £18 13s. 3d., according to circumstances and mode of application.

A compressed air motor is an exceedingly simple machine--much simpler than an ordinary steam engine. But the air may also be used in an ordinary steam engine; and in this case it can be much simplified in many details. Very little packing is needed, as there is no nuisance from gland leakage; the friction is therefore very slight. Pistons and glands are packed with soapstone, or other self-lubricating packing; and no oil is required except for bearings, etc. The company will undertake the periodical inspection and overhauling of engines supplied with their power, all which is included in the estimates. The total cost to consumers, with air at an average of 5d. per 1,000 cubic feet, may therefore be fairly taken as follows:

Min. Max. Cost of air used £6 14 0½ £18 13 3 Oil. waste, packing, etc. 1 0 0 1 0 0 Interest, depreciation, etc., 12½ per cent. on £10, the cost of engine per indicated horse power 1 5 0 1 5 0 -------- --------- £8 19 0½ £20 18 3

The maximum case would apply only to direct acting engines, such as Tangye pumps, air power hammers, etc., where the air is full on till the end of the stroke, and where there is no expansion. The minimum given is at the average rate of 5d. per 1,000 cubic feet; but as there will be rates below this, according to a sliding scale, we may fairly take it that the lowest charge will fall considerably below £6 per indicated horse power per annum.--_Journal of Gas Lighting_.

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THE BERTHON COLLAPSIBLE CANOE.

An endeavor has often been made to construct a canoe that a person can easily carry overland and put into the water without aid, and convert into a sailboat. The system that we now call attention to is very well contrived, very light, easily taken apart, and for some years past has met with much favor.

Mr. Berthon's canoes are made of impervious oil-skin. Form is given them by two stiff wooden gunwales which are held in position by struts that can be easily put in and taken out. The model shown in the figure is covered with oiled canvas, and is provided with a double paddle and a small sail. Fig. 2 represents it collapsed and being carried overland.

Mr. Berthon is manufacturing a still simpler style, which is provided with two oars, as in an ordinary canoe. This model, which is much used in England by fishermen and hunters, has for several years past been employed in the French navy, in connection with movable defenses. At present, every torpedo boat carries one or two of these canoes, each composed of two independent halves that may be put into the water separately or be joined together by an iron rod.

These boats ride the water very well, and are very valuable for exploring quarters whither torpedo boats could not adventure without danger.[1]--_La Nature_.

[Footnote 1: For detailed description see SUPPLEMENT, No. 84.]

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THE FIFTIETH ANNIVERSARY OF THE OPENING OF THE FIRST GERMAN STEAM RAILROAD.

There was great excitement in Nürnberg on the 7th of December, 1835, on which day the first German railroad was opened. The great square on which the buildings of the Nürnberg and Furth "Ludwig's Road" stood, the neighboring streets, and, in fact, the whole road between the two cities, was filled with a crowd of people who flocked from far and near to see the wonderful spectacle. For the first time, a railroad train filled with passengers was to be drawn from Nürnberg to Furth by the invisible power of the steam horse. At eight o'clock in the morning, the civil and military authorities, etc., who took part in the celebration were assembled on the square, and the gayly decorated train started off to an accompaniment of music, cannonading, cheering, etc. Everything passed off without an accident; the work was a success. The engraving in the lower right-hand corner represents the engine and cars of this road.