A founder-member of the Austrian Meteorological Society (1865), Mendel actively contributed as an observer on his own account, [i], and as an organiser of meteorological observations in Moravia. The majority of his publications are in fact devoted to meteorology. The sheet of meteorological variations, dated October 1878 [i], shows the meticulous work of registration and comparison of data. The collection and study of meteorological data was based on two operations which were to be fundamental to Mendel's own method of research: these were the observation of natural phenomena, and the statistical calculation of variations - combinatory mathematics. This branch of mathematics deals with the different outcomes that can occur when a number of observations are made, and each observation can fall into one of several categories. This was relevant to Mendel's work, because he was studying categorical traits (smooth versus wrinkled, etc), and he was counting the proportions of observations that fell into each category. Combinatory mathematics has long been key to astronomical observations, and nowadays it is applied to DNA testing. Combinatory mathematics is relevant to disciplines such as astronomy and experimental physics.
 Astronomy was another important field of interest for Mendel [i], whose copy of Popular Astronomy (Populäre Astronomie) by J.J. Littrow (1825) [i] contains his own annotations on the relative positions of the sun and the earth. Mendel's professor of physics in Vienna was Christian Doppler (1803-1853), the head of the new Institute of Physics - now famed for his definition of the "Doppler effect", originally an optical phenomenon in astronomy and one that explains how the frequency of sound seems to change as the source of the sound moves towards and away from us. Doppler championed the principles of combinatory and probability theories in the applied sciences, with special reference to physics [i].
Mendel's own method of research - based on the identification of significant variables, isolating their effects, measuring these meticulously, and eventually subjecting the resulting data to mathematical analysis - is therefore directly informed by contemporary theories of mathematics, statistics and physics, which were taught and published in the towns of the Austrian-Hungarian Empire.
 "...no-one can say why the same peculiarity in different individuals....is sometimes inherited and sometimes not so: why the child often reverts in certain characters to its grandfather, or other much more remote ancestor; why a peculiarity is often transmitted from one sex to both sexes, or to one sex alone, more commonly but not exclusively to the like sex." from Charles Darwin, On the Origin of Species by Means of Natural Selection, 1859
Theories of mathematics, statistics and physics as applied to biology were foreign to Charles Darwin who, in his Variation of Animals and Plants under Domestication (1868), [i] adopted and adapted the old theory of "pangenesis", first put forward by Hippocrates (460-377 BC). According to this theory, minute particles from every part of the body entered the seminal fluid of both parents, and by fusion gave rise to a new individual with both parents' traits. Mendel's theories involved discrete factors amenable to combinatory mathematics. These theories were foreign to Darwin who explained forms of sexual and asexual reproduction ("parthenogenesis") by the blending of continuous elements. We now know that Mendel was aware of Darwin's theory of pangenesis, and that he disagreed with it (as did Darwin's close friends, T.H. Huxley and John Lubbock).
 New Ideas About Species
"Nature intended that a sexual intercourse should take place between neighbouring plants of the same species." from Thomas Andrew Knight (1759-1838), An Account of some experiments of fecundations of vegetables, 1799
Within the context of the study and classification of nature and the sexuality of plants, Carolus Linnaeus (1707-1778), one of the leading botanists of the 18th century, occupies a special place. He is renowned for his system of plant classification based on their sexual organs, and for his experiments with plant hybrids, which led him to exploring the possibility of the appearance and disappearance of new species in nature. After Linnaeus, various hypotheses were formulated in relation to hybrids [i]. J.G. Kölreuter (1733-1806) confirmed experimentally the theory of the sexuality of plants, and was the first to carry out experiments purely as a scientific exercise rather than with the aim of obtaining better crops. Like Aristotle (384-322 BC), Kölreuter [i]believed that both parents produced a fluid semen which blended in the off-springs, whose, characteristics were a "mixture" of those of the parents. However, one century before Mendel, Kölreuter was responsible for developing the principle of the "segregation" of characters: he noticed that different characters were inherited independently of each other, an observation which is fundamental to Mendel's own theory.
 Another key figure in the study of hybrids was the German botanist, F. Carl Gärtner (1772-1850), who worked on the crossing of peas, tobacco, and maize - carrying out more than 10,000 experiments on 700 species of plants, and winning a prize set by the Haarlem Academy of Sciences in 1830 for the demonstration of the sexuality of plants. Referring back both to Kölreuter and Knight, Gärtner observed that when different species of plants were cross bred, to produce hybrids, characteristics from each of the parent plants would combine variably in the progeny (variable hybrids). Nevertheless he still believed that species are constant and that it was not possible to transform one species into another.
These and other studies of the mechanisms of heredity suggested a new concept of species which, in the 19th century, carried deep religious implications. To argue against the fixity or constancy of the species, and to demonstrate that new species could be formed by artificial fertilisation, was also to question that all existing and possible species had been eternally created by God. The making of new species through human intervention was even more potentially blasphemous than Darwin's concept of evolution. One wonders what Mendel the religious man would have thought of this. The absence of any related documentation leaves this question unanswered.
Meteorology instruments and texts
Meteorology records
Astronomy and physics
Theories of species