STEVINUS AND THE LAW OF EQUILIBRIUM

STEVINUS AND THE LAW OF EQUILIBRIUM

It appears, then, that the mechanical studies of Galileo, taken

as a whole, were nothing less than revolutionary. They

constituted the first great advance upon the dynamic studies of

Archimedes, and then led to the secure foundation for one of t 20420d32u he

most important of modern sciences. We shall see that an important

company of students entered the field immediately after the time

of Galileo, and carried forward the work he had so well begun.

But before passing on to the consideration of their labors, we

must consider work in allied fields of two men who were

contemporaries of Galileo and whose original labors were in some

respects scarcely less important than his own. These men are the

Dutchman Stevinus, who must always be remembered as a co-laborer

with Galileo in the foundation of the science of dynamics, and

the Englishman Gilbert, to whom is due the unqualified praise of

first subjecting the phenomenon of magnetism to a strictly

scientific investigation.

Stevinus was born in the year 1548, and died in 1620. He was a

man of a practical genius, and he attracted the attention of his

non-scientific contemporaries, among other ways, by the

construction of a curious land-craft, which, mounted on wheels,

was to be propelled by sails like a boat. Not only did he write a

book on this curious horseless carriage, but he put his idea into

practical application, producing a vehicle which actually

traversed the distance between Scheveningen and Petton, with no

fewer than twenty-seven passengers, one of them being Prince

Maurice of Orange. This demonstration was made about the year

1600. It does not appear, however, that any important use was

made of the strange vehicle; but the man who invented it put his

mechanical ingenuity to other use with better effect. It was he

who solved the problem of oblique forces, and who discovered the

important hydrostatic principle that the pressure of fluids is

proportionate to their depth, without regard to the shape of the

including vessel.

The study of oblique forces was made by Stevinus with the aid of

inclined planes. His most demonstrative experiment was a very

simple one, in which a chain of balls of equal weight was hung

from a triangle; the triangle being so constructed as to rest on

a horizontal base, the oblique sides bearing the relation to each

other of two to one. Stevinus found that his chain of balls just

balanced when four balls were on the longer side and two on the

shorter and steeper side. The balancing of force thus brought

about constituted a stable equilibrium, Stevinus being the first

to discriminate between such a condition and the unbalanced

condition called unstable equilibrium. By this simple experiment

was laid the foundation of the science of statics. Stevinus had a

full grasp of the principle which his experiment involved, and he

applied it to the solution of oblique forces in all directions.

Earlier investigations of Stevinus were published in 1608. His

collected works were published at Leyden in 1634.

This study of the equilibrium of pressure of bodies at rest led

Stevinus, not unnaturally, to consider the allied subject of the

pressure of liquids. He is to be credited with the explanation of

the so-called hydrostatic paradox. The familiar modern experiment

which illustrates this paradox is made by inserting a long

perpendicular tube of small caliber into the top of a tight

barrel. On filling the barrel and tube with water, it is possible

to produce a pressure which will burst the barrel, though it be a

strong one, and though the actual weight of water in the tube is

comparatively insignificant. This illustrates the fact that the

pressure at the bottom of a column of liquid is proportionate to

the height of the column, and not to its bulk, this being the

hydrostatic paradox in question. The explanation is that an

enclosed fluid under pressure exerts an equal force upon all

parts of the circumscribing wall; the aggregate pressure may,

therefore, be increased indefinitely by increasing the surface.

It is this principle, of course, which is utilized in the

familiar hydrostatic press. Theoretical explanations of the

pressure of liquids were supplied a generation or two later by

numerous investigators, including Newton, but the practical

refoundation of the science of hydrostatics in modern times dates

from the experiments of Stevinus.