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whose expansion index is practically zero for moderate changes of temperature.
If in the Julien Le Roy tube already described the steel rods were replaced by invar, the length of the brass tube B would be reduced to between 3 and 4 inches, and this length would be very manageable.
The barometric error. The period of oscillation of a pendulum may be varied without changing its effective length and without changing the arc of the swing. Thus if a pendulum with an iron bob has a magnet placed at some little distance below the bob, the clock will gain; and if the magnet be placed at some distance above the bob the clock will lose time.
In the first case the attraction of the magnet acts with gravity and increases the downward pull upon the bob and thus hastens its motion; while in the second case the magnet acts against gravity and retards the motion of the pendulum.
In like manner, when the air is heavy, that is when the barometer is high, the buoyancy of the air is relatively increased; and this buoyancy, acting against the pull of gravity, acts similarly to the magnet when placed above, and tends to retard the motion of the pendulum and to make the clock lose time. So that a well regulated clock, at a mean barometer, will lose slightly when the barometer is high, and gain slightly when the barometer is low. And this is known as the barometric error.
The barometric error is in any case a very small one, and obviously it would be avoided if we could keep the tension or weight of the atmosphere constant. This can be done by enclosing the whole clock in a practically air-tight case. If the case were absolutely air-tight the tension of the air within it would be wholly unaffected by that of the air without, and would remain constant. But as this is not possible it becomes necessary to place a barometer within the case, and to have a small exhausting air pump connected with the interior. Then by exhausting until the internal barometer marks 28 inches, say, the difference in tension between the interior air and the exterior air would not be at any time more than that due to about 3 inches of mercury, or less than 11 pounds per square inch.
And under this low difference of tension percolation of air would take place very slowly, so that a few strokes of the
pump each day would keep the interior tension nearly constant.
If, in addition to this way of correcting for barometric error, we put an electro-thermostat within the case, so as to keep the temperature constant, and placed the clock in some position, such as in an underground room, where violent changes of temperature never occurred, we would overcome, almost completely, the thermometric error.
Of course, the winding shaft would have to pass through a stuffing-box, or, what is better, the clock might be wound automatically by an electric motor situated within the case.
In the finest of modern clocks the pendulum is suspended by two equal and similar springs a short distance apart, as shown in the diagram, and this is supposed
с to give a steadier motion to the pendulum than a single spring does. But if the two springs differ
C from one another materially, this mode of suspension might become very objectionable.
In many cases, also, the bob is not supported at its bottom but at a point slightly above its centre of gravity. Under this arrangement the bob need not be considered in the compensation, as the rod, and that only, is concerned.
Rod The coarser regulation of the clock is effected by a screw thread on the pendulum
Shelf rod, so that by turning the bob, or a nut at the bottom, it may be slightly raised or lowered, according as the clock is losing or gaining. The finer and final regulation is carried
Bob out by placing small weights, as may be required, upon a shelf on the pendulum rod, the clock having been so adjusted by the coarser means as to have a slight losing rate. When all these means of correcting
Compen, errors are applied to the pendulum it becomes a perfect governor in as far as human ingenuity can make it so, and any further approach towards perfection must be looked for in the escapement. N. F. DUPUIS.
HOPE. THE HERITAGE OF THE RACE.
HE cosmogony of what may be regarded as the mytholog
ical element of our sacred books, contained in the first twelve chapters of Genesis, may not be scientifically or historically accurate. But the myths which attempt to describe the origin of man and the world he occupies differ so widely from the fables of other ancient religions in character and evident intent as to warrant a different interpretation of its meaning. Not only do those first chapters unequivocally express the monotheistic idea, but the first chapter, though far from being in strict accord with the accepted views of geologists and biologists, does describe a process of world building by an active creator, who worked, not by a single mandate, but through a systematic development of life from the simplest forms through more complex organisms, till man is reached. He, endowed with intellect and creative capacity, is said to be in the "likeness of God." This description of the methodical preparation of the earth for the maintenance of life culminating in the appearance on it of man, is truer to nature than the myths of any other religions.
But immediately man appears, with control of will and sense of right and wrong, a new force makes itself evident in the presence and power of law, and in measures for its enforcement. The most potent of these is punishment for its breach.
A code of laws and system to regulate life was imposed on created beings as a condition of their organization as social beings. The laws, however, expressed, became more intricate as man's relations became more complicated. But as long as men obey the laws, the laws work for their happiness; if they break them, the laws carry their own penalty. The ideal paradise never existed, but it is not an impossible condition. Primitive man is free from many of the vices and consequences of the diseases of civilized man; and animals, until taught to fear man, seek his companionship. If we regard law as God's will and its breach as sin, we merely give different names to unalterablef acts. The fall of man; the lawlessness of Adam's descendents, as illustrated by the feud between his sons; the recklessness of the whole race, bringing upon itself such calamities as the deluge; the growth of pride and presumption, and its punishment, as told in the story of the Tower of Babel, constitute a chain of fables with a profound ethical meaning. They enforce recognition of the reign of inexorable law,and the penalty involved in its breach. But throughout the dismal narrative of the crimes of his creatures and the vengance of the lawgiver, there is a strain of hope—the promise of salvation and protection of the race—at any rate from exinction.
Later on, as the story of the development of the race, typified in the family of Abraham, gradually merges from mythology into history, the same lesson is taught,—that the affairs of the world are controlled by a single God, who is the source of law and order, but that man, endowed with liberty to set at defiance his laws, can only do so at the peril of suffering. At first the vision of Israel was confined to this life, where facts witnessed to the reality of their creed; but gradually higher conceptions of existence and of the wider prevalence of law were conceived by Israel's prophets and seers, till in the fulness of time appeared a man, in whom men beheld the glory of the only begotten of the Father, full of Grace and Truth. By the exhibition of these virtues, even more than by a display of the knowledge of and control over the forces of nature He revealed God to man; and in His life and death He repeated the old, old story that there is relief provided for the culprit who breaks the law and exposes himself to the penalty. The theological dogma expresses the probable therapeutical fact that there is an antitoxin for every toxin which may be introduced into the human system, and that the disease often generates its own toxin. In some such sense St. Paul expresses the therapeutic idea of salvation when he says of Jesus, "He was made sin for us." This has not been proved, but it will probably be found to be the case that every disease when traced to its source, is due to and the effect of, some breach of some law of nature, inherited, acquired, or committed by ourselves. Disease is therefore the result of sin committed. But the same Providence which pronounced this judgment, has mercifully provided relief from disease and pardon for sins. The day may come, and recent advances in medicine, surgery and psychotherapy bring it almost within sight, when every disease may be controlled. But even when this consummation is reached it does not follow that the span of life will not be closed by death, but it does mean that death may become a painless step in the endless progress of our existence. It may come as when sleep wraps our senses in forgetfulness and refreshment, not through the suffering of disease and the final struggle. It would be the euthanasia of man in a sinless world. But to cure man's moral nature from its tendencies to sin will be a more difficult process than to eradicate disease.
Christ died helplessly on the Cross. Yet healing was his appropriate function. None of the prophets of Israel had claimed as their mission the rescue of man from his sins, and from disease as the result of his sins; and none, if we except Elijah and Elisha, are described as possessing the power which he exercised over sickneses and death. But may we not assume that the influence which he possessed and could render effective was some natural force which he, with his superhuman abilities, could control and bring to bear on the diseased organs of others. We all know how a strong, masterful man dominates all he comes in contact with, and what a healing power a doctor possesses who commands the full confidence of his patient and never allows him to doubt his knowledge of his case and his ability to help him. We know that in cetrain diseases despair almost inevitably means death, while confidence of recovery is the very best medicine.
Most of the recorded cases of the Master's cures were of nervous affections, such as insanity, paraylsis, or blindness. However we may interpret His mission, His personality, measured by His influence on His generation and the world for twenty centuries, was that of a being of superlative power, who could wield the forces of mind and will, inherent feebly in the ordinary man, with all the energy of God. He claimed to forgive sins, and he healed disease, the result of sin—two allied prerogatives. We may not be able to use His methods but the more we study the psychic influence over disease, both in producing and curing it, the more credible it becomes that the Master was using natural methods, though miraculous in appearance, when he caused the lame to walk, stimulated