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Steel for Columns. From the Lo~lou Builder, No. 1211,

In France a few experiments were made some time ago by M.*G. It. Love upon small pillars made of Turton's steel, and having rounded ends. These pillars were 1 centimetre, or 0"39 inch, in diameter, the lengths being ten, twenty, and thir.ty times the diameter. The steel of which the pillars were composed was found by experiment to have a ten- sile breaking strength of 108,500 lbs. per square inch. According to _Engineering, the results show that, as in the case of cast and wrought iron, the resisting power of steel to compression decreases as the propor- tion which the length of the column bears to the diameter is increased ; t)ut this decrease in strength does not seem to be so rapid as in the case of the two first-mentioned materials. M. Love's own deductions are, that steel and cast iron columns, having a length of from one and a l~tlf to five diameters, offer about the same resistance to compression ; whilst columns of wrought iron of the same proportions offer only about tialf such resistance. When the length of the column is increased to ~en diameters, however, he considers that steel offers a greater resist- ~lnce than cast iron, in the proportion of 41 to 3l, the proportionate resistance of wrought iron being represented by 17. As the proportion (~f length to diameter increases, the resisting power of cast iron di- Ininishes more rapidly than that of wrought iron, and that of wrought iron more quickly than that of steel, so that when the length reaches forty diameters, he estimates the strength of similar columns of the three materials to be in the proportion of the numbers 375, 562, and 1500. It is wrong to found a law upon so few experiments; but, if the dgta above given are confirmed by future trials, steel will prove a ~'~Lluable material for resisting compressive strains.

Water-19roofing Walls. By FREDERI~CK ROGERS, Captain R. N. From the London Builder, No. 1212.

Observing in the Builder a notice respecting damp walls in oat- buildings, allow me to suggest a probable cure.

While in Dorset, I was applied to by a lady for a remedy for the above, and as I had far many years been in the habit of applying "bright American varnish" with great success to very exposed wood- work, I recommended the lady to make an experiment on the part of her house where not much seen. On passing by a few weeks after- wards, I observed all the front glowing to an evening sky.

On inquiry, I found that the varnish had so well succeeded in a small way that the lady had applied the same to the whole building, with equal success ; and, when afterwards painted, there was no ap- pearance of wet or "varnish."

The "bright American varnish" is very inexpensive, costing, I think, about 3s. per gallvn, and may be procured from most sea-ports. I should recommend one coat of varnish as a trial, and if not quite successful then another, followed by three good coats of paint.

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9O

On Un~(orm Rotation. By C. W. SIEM~nS, F. R. S. From the London Artizan~ June, 1866.

The paper sets out with an inquiry into the conditions of the conical pendulum as a means of obtaining uniform rotation. This instrument, as applied by Watt to regulate the velocity of his steam engines, is shown to be defective, first, becauae the regulated position of the valve depends upon the angular position of the pendulums, and, therefore, upon the velocity of rotation, which must be permanently changed in order to effect an adjustment of the valve ; and, secondly, because when the balance between force and resistance of the engine at a given ve- locity is disturbed, the angular position of the pendulums will not change until a power has been created in them, through acceleration of the engine sufficient to overcome the mechanical resistance of the valve, giving rise to a series of fluctuations before a balance between the power and resistance of the engine is re-established.

These defects in Watt's centrifugal governor are shown to be obvi- ated in the ehronometric governor, an instrument which Was proposed by the author of the paper twenty-three years ago, and which consists of a conical pendulum proceeding at a uniform angle of rotation, and, therefore, at a uniform speed, which is made to act upon the regulat- ing valve by means of a differential motion between itself and the en- gine to be regulated, which latter has to accommodate itself to the rotations imposed by the independent pendulum. The differential mo- tion wheels are taken advantage of for imparting independent driving or sustaining power to the pendulum ; and a constancy of the angle of rotation, notwithstanding unavoidable fluctuations in the sustaining power, is secured (within certain limits) by calling into play a brake, or fluid resistance, at the moment when the angle of rotation reaches a maximum, which maximum position is perpetuated by increasing the sustaining power beyond what is strictly necessary to overcome the ordinary resistance of the pendulum.

The chronometric governor is used by the Astronomer Royal to regulate the motion of the large equatorial telescope and recording apparatus at Greenwich, in which application a very high degree of regularity is attained ; but the instrument proved to be too delicate m its adjustments for ordinary steam engine use.

After a short allusion to M. Foucoult's governor, the paper enters upon the description of a new apparatus which the writer has imagined for obtaining uniform rotation, notwithstanding great variations in the driving power, and which consists in the main of a parabolic cup, open at top and bottom and mounted upon a vertical axis, which cup dips, with its smaller opening, into a liquid contained within a easing completely enclosing the cup. ]~t is shown that a certain angular ve- locity of the cup will raise the liquid (entering from below) in a para- bolic curve to its upper edge or brim, and that a very slight increase of the velocity will cause actual overflow, in the form of a sheet of liquid, which, being raised and projected against the sides of the outer chamber, descends to the bath below, whence fresh liquid continually enters the cup. Without the overflow scarcely any power is recluired

On Uniform Rotation. 91

to maintain the cup, with the liquid it contains, in motion ; but the moment an overflow ensues, a considerable amount of power is absorbed in raising and projecting a continuous stream of the liquid whereby further acceleration is prevented, and nearly uniform velocity is the result. When absolute uniformity is required, the cup is not fixed upon the rotating axis, but is suspended from it by a spiral spring, which not only supports its weight, but also transmits the driving power by its torsional moment. The cup is guided in the centre upon a helical surface, which arrangement has ibr its result that an increase of resistance or of driving power produces an increased torsional action of the spring, and with it an automatic descent of the cup, sufficient to make up for the thickness of overflow required to effect the re-ad- justment between power and resistanoe~ without permanent increase of angular velocity.

It is shown that the density of the liquid exercises no influence upon the velocity of the cup, which velocity is expressed by the fol- lowing formula :

) ~2gh ( 1 + r2 - '293,02

2r7: in which

n signifies the number of revolutions per second, h the height of liquid from the surface to the brim of cup, r the radius of the brim, and p the radius of lower orifice of cup,

only the rigidity of the spring must be greater when a comparatively dense liquid is employed.

Ill order, to test the principle of action here involved, Mr. Siemens has constructed a clock consisting of a galvanic battery, an electro- magnet, and his gyrometric cup, besides the necessary reducing wheels and hands upon a dial face, which proceeds at a uniform rate, although the driving power may be varied between wide limits, by the intro- duction of artificial resistances into the electrical circuit. The instru- ment appears, therefore, well calculated for regulating the speed of all kinds of philosophical apparatus, and also for obtaining synchron- ous rotations at different places for telegraphic purposes. One of its most interesting applications is embodied in the "gyrometric gov- ernor" for steam engines. This consists of a cup of 200 millimetres diameter and the same height, which is fixed upon its vertical axis of rotation, and is enclosed in an outer chamber, containing water in such quantity that the lower extremity of the cup dips below its sur- face. The upper edge of the rotating cup is, in this applieation~ sur- rounded by a stationary ring armed with vertical vanes~ by which the overflowing liquid is arrested and directed downward~ causing it to fall through a space or zone which is traversed by a number of radial and vertical blades projecting from the external surface of the rotating cup, which~ in striking the tailing liquid~ project it with considerable

9~ Civil and Mechanical .Engineering.

force against the sides of the outer vessel, at the expense of a corres- ponding retarding effect ou the cup, increasing its regulating power.

The cup-spindle carries at its lower extremity a pinion, which gears into two planet-wheels at opposite points, which on their part gear into an inverted wheel surrounding the whole, which latter is fas- tened upon a vertical shaft in continuation of tile cup-spindle, and is driven round by the engine in the opposite direction to the motion of the cup. The two intermediate or planet-wheels are attached to a rocking frame supported, but not fixed, upon the central axis, which wheels, in rotating upon their studs, are also free to follow the impulse of either the pinion or the inverted wheel to the extent of the differ. ential motion arising between them. The rocking frameis connected to the regulating valve of the engine, and also to the weight suspended from a horizontal arm upon the valve-spindle, tending to open the valve and, at the same time, to accelerate the cup to the extent of the pressure produced between the teeth of the planet-wheels and tile pinion, while the engine is constantly employed to raise the weight and cut off the supply of steam. The result is that the engine has to conform ~bsolutely to the regular motion imposed by the cup, which will be precisely the same when the engine is charged with its maxi- mum or its minimum of resisting load.

The p:~per shows that the action upon the valve must take place at the moment when the balance between the power and load of the en- gine is disturbed, and that the readjustment will be effected, notwith- standing a resistance of the valve exceeding 100 kilogrammes~a re. 8ult tending towards the attainment of several important objects.

Messrs. Phillips' Patent Girders. From the London Builder, No. 1204.

:For some time past several interesting experiments on rolled iron beams of peculiar construction, have been progressing at Mr. Kirk- aldy's works, Southwark, of which our renders may desire to have some particulars. Mr. Kirkaldy's machine (a patent,) we may say at starting, is a beautiful work, from the foundry of Greenwood & Barley, of Leeds.

Several years have elapsed since the continental architects and builders began the adoption of rolled iron beams in place of the ordi- nary wooden girders and joists, and found advantages in the substitu- tion, not only in respect of cost, but also in the facility they obtained for working out conceptions which never could have had an actual ex- istence under the old mode of construction.

Now, why have we not more generally adopted the use of so con. venient a material as rolled iron .9 Years ago we suggested to the government the offering of a large premium for improvements in the mode of rolling iron. The fact is, that, with our practical habit of re- garding things, the builder is popularly believed to be the best judge