The 100 Most Influential Scientists of All Time (10 page)

After Galileo built a telescope in 1609 and announced hitherto-unknown objects in the heavens (e.g., moons revolving around Jupiter) and imperfections of the lunar surface, he sent Kepler his account in
Siderius Nuncius
(1610;
The Sidereal Messenger
). Kepler responded with three important treatises. The first was his
Dissertatio cum Nuncio Sidereo
(1610; “Conversation with the Sidereal Messenger”), in which, among other things, he speculated that the distances of the newly discovered Jovian moons might agree with the ratios of the rhombic dodecahedron, triacontahedron, and cube. The second was a theoretical work on the optics of the telescope,
Dioptrice
(1611; “Dioptrics”), including a description of a new type of telescope using two convex lenses. The third was based upon his own observations of Jupiter, made between August 30 and September 9, 1610, and published as
Narratio de Jovis Satellitibus
(1611; “Narration Concerning the Jovian Satellites”). These works provided strong support for Galileo's discoveries.

Kepler also published the first textbook of Copernican astronomy,
Epitome Astronomiae Copernicanae
(1618–21;
Epitome of Copernican Astronomy
), which proved to be the most important theoretical resource for the Copernicans in the 17th century. Galileo and French mathematician and philosopher René Descartes were probably influenced by it.

(b. April 1, 1578, Folkestone, Kent, Eng.—d. June 3, 1657, London)

E
nglish physician William Harvey was the first to recognize the full circulation of the blood in the human body and to provide experiments and arguments to support this idea.

Harvey's key work was
Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (Anatomical Exercise on the
Motion of the Heart and Blood in Animals
), published in 1628. Harvey's greatest achievement was to recognize that the blood flows rapidly around the human body, being pumped through a single system of arteries and veins, and to support this hypothesis with experiments and arguments.

Prior to Harvey, it was believed there were two separate blood systems in the body. One carried purple, “nutritive” blood and used the veins to distribute nutrition from the liver to the rest of the body. The other carried scarlet, “vivyfying” (or “vital”) blood and used the arteries to distribute a life-giving principle from the lungs. Today these blood systems are understood as deoxygenated blood and oxygenated blood. However, at the time, the influence of oxygen on blood was not understood. Furthermore, blood was not thought to circulate around the body—it was believed to be consumed by the body at the same rate that it was produced. The capillaries, small vessels linking the arteries and veins, were unknown at the time, and their existence was not confirmed until later in the 17th century, after Harvey, when the microscope had been invented.

Harvey claimed he was led to his discovery of the circulation by consideration of the venous valves. It was known that there were small flaps inside the veins that allowed free passage of blood in one direction but strongly inhibited the flow of blood in the opposite direction. It was thought that these flaps prevented pooling of the blood under the influence of gravity, but Harvey was able to show that all these flaps are cardiocentrically oriented. For example, he showed that in the jugular vein of the neck they face downward, inhibiting blood flow away from the heart, instead of upward, inhibiting pooling due to gravity.

Harvey's main experiment concerned the amount of blood flowing through the heart. He made estimates of
the volume of the ventricles, how efficient they were in expelling blood, and the number of beats per minute made by the heart. He was able to show, even with conservative estimates, that more blood passed through the heart than could possibly be accounted for based on the then current understanding of blood flow. Harvey's values indicated the heart pumped 0.5–1 litre of blood per minute (modern values are about 4 litres per minute at rest and 25 litres per minute during exercise). The human body contains about 5 litres of blood. The body simply could not produce or consume that amount of blood so rapidly; therefore, the blood had to circulate.

It is also important that Harvey investigated the nature of the heartbeat. Prior to Harvey, it was thought that the active phase of the heartbeat, when the muscles contract, was when the heart increased its internal volume. So the active motion of the heart was to draw blood into itself. Harvey observed the heart beating in many animals—particularly in cold-blooded animals and in animals near death, because their heartbeats were slow. He concluded that the active phase of the heartbeat, when the muscles contract, is when the heart decreases its internal volume and that blood is expelled with considerable force from the heart. Although Harvey did quantify blood flow, his quantification is very approximate, and he deliberately used underestimates to further his case. This is very different from the precise quantification leading to the mathematical laws of someone like Galileo.

Harvey's theory of circulation was opposed by conservative physicians, but it was well established by the time of his death. It is likely that Harvey actually made his discovery of the circulation about 1618–19. Such a major shift in thinking about the body needed to be very well supported by experiment and argument to avoid immediate ridicule and dismissal; hence the delay before the publication of his central work. In 1649 Harvey published
Exercitationes Duae Anatomicae de Circulatione Sanguinis, ad Joannem Riolanem, Filium, Parisiensem
(
Two Anatomical Exercises on the Circulation of the Blood
) in response to criticism of the circulation theory by French anatomist Jean Riolan.

Harvey was very much influenced by the ideas of Greek philosopher Aristotle and the natural magic tradition of
the Renaissance. His key analogy for the circulation of the blood was a macrocosm/microcosm analogy with the weather system. A macrocosm/microcosm analogy sees similarities between a small system and a large system. Thus, one might say that the solar system is a macrocosm and the atom is a microcosm. The Renaissance natural magic tradition was very keen on the idea of the human body as a microcosm. The macrocosm for Harvey was the Earth's weather cycle. Water was changed into vapour by the action of the Sun, and the vapour rose, was cooled, and fell again as rain. The microcosm was the human body, where the action of the heart was supposed to heat and change the blood, which was cooled again in the extremities of the body. It also should be noted that much of his terminology for change was drawn from the alchemy of his time. Harvey was very much a man of the later Renaissance—not a man of the scientific revolution and its mechanical nature.

Harvey spent much of the latter part of his career working on the nature of reproduction in animals. He worked on chickens as an example of oviparous reproduction, in which embryonic development occurs within eggs hatched outside the mother's body, and on deer as an example of viviparous reproduction, in which embryonic development occurs within the mother's body, resulting in the birth of live young. Harvey's work in this area generated a wealth of observational detail. At the time, reproduction was poorly understood, and Harvey investigated issues of the role of sperm and menstrual blood in the formation of the embryo. His observations were excellent, but such matters could not be resolved properly without the use of the microscope.

(b. Jan. 25, 1627, Lismore Castle, County Waterford, Ire.—d. Dec. 31, 1691, London, Eng.)

B
ritish natural philosopher and theological writer Robert Boyle was a preeminent figure of 17th-century intellectual culture. He was best known as a natural philosopher, particularly in the field of chemistry, but his scientific work covered many areas including hydrostatics, physics, medicine, earth sciences, natural history, and alchemy. His prolific output also included Christian devotional and ethical essays and theological tracts on biblical language, the limits of reason, and the role of the natural philosopher as a Christian. He sponsored many religious missions as well as the translation of the Scriptures into several languages. In 1660 he helped found the Royal Society of London.

Boyle spent much of 1652–54 in Ireland overseeing his hereditary lands, and he also performed some anatomic dissections. In 1654 he was invited to Oxford, and he took up residence at the university from
c
. 1656 until 1668. In Oxford he was exposed to the latest developments in natural philosophy and became associated with a group of notable natural philosophers and physicians, including John Wilkins, Christopher Wren, and John Locke. These individuals, together with a few others, formed the “Experimental Philosophy Club,” which at times convened in Boyle's lodgings. Much of Boyle's best-known work dates from this period.

In 1659 Boyle and Robert Hooke, the clever inventor and subsequent curator of experiments for the Royal Society, completed the construction of their famous air pump and used it to study pneumatics. Their resultant discoveries regarding air pressure and the vacuum appeared in Boyle's first scientific publication,
New Experiments Physico-Mechanicall, Touching the Spring of the Air and its Effects
(1660).
Boyle and Hooke discovered several physical characteristics of air, including its role in combustion, respiration, and the transmission of sound. One of their findings, published in 1662, later became known as “Boyle's law.” This law expresses the inverse relationship that exists between the pressure and volume of a gas, and it was determined by measuring the volume occupied by a constant quantity of air when compressed by differing weights of mercury. Other natural philosophers, including Henry Power and Richard Towneley, concurrently reported similar findings about air.

Boyle's scientific work is characterized by its reliance on experiment and observation and its reluctance to formulate generalized theories. He advocated a “mechanical philosophy” that saw the universe as a huge machine or clock in which all natural phenomena were accountable purely by mechanical, clockwork motion. His contributions to chemistry were based on a mechanical “corpuscularian hypothesis”—a brand of atomism which claimed that everything was composed of minute (but not indivisible) particles of a single universal matter and that these particles were only differentiable by their shape and motion. Among his most influential writings were
The Sceptical Chymist
(1661), which assailed the then-current Aristotelian and especially Paracelsian notions about the composition of matter and methods of chemical analysis, and the
Origine of Formes and Qualities
(1666), which used chemical phenomena to support the corpuscularian hypothesis.

Boyle also maintained a lifelong pursuit of transmutational alchemy, endeavouring to discover the secret of transmuting base metals into gold and to contact individuals believed to possess alchemical secrets. Overall, Boyle argued so strongly for the need of applying the principles and methods of chemistry to the study of the natural world and to medicine that he later gained the appellation of the “father of chemistry.”

(b. Oct. 24, 1632, Delft, Neth.—d. Aug. 26, 1723, Delft)

D
utch microscopist Antonie van Leeuwenhoek was the first to observe bacteria and protozoa. His researches on lower animals refuted the doctrine of spontaneous generation, and his observations helped lay the foundations for the sciences of bacteriology and protozoology. The dramatic nature of his discoveries made him world famous, and he was visited by many notables—including Peter I the Great of Russia, James II of England, and Frederick II the Great of Prussia.

Little is known of Leeuwenhoek's early life. When his stepfather died in 1648, he was sent to Amsterdam to become an apprentice to a linendraper. Returning to Delft when he was 20, he established himself as a draper and haberdasher. In 1660 he obtained a position as chamberlain to the sheriffs of Delft. His income was thus secure and sufficient enough to enable him to devote much of his time to his all-absorbing hobby, that of grinding lenses and using them to study tiny objects.

Leeuwenhoek made microscopes consisting of a single, high-quality lens of very short focal length; at the time, such simple microscopes were preferable to the compound microscope, which increased the problem of chromatic aberration. Although Leeuwenhoek's studies lacked the organization of formal scientific research, his powers of careful observation enabled him to make discoveries of fundamental importance. In 1674 he began to observe bacteria and protozoa, his “very little animalcules,” which he was able to isolate from different sources, such as rainwater, pond and well water, and the human mouth and intestine, and he calculated their sizes.