Biomedical subjects

H A Snelders

Publications and source records attributed to H A Snelders.

At least 19 recordsLinked to original sources

PubMed1997

[Are liquid crystals living organisms?].

In 1888 the Austrian botanist F. Reinitzer made the observation that the solid compound cholesteryl-benzoate changes - when melting at 145.5 oC - into a cloudy liquid, that however, turns into a clear liquid at 178.5 oC and higher temperatures. The cloudy liquid seemed to be doubly refracting. Soon a number of these so-called 'liquid crystals' were discovered; in 1908 D. Vorländer, professor of organic chemistry at Halle, described more than 250 of these substances. It was O. Lehmann, professor of physics at Aachen (1885), Dresden (1888) and Karlsruhe (1889), who immediately after Reinitzer's observation began a systematic study of these liquid crystals. In The Netherlands the Amsterdam professor of physican chemistry H. W. Bakhuis Roozeboom was interested in liquid crystals, in particular because of their place in his phase system. F.M. Jaeger, at that time teaching chemistry in a secondary school in Zaandam (near Amsterdam) and working as an unpaid university lecturer at the Amsterdam university (by recommendation of Bakhuis Roozeboom), investigated liquid crystals (1906), as did a number of doctoral students (A.C. de Kock, 1903; A. Prins, 1907). At the university of Utrecht L.S. Ornstein, professor of physics, gave the study of liquid crystals a prominent place in his research programme. The discovery of liquid crystals, which seemed to be able to grow, move, divide, copulate, and so on, led to a discussion on the nature of these substances. Time and again Lehmann called them 'apparently living crystals', although without considering them as 'real living beings'. In his book Flüssige Kristalle und die Theorien des Lebens (1906), Lehmann proved to be an obvious adherent of the monistic views of the biologist E. Haeckel. Haeckel considered the existence of liquid crystals as proof of the unity between the inorganic and the organic world that he believed in so strongly. In his last book, Kristallseelen. Studien über das Anorganische Leben (1917), he considered liquid crystals a real form of life, as did F. Rinne, professor of mineralogy and petrography, as late as in the nineteen thirties.

Crystallography↗

PubMed1995

[Not Available].

Dutch science flourished in the late sixteenth and in the seventeenth century thanks to the immigration of cartographers, botanists, mathematicians, astronomers and the like from the Southern Netherlands after the Spanish army had captured the city of Antwerp in 1585, and thanks to the religious and the socio-economic situation of the country. A strong impulse for practical scientific activities started from the Reformation, mainly thanks to its anti-traditional attitude, which had an anti-rationalistic tendency. Therefore, in the Northern Netherlands there was no 'warfare' between science and religion and the biblical arguments leading to Galileo's condemnation were not used. Although the growth of the exact sciences and of technology in the late sixteenth and the seventeenth centuries in Protestant circles may be partly attributed to the expansion of trade, industry, navigation and so on, this does not explain why there was also at the same time a great interest in subjects as botany and zoology, which had no immediate economic utility. There were discussions about Copernicanism and Cartesianism. So a number of astronomers and theologians rejected the earth's movement on scientific and religious grounds, but there were also those who did not reject the Copernican system on biblical grounds. In the seventeenth century there was much discussion between science and religion in the Northern Netherlands, but that discussion was not followed by censure by the Church of the State. In the Republic there was a large amount of intellectual freedom in the study of the natural sciences, thanks to practical and ideological considerations. In the eighteenth century the seventeenth century tension between science and religion changed into a physicotheological natural science. It was believed that investigations into the workings of nature should lead to a better understanding of its Creator. So Bernard Nieuwentijt in his well-known book: The right use of world views for the conviction of atheists and unbelievers (1715) intended to prove the existence of God on the basis of teleological arguments.

History, 16th Century↗

PubMed1994

[Reasoning by analogy in chemical history: fallacies and guidelines].

In chemistry (and natural science in general) reasoning in terms of analogy may be of great practical value as well as of theoretical significance. At the same, however, the use of analogy is risky and the results are uncertain. In alchemy and iatrochemistry analogies between the living and the non-living nature have been carried too far. At the end of the 19th century an analogy was drawn between chemical phenomena and the Darwinian theory of evolution. Another example of an overexaggerated analogy can be found in Lavoisier's theory of acids, where oxygen was considered to be the general principle of acidity. Reasoning by analogy is mostly based on an inner conviction. It leads to provisional predictions in such cases where the required facts are not, or incompletely, at our disposal.

Chemistry↗

PubMed1993