« הקודםהמשך »
the third person, masculine gender, singular num-
2dinorder, 3d' in order,
James and George and
Geo ge's By appropriating these words to their proper uses, the foregoing card would run thus,
John presents his compliments to fames, begs that
HEI will be so kind as to call upon George, and bring
John 3 pect Hom with some impatience, as he will be always George
John 3 proud to show HOM, every civility in his power, not only George
John 3 on ho's own account, from the personal regard he bears George's
3 HOM, but also on actount of ho's father, who was hi’s. George
John's. “ much respected friend.
3 4 If hei will also desire HoM to come with an intention James
“ to spend the evening with him it will give him an ad.
“ ditional pleasure ; and in that case he will endeavour to
The above card appears to read a little unconthly to us at present, because the words are new to us ; but there cannot be a doubt, that if these, or other words of the same import, were in use in language, their sounds would become familiar to the ear, and their meaning would be distinctly recognised at the first, as the words he and her are at present, or any other words in the language, and would be the source of much perspicuity and elegance.
To be continued.
AN ESSAY ON WATER,
CONSIDERED AS A MOVING POWER ACTING UPON MACHINERY.
1:0 In this essay it is not intended to engage in deep mathematical discussions, but merely to give some general notions concerning the most effectual way of applying water to machinery, in different circum. stances, that as little as possible of its effect, as a moving power, may be lost ;- an investigation pe. culiarly proper at the present time, when machinery is beginning to be universally employed in manufactures ; especially as it will be found that a great part of the effect of that useful element, as a moving
power, is now lost, from an inattention to obvious. principles in the construction of machinery.
There are two cases which may be considered as. the extremes in the application of water to turn machinery, viz. where the height of the fall that can be commanded, is very great; or where the water moves nearly on a level bottom, without admitting of a cascade or fall. If the means of applying water to machinery, in these two circumstances, so as to derive the greatest benefit possible from its power, be distinctly specified, it will be very easy to apply the principles that will thus be developed, to any intermediate cases that may occur.
Water, as a moving power, may be made to act upon machinery, either by its dead weight, or by its , impetus.
When we speak of water acting by its dead weight upon a wheel, it is meant to say, that it is so applied as to produce an effect similar to that of a man pulling a rope wound round the circumference of that wheel, moveable upon its center; or that of any other kind of weight suspended from the same rope.
When it acts by its - impetus, we mean the same thing as if a stone were thrown, so as to strike, with force, a board fixed to the edge of a wheel, moveable upon its center.
Such a stroke would make the board move ; and by a repetition of these strokes, a continued rotatory motion may be produced.
Most of the water mills in Britain are so constructed as that water acts upon them in both these ways united; but wherever the fall is considerable,
the general notion seems to prevail, that the greatest reliance ought to be placed on its power when acting by its impetus, and the effects that might result from its power as a dead weight are disregarded.
By an accurate set of experiments, conducted with great care by Mr Smeaton, the ingenious mechanician, and recorded in the Philosophical Transactions many years ago, this notion has been proved to be ill founded ; for he has demonstrated in the most sa. tisfactory manner, that, in all cases, the same quantity of water will produce a much greater effect with the same height of fall, if made to act by its dead weight than by its impetus.
The difference of power when applied in these two ways, is always great; but in some cases it is nearly infinite. Where the stream of water, for example, is small, and the height very great, the power of that water, if properly applied, by its dead weight, may be sufficient to overcome a greater resistance than any machinery could bear; while, by its impetus, it could be nothing ; the whole body of water in that way being broken by the air, and dissipated.
In a wheel constructed upon the common principles adopted in this country, with float boards, or A A's, fixed on the circumference of the wheel, a great part of the impetus is lost by the motion of the wheel ; so that, on this account, the slower the wheel is made to move,
the greater will the effect of the water be
it. A great part of the power of the water acting by its dead weight is, in this case also, lost hy the water
being thrown from the A A's, in consequence of their inclined position, where lower than the axle, upon the edges of the trough in which the wheel moves : for as there must always be a vacant space between the edge of the A A's and that trough, as much water as fills that space, must, in all cases, escape, without acting upon the wheel at all by its dead weight.
The quantity of water that thus is entirely lost will always be in proportion to the distance between the trough and the wheel. It is therefore of the utmost consequence, if we wish to lose little power, that the the trough be formed with the nicest accuracy, and be made to apply as close to the wheel as can be done, so as not to touch it.
The loss that is thus incurred will be greatest, where the velocity of the water is greatest, for a reason that shall be soon explained; therefore that loss will be always in proportion to the height of the fall, other circumstances being equal.
An opinion at present very generally prevails in this country, that a great deal of power is in all cases gained by encreasing the breadth (I do not mean the diameter) of the wheel. In other words, by making the A A's of greater length than formerly. This Opinion, however, is extremely erroneous; for where ever the fall is considerable, a dimunition of power must be the result of this alteration; and where the wheel is construkted with plain A A's, this loss, where the fall is great, may be prodigious.
To explain this circumstance, it is only necessary to remark, that the depth of a stream which transmits the same quantity of water in a given time, its breadth continuing the same, diminishes in propor