"It is shown by ligature that there is continuous motion of the blood from arteries to veins.

"Whence ? it is demonstrated that there is a continuous motion of the blood in a circle, affected by the beat of the heart."

It was not till 1628 that Harvey published his _Anatomical Disquisition on the Motion of the Heart and Blood in Animals_. It gives the experimental basis of his conclusions. If a live snake be laid open, the heart will be seen pulsating and propelling its contents. Compress the large vein entering the heart, and the part intervening between the point of constriction and the heart becomes empty and the organ pales and shrinks. Remove the pressure, and the size and color of the heart are restored. Now compress the artery leading from the organ, and the part between the heart and the point of pressure, and the heart itself, become distended and take on a deep purple color. The course of the blood is evidently from the vena cava through the heart to the aorta.

Harvey in his investigations made use of many species of animals--at least eighty-seven.

It was believed by some, before Harvey's demonstrations, that the arteries were hollow pipes carrying air from the lungs throughout the body, although Galen had shown by cutting a dog's trachea, inflating the lungs and tying the trachea, that the lungs were in an enclosing sack which retained the air. Harvey, following Galen, held that the pulmonary artery, carrying blood to the lungs from the right side of the heart, and the pulmonary veins, carrying blood from the lungs to the left side of the heart, intercommunicate in the hidden porosities of the lungs and through minute inosculations.

In man the vena cava carries the blood to the right side of the heart, the pulmonary artery inosculates with the pulmonary veins, which convey it to the left side of the heart. This muscular pump drives it into the aorta. It still remains to be shown that in the limbs the blood pa.s.ses from the arteries to the veins. Bandage the arm so tightly that no pulse is felt at the wrist. The hand appears at first natural, and then grows cold. Loose the bandage sufficiently to restore the pulse. The hand and forearm become suffused and swollen. In the first place the supply of blood from the deep-lying arteries is cut off. In the second case the blood returning by the superficial veins is dammed back. In the limbs as in the lungs the blood pa.s.ses from artery to vein by anastomoses and porosities. All these arteries have their source in the aorta; all these veins pour their stream ultimately into the vena cava. The veins have valves, which prevent the blood flowing except toward the heart. Again, the veins and arteries form a connected system; for through either a vein or an artery all the blood may be drained off. The arguments by which Harvey supported his view were various. The opening clause of his first chapter, "When I first gave my mind to vivisection as a means of discovering the motions and uses of the heart," throws a strong light on his special method of experimental investigation.

Bacon, stimulated by what he called _philanthropia_, always aimed, as we have seen, to establish man's control over nature. But all power of a high order depends on an understanding of the essential character, or law, of heat, light, sound, gravity, and the like. Nothing short of a knowledge of the underlying nature of phenomena can give science advantage over chance in hitting upon useful discoveries and inventions.

It is, therefore, natural to find him applying his method of induction--his special method of true induction--to the investigation of heat.

In the first place, let there be mustered, without premature speculation, all the instances in which heat is manifested--flame, lightning, sun's rays, quicklime sprinkled with water, damp hay, animal heat, hot liquids, bodies subjected to friction. Add to these, instances in which heat seems to be absent, as moon's rays, sun's rays on mountains, oblique rays in the polar circle. Try the experiment of concentrating on a thermoscope, by means of a burning-gla.s.s, the moon's rays. Try with the burning-gla.s.s to concentrate heat from hot iron, from common flame, from boiling water. Try a concave gla.s.s with the sun's rays to see whether a diminution of heat results. Then make record of other instances, in which heat is found in varying degrees. For example, an anvil grows hot under the hammer. A thin plate of metal under continuous blows might grow red like ignited iron. Let this be tried as an experiment.

After the presentation of these instances induction itself must be set to work to find out what factor is ever present in the positive instances, what factor is ever wanting in the negative instances, what factor always varies in the instances which show variation. According to Bacon it is in the process of exclusion that the foundations of true induction are laid. We can be certain, for example, that the essential nature of heat does not consist in light and brightness, since it is present in boiling water and absent in the moon's rays.

The induction, however, is not complete till something positive is established. At this point in the investigation it is permissible to venture an hypothesis in reference to the essential character of heat.

From a survey of the instances, all and each, it appears that the nature of which heat is a particular case is motion. This is suggested by flame, simmering liquids, the excitement of heat by motion, the extinction of fire by compression, etc. Motion is the genus of which heat is the species. Heat itself, its essence, is motion and nothing else.

It remains to establish its specific differences. This accomplished, we arrive at the definition: Heat is a motion, expansive, restrained, and acting in its strife upon the smaller particles of bodies. Bacon, glancing toward the application of this discovery, adds: "_If in any natural body you can excite a dilating or expanding motion, and can so repress this motion and turn it back upon itself, that the dilation shall not proceed equally, but have its way in one part and be counteracted in another, you will undoubtedly generate heat._" The reader will recall that Bacon looked for the invention of instruments that would generate heat solely by motion.

Descartes was a philosopher and mathematician. In his _Discourse on Method_ and his _Rules for the Direction of the Mind_ (1628) he laid emphasis on deduction rather than on induction. In the subordination of particulars to general principles he experienced a satisfaction akin to the sense of beauty or the joy of artistic production. He speaks enthusiastically of that pleasure which one feels in truth, and which in this world is about the only pure and unmixed happiness.

At the same time he shared Bacon's distrust of the Aristotelian logic and maintained that ordinary dialectic is valueless for those who desire to investigate the truth of things. There is need of a method for finding out the truth. He compares himself to a smith forced to begin at the beginning by fashioning tools with which to work.

In his method of discovery he determined to accept nothing as true that he did not clearly recognize to be so. He stood against a.s.sumptions, and insisted on rigid proof. Trust only what is completely known. Attain a cert.i.tude equal to that of arithmetic and geometry. This att.i.tude of strict criticism is characteristic of the scientific mind.

Again, Descartes was bent on a.n.a.lyzing each difficulty in order to solve it; to neglect no intermediate steps in the deduction, but to make the enumeration of details adequate and methodical. Preserve a certain order; do not attempt to jump from the ground to the gable, but rise gradually from what is simple and easily understood.

Descartes' interest was not in the several branches of mathematics; rather he wished to establish a universal mathematics, a general science relating to order and measurement. He considered all physical nature, including the human body, as a mechanism, capable of explanation on mathematical principles. But his immediate interest lay in numerical relationships and geometrical proportions.

Recognizing that the understanding was dependent on the other powers of the mind, Descartes resorted in his mathematical demonstrations to the use of lines, because he could find no method, as he says, more simple or more capable of appealing to the imagination and senses. He considered, however, that in order to bear the relationships in memory or to embrace several at once, it was essential to explain them by certain formulae, the shorter the better. And for this purpose it was requisite to borrow all that was best in geometrical a.n.a.lysis and algebra, and to correct the errors of one by the other.

Descartes was above all a mathematician, and as such he may be regarded as a forerunner of Newton and other scientists; at the same time he developed an exact scientific method, which he believed applicable to all departments of human thought. "Those long chains of reasoning," he says, "quite simple and easy, which geometers are wont to employ in the accomplishment of their most difficult demonstrations, led me to think that everything which might fall under the cognizance of the human mind might be connected together in the same manner, and that, provided only one should take care not to receive anything as true which was not so, and if one were always careful to preserve the order necessary for deducing one truth from another, there would be none so remote at which he might not at last arrive, or so concealed which he might not discover."

REFERENCES

Francis Bacon, _Philosophical Works_ (Ellis and Spedding edition), vol.

IV, Novum Organum.

J. J. Fahie, _Galileo; His Life and Work_.

Galileo, _Two New Sciences_; translated by Henry Crew and Alphonse De Salvio.

William Gilbert, _On the Loadstone_; translated by P. F. Mottelay.

William Harvey, _An Anatomical Disquisition on the Motion of the Heart and Blood in Animals_.

T. H. Huxley, _Method and Results_.

D'Arcy Power, _William Harvey_ (in _Masters of Medicine_).

FOOTNOTES:

[1] This is Harvey's monogram, which he used in his notes to mark any original observation.

CHAPTER VII

SCIENCE AS MEASUREMENT--TYCHO BRAHE, KEPLER, BOYLE

Considering the value for clearness of thought of counting, measuring and weighing, it is not surprising to find that in the seventeenth century, and even at the end of the sixteenth, the advance of the sciences was accompanied by increased exactness of measurement and by the invention of instruments of precision. The improvement of the simple microscope, the invention of the compound microscope, of the telescope, the micrometer, the barometer, the thermoscope, the thermometer, the pendulum clock, the improvement of the mural quadrant, s.e.xtant, spheres, astrolabes, belong to this period.

Measuring is a sort of counting, and weighing a form of measuring. We may count disparate things whether like or unlike. When we measure or weigh we apply a standard and count the times that the unit--cubit, pound, hour--is found to repeat itself. We apply our measure to uniform extension, meting out the waters by fathoms or s.p.a.ce by the sun's diameter, and even subject time to arbitrary divisions. The human mind has been developed through contact with the multiplicity of physical objects, and we find it impossible to think clearly and scientifically about our environment without dividing, weighing, measuring, counting.

In measuring time we cannot rely on our inward impressions; we even criticize these impressions and speak of time as going slowly or quickly. We are compelled in the interests of accuracy to provide an objective standard in the clock, or the revolving earth, or some other measurable thing. Similarly with weight and heat; we cannot rely on the subjective impression, but must devise apparatus to record by a measurable movement the amount of the pressure or the degree of temperature.

"G.o.d ordered all things by measure, number, and weight." The scientific mind does not rest satisfied till it is able to see phenomena in their number relationships. Scientific thought is in this sense Pythagorean, that it inquires in reference to quant.i.ty and proportion.

As implied in a previous chapter, number relations are not clearly grasped by primitive races. Many primitive languages have no words for numerals higher than five. That fact does not imply that these races do not know the difference between large and small numbers, but precision grows with civilization, with commercial pursuits, and other activities, such as the practice of medicine, to which the use of weights and measures is essential. Scientific accuracy is dependent on words and other means of numerical expression. From the use of fingers and toes, a rude score or tally, knots on a string, or a simple abacus, the race advances to greater refinement of numerical expression and the employment of more and more accurate apparatus.

One of the greatest contributors to this advance was the celebrated Danish astronomer, Tycho Brahe (1546-1601). Before 1597 he had completed his great mural quadrant at the observatory of Uraniborg. He called it with characteristic vanity the Tichonic quadrant. It consisted of a graduated arc of solid polished bra.s.s five inches broad, two inches thick, and with a radius of about six and three quarters feet. Each degree was divided into minutes, and each minute into six parts. Each of these parts was then subdivided into ten seconds, which were indicated by dots arranged in transverse oblique lines on the width of bra.s.s.

[Ill.u.s.tration: THE TICHONIC QUADRANT]

The arc was attached in the observation room to a wall running exactly north, and so secured with screws (_firmissimis cochleis_) that no force could move it. With its concavity toward the southern sky it was closely comparable, though reverse, to the celestial meridian throughout its length from horizon to zenith. The south wall, above the point where the radii of the quadrant met, was pierced by a cylinder of gilded bra.s.s placed in a rectangular opening, which could be opened or closed from the outside. The observation was made through one of two sights that were attached to the graduated arc and could be moved from point to point on it. In the sights were parallel slits, right, left, upper, lower. If the alt.i.tude and the transit through the meridian were to be taken at the same time the four directions were to be followed. It was the practice for the student making the observation to read off the number of degrees, minutes, etc., of the angle at which the alt.i.tude or transit was observed, so that it might be recorded by a second student.

A third took the time from two clock dials when the observer gave the signal, and the exact moment of observation was also recorded by student number two. The clocks recorded minutes and the smaller divisions of time; great care, however, was required to obtain good results from them. There were four clocks in the observatory, of which the largest had three wheels, one wheel of pure solid bra.s.s having twelve hundred teeth and a diameter of two cubits.

Lest any s.p.a.ce on the wall should lie empty a number of paintings were added: Tycho himself in an easy att.i.tude seated at a table and directing from a book the work of his students. Over his head is an automatic celestial globe invented by Tycho and constructed at his own expense in 1590. Over the globe is a part of Tycho's library. On either side are represented as hanging small pictures of Tycho's patron, Frederick II of Denmark (d. 1588) and Queen Sophia. Then other instruments and rooms of the observatory are pictured; Tycho's students, of whom there were always at least six or eight, not to mention younger pupils. There appears also his great bra.s.s globe six feet in diameter. Then there is pictured Tycho's chemical laboratory, on which he has expended much money. Finally comes one of Tycho's hunting dogs--very faithful and sagacious; he serves here as a hieroglyph of his master's n.o.bility as well as of sagacity and fidelity. The expert architect and the two artists who a.s.sisted Tycho are delineated in the landscape and even in the setting sun in the top-most part of the painting, and in the decoration above.

The princ.i.p.al use of this largest quadrant was the determination of the angle of elevation of the stars within the sixth part of a minute, the collineation being made by means of one of the sights, the parallel horizontal slits in which were aligned with the corresponding parts of the circ.u.mference of the cylinder. The alt.i.tude was recorded according to the position of the sight attached to the graduated arc.

Tycho Brahe had a great reverence for Copernicus, but he did not accept his planetary system; and he felt that advance in astronomy depended on painstaking observation. For over twenty years under the kings of Denmark he had good opportunities for pursuing his investigation. The island of Hven became his property. A thoroughly equipped observatory was provided, including printing-press and workshops for the construction of apparatus. As already implied, capable a.s.sistants were at the astronomer's command. In 1598, after having left Denmark, Tycho in a splendid ill.u.s.trated book (_Astronomiae Instauratae Mechanica_) gave an account of this astronomical paradise on the Insula Venusia as he at times called it. The book, prepared for the hands of princes, contains about twenty full-page colored ill.u.s.trations of astronomical instruments (including, of course, the mural quadrant), of the exterior of the observatory of Uraniborg, etc. The author had a consciousness of his own worth, and deserves the name Tycho the Magnificent. The results that he obtained were not unworthy of the apparatus employed in his observations, and before he died at Prague in 1601, Tycho Brahe had consigned to the worthiest hands the painstaking record of his labors.

Johann Kepler (1571-1630) had been called, as the astronomer's a.s.sistant, to the Bohemian capital in 1600 and in a few months fell heir to Tycho's data in reference to 777 stars, which he made the basis of the Rudolphine tables of 1627. Kepler's genius was complementary to that of his predecessor. He was gifted with an imagination to turn observations to account. His astronomy did not rest in mere description, but sought the physical explanation. He had the artist's feeling for the beauty and harmony, which he divined before he demonstrated, in the number relations of the planetary movements. After special studies of Mars based on Tycho's data, he set forth in 1609 (_Astronomia Nova_) (1) that every planet moves in an ellipse of which the sun occupies one focus, and (2) that the area swept by the radius vector from the planet to the sun is proportional to the time. Luckily for the success of his investigation the planet on which he had concentrated his attention is the one of all the planets then known, the orbit of which most widely differs from a circle. In a later work (_Harmonica Mundi_, 1619) the t.i.tle of which, the _Harmonics of the Universe_, proclaimed his inclination to Pythagorean views, he demonstrated (3) that the square of the periodic time of any planet is proportional to the cube of its mean distance from the sun.

Kepler's studies were facilitated by the invention, in 1614 by John Napier, of logarithms, which have been said, by abridging tedious calculations, to double the life of an astronomer. About the same time Kepler in purchasing some wine was struck by the rough-and-ready method used by the merchant to determine the capacity of the wine-vessels. He applied himself for a few days to the problems of mensuration involved, and in 1615 published his treatise (_Stereometria Doliorum_) on the cubical contents of casks (or wine-jars), a source of inspiration to all later writers on the accurate determination of the volume of solids. He helped other scientists and was himself richly helped. As early as 1610 there had been presented to him a means of precision of the first importance to the progress of astronomy, namely, a Galilean telescope.

The early history of telescopes shows that the effect of combining two lenses was understood by scientists long before any particular use was made of this knowledge; and that those who are accredited with introducing perspective gla.s.ses to the public hit by accident upon the invention. Priority was claimed by two firms of spectacle-makers in Middelburg, Holland, namely, Zacharias, miscalled Jansen, and Lippershey. Galileo heard of the contrivance in July, 1609, and soon furnished so powerful an instrument of discovery that things seen through it appeared more than thirty times nearer and almost a thousand times larger than when seen by the naked eye. He was able to make out the mountains in the moon, the satellites of Jupiter in rotation, the spots on the revolving sun; but his telescope afforded only an imperfect view of Saturn. Of course these facts, published in 1610 (_Sidereus Nuncius_), strengthened his advocacy of the Copernican system. Galileo laughingly wrote Kepler that the professors of philosophy were afraid to look through his telescope lest they should fall into heresy. The German astronomer, who had years before written on the optics of astronomy, now (1611) produced his _Dioptrice_, the first satisfactory statement of the theory of the telescope.

About 1639 Gascoigne, a young Englishman, invented the micrometer, which enables an observer to adjust a telescope with very great precision.

Before the invention of the micrometer exact.i.tude was impossible, because the adjustment of the instrument depended on the discrimination of the naked eye. The micrometer was a further advance in exact measurement. Gascoigne's determinations of, for example, the diameter of the sun, bear comparison with the findings of even recent astronomical science.