按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
he effected by enabling the owner so to alter the sliders as to
render the lock inaccessible to such key if applied by any other
person but himself； or until the sliders had been rearranged so as to
admit of its proper action。 We may mention in passing that the
security of Bramah's locks depends on the doctrine of combinations；
or multiplication of numbers into each other； which is known to
increase in the most rapid proportion。 Thus； a lock of five slides
admits of 3；000 variations； while one of eight will have no less than
1；935；360 changes； in other words； that number of attempts at making
a key； or at picking it； may be made before it can be opened。
。。。＇
and still holds its ground。 For a long time； indeed； Bramah's lock
was regarded as absolutely inviolable； and it remained unpicked for
sixty…seven years until Hobbs the American mastered it in 1851。 A
notice had long been exhibited in Bramah's shop…window in Piccadilly；
offering 200L。 to any one who should succeed in picking the patent
lock。 Many tried； and all failed； until Hobbs succeeded； after
sixteen days' manipulation of it with various elaborate instruments。
But the difficulty with which the lock was picked showed that； for
all ordinary purposes； it might be pronounced impregnable。
The new locks were machines of the most delicate kind； the action of
which depended in a great measure upon the precision with which the
springs； sliders； levers； barrels； and other parts were finished。 The
merits of the invention being generally admitted； there was a
considerable demand for the locks； and the necessity thus arose for
inventing a series of original machine…tools to enable them to be
manufactured in sufficient quantities to meet the demand。 It is
probable； indeed； that； but for the contrivance of such tools； the
lock could never have come in to general use； as the skill of
hand…workmen； no matter how experienced； could not have been relied
upon for turning out the article with that degree of accuracy and
finish in all the parts which was indispensable for its proper
action。 In conducting the manufacture throughout； Bramah was greatly
assisted by Henry Maudslay； his foreman； to whom he was in no small
degree indebted for the contrivance of those tool…machines which
enabled him to carry on the business of lock…making with advantage
and profit。
Bramah's indefatigable spirit of invention was only stimulated to
fresh efforts by the success of his lock； and in the course of a few
years we find him entering upon a more important and original line of
action than he had yet ventured on。 His patent of 1785 shows the
direction of his studies。 Watt had invented his steam…engine； which
was coming into general use； and the creation of motive…power in
various other forms became a favourite subject of inquiry with
inventors。 Bramah's first invention with this object was his
Hydrostatic Machine； founded on the doctrine of the equilibrium of
pressure in fluids； as exhibited in the well known 'hydrostatic
paradox。' In his patent of 1785； in which he no longer describes
himself as Cabinet maker； but 'Engine maker' of Piccadilly； he
indicated many inventions； though none of them came into practical
use；such as a Hydrostatical Machine and Boiler； and the application
of the power produced by them to the drawing of carriages； and the
propelling of ships by a paddle…wheel fixed in the stern of the
vessel； of which drawings are annexed to the specification； but it
was not until 1795 that he patented his Hydrostatic or Hydraulic
Press。
Though the principle on which the Hydraulic Press is founded had long
been known； and formed the subject of much curious speculation； it
remained unproductive of results until a comparatively recent period；
when the idea occurred of applying it to mechanical purposes。 A
machine of the kind was indeed proposed by Pascal； the eminent
philosopher； in 1664； but more than a century elapsed before the
difficulties in the way of its construction were satisfactorily
overcome。 Bramah's machine consists of a large and massive cylinder；
in which there works an accurately…fitted solid piston or plunger。 A
forcing…pump of very small bore communicates with the bottom of the
cylinder； and by the action of the pump…handle or lever； exceeding
small quantities of water are forced in succession beneath the piston
in the large cylinder； thus gradually raising it up； and compressing
bodies whose bulk or volume it is intended to reduce。 Hence it is
most commonly used as a packing…press； being superior to every other
contrivance of the kind that has yet been invented； and though
exercising a prodigious force； it is so easily managed that a boy can
work it。 The machine has been employed on many extraordinary
occasions in preference to other methods of applying power。 Thus
Robert Stephenson used it to hoist the gigantic tubes of the
Britannia Bridge into their bed；*
＇footnote。。。
The weight raised by a single press at the Britannia Bridge was 1144
tons。
。。。＇
and Brunel to launch the Great Eastern steamship from her cradles。 It
has also been used to cut bars of iron； to draw the piles driven in
forming coffer dams； and to wrench up trees by the roots； all of
which feats it accomplishes with comparative ease。
The principal difficulty experienced in constructing the hydraulic
press before the time of Bramah arose from the tremendous pressure
exercised by the pump； which forced the water through between the
solid piston and the side of the cylinder in which it worked in such
quantities as to render the press useless for practical purposes。
Bramah himself was at first completely baffled by this difficulty。 It
will be observed that the problem was to secure a joint sufficiently
free to let the piston slide up through it； and at the same time so
water…tight as to withstand the internal force of the pump。 These two
conditions seemed so conflicting that Bramah was almost at his wit's
end； and for a time despaired of being able to bring the machine to a
state of practical efficiency。 None but those who have occupied
themselves in the laborious and often profitless task of helping the
world to new and useful machines can have any idea of the tantalizing
anxiety which arises from the apparently petty stumbling…blocks which
for awhile impede the realization of a great idea in mechanical
invention。 Such was the case with the water…tight arrangement in the
hydraulic press。 In his early experiments； Bramah tried the expedient
of the ordinary stuffing…box for the purpose of securing the required
water tightness' That is； a coil of hemp on leather washers was
placed in a recess； so as to fit tightly round the moving ram or
piston； and it was further held in its place by means of a
compressing collar forced hard down by strong screws。 The defect of
this arrangement was； that； even supposing the packing could be made
sufficiently tight to resist the pa