Arguably the most prominent atomic theory, first published in the opening decade of the nineteenth-century was that of John Dalton. Within it, Dalton argued 'each element had a unique atom associated with it' (Bowler, Morus, 2005), and these atoms were indivisible and indestructible. The atoms of a particular element are identical to each other, formed compounds in simple ratios when two or more different elements' atoms joined together and rearrange during a chemical reaction. As a result of these findings, Dalton was able to calculate the relative weights of atoms. However, given the minute size of atoms it took some time for these propositions to be accepted. There were three major angles from which many Victorian scientists rejected Dalton's atomic theory; those who wanted to use mathematical laws, others who looked to exclude unobservable entities and those who refuse to believe that there was a variety of ultimate elementary materials. With regard to the opening objection concerning mathematical laws, Herschel and his predecessors, namely George Pearson, argued that the theory was 'the law of definite proportions, which is the same thing presented in a form divested of all hypothesis' (Knight, 1967). However, what Herschel really wanted was a mathematical form of science and thus he questioned why Dalton had used a hypothesis to explain these laws. The atomic theory therefore failed to convince those who wanted to make the subject mathematical. Whether it was Benjamin Brodie's Calculus of Chemical Operations or Ostwald's thermodynamic physical chemistry, they both agreed that the 'chief task of scientific theory is the discovery of the laws of phenomena' (Bunge, 1963). Because Dalton added nothing to 'seventeenth-century corpuscularian predecessors' (Knight, 1967) but definite proportions, 'his theory imply pushed the explanation back one stage without adding anything to it' (Knight, 1967). The overall consensus is that Dalton seemed confused as to whether his theory 'was a theory of matter, that everything is made up of indestructible atoms of different kinds, or a theory only of 'chemical atoms' (Knight, 1967).
William Wollaston was one of Dalton's initial supporters and originally he appeared atomistic, agreeing with Dalton's observations that 'in all cases the simple elements of bodies are disposed to unite atom to atom' (Knight, 1967). However, after further consideration, Wollaston published a paper describing his slide-rule and disagreed with Dalton's assumption that by estimating 'the relative weights of equivalents…[we can know] the aggregate weights of a given number of atoms, and consequently the proportion which the ultimate single atoms bear to each other' (Knight, 1967). Wollaston doubts the existence of atoms due to the fact there is no clear method of knowing which compounds are binary or tertiary, therefore considering it as impossible to be certain of a true atomic weight. In this way, 'the atomic theory appeared to postulate unnecessary entities whose weights were arbitrary and whose arrangements were inaccessible' (Knight, 1967). In response to this, Dalton looks to change the meaning of the word 'atom', changing it from meaning 'that which could no longer split…to that which if splits yields something qualitatively different' (Knight, 1967), and supposes that elements were made up of simple atoms. In an attempt to make the world appear more simple, Dalton uses the term 'atom' not only to refer to the particle of an element which has a chemical nature and enters into chemical combination with other particles, but also in the sense of 'solid and indivisible ultimate particles. Dalton thus drew no distinction between the chemical elements and the primordial physical atoms' (Harman, 1982). By 'admitting a considerable number of irreducibly different elementary bodies' (Knight, 1967), he lost the support of many scientists including Wollaston who viewed atoms as unnecessary, whilst following scientists such as Faraday 'rejected corpuscular atoms on the evidence of new experimental phenomena' (Knight, 1967).
Meanwhile, scientists such as Prout and Dumas 'rejected simple atomism for a molecular theory of matter on the grounds of the interpretation of the chemical laws of combination' (Knight, 1967) whilst William Whewell rejected atoms on the basis that any 'inquiry into the fundamental structure of matter – to find out of it was made up of discrete units like atoms or was continuous and indefinitely divisible, for example – was beyond the scope of experiment' (Bowler, Morus, 2005). As a result of this lack of proof Davy 'made a careful distinction between belief in a metaphysical theory of atoms and the experimental evidence of combining proportions' (Brock, 1993) and went as far as to state that 'unobservable entities should be rigorously excluded from the science' (Knight, 1967). Despite appreciating that the term 'atom' is useful in denoting relative atomic weights, Whewell warns that the 'use of the 'atom' need not be understood as implying assent to the hypothesis of ultimate, indivisible particles' (Harman, 1982). Therefore, these atomic theories could never progress further than the title of a theory.
In his account of electrochemical atomic theory, Berzelius 'introduced a new conventional nomenclature into chemistry' (Bowler, Morus, 2005). He represented the various elements using letters and abbreviations and placed them in an order with the 'most electropositive element being written first' (Bowler, Morus, 2005) when two elements combined. However, Dalton rejected this on the basis that he believed that conventional symbols 'undermine[d] acceptance that chemical atoms had a real physical existence' (Bowler, Morus, 2005). It is this notation which Dalton used in order to emphasise atoms' physical reality which came under attack. Victorian scientists never accepted chemical atoms as having realistic properties, rather they were 'just a convenient way of talking about chemical reactions and the proportions in which elements combined' (Bowler, Morus, 2005). Chemists therefore regarded atomic theory 'as no more than useful empirical tools' (Bowler, Morus, 2005).
There was also great confusion regarding the empiricism of chemistry as 'different chemists made different assumptions concerning the calculation of combining weights' (Brock, 1967). Standards for atomic weights changed, making international communication a struggle. This was compounded by Dumas' vapour densities in the 1820s which proved that 'molecules of simple gases might divide during combination' (Brock, 1967). This, coupled with later studies of the densities of several other elements, made the concept of atoms so confusing that even Dumas wrote 'if I were master I would efface the word atom from science' (Brock, 1967). Benjamin Brodie, on the other hand, dismissed the existence of atomism from a philosophical and simplicity basis. To achieve this, he ridded chemistry of atoms by also introducing a new language using the Greek alphabet, in this way putting 'chemistry back onto its empirical feet' (Brock, 1967). He believed that by installing this method, chemists were able to 'give operational descriptions of the weight and volume changes that occurred during chemical reactions' (Brock, 1967) rather than accounting for these changes in terms of atoms and molecules.
Another major critic of Dalton's theory of atomism was Humphry Davy who stressed the unity of matter. Dalton believed that different elements were made up of different atoms, stating that the atoms of iron are all identical and the atoms of hydrogen were all identical, therefore implying that 'different kinds of atoms were irreducible different' (Knight, 1967). By claiming this, he is directly opposed to the Boscovichean tradition that 'all matter was made up from identical atoms, differently arranged' (Knight, 1967), and those who understood this tradition opposed the atomic theory throughout the Victorian period. While Davy positively described Dalton's theory of laws of definite proportion as useful, he went on to argue that 'statements about atoms were both hypothetical and useless' (Knight, 1967). This judgement was held by many scientists during the Victorian era; the Irish chemist Michael Donovan was one of these and he argued that both the 'atomic theory and the law of equivalents involved the same assumptions, and therefore were equally hypothetical' (Knight, 1967). The overriding view held by scientists of this age was that atomic theory is helpful but not necessarily true.
Several Victorian scientists debated and considered the criteria for what constitutes a discovery of an unobservable entity. Theodore Arabatzis delves into this issue, outlining the various stances which these scientists took in determining what comprises a discovery. Many of them would have adopted an antirealist perspective, 'that is, maintain that one has to be at least agnostic with respect to the existence of unobservable entities' (Arabatzis, 2006). By adopting this mind-set, Victorian scientists believed that the discovery of unobservable entities never happened and has no truth behind it – 'the unobservable entity is a convenient fiction' (Arabatzis, 2006). Thus, the existence of atoms would have been refuted on these grounds and the scientists would argue that any 'existence claims concerning the unobservable can never be sufficiently justified' (Arabatzis, 2006). As a result, 'the majority of chemists, while using the term 'atom', refused to commit themselves to the real existence of such bodies' (Knight, 1967).
Finally, one of the most famous anti-atomists in the nineteenth-century was the French chemist Marcelin Berthelot. Within his paper he attacks Dalton's atomic theory, conceding that 'atomism might be acceptable as a system of conventions, but he feared the power of such conventions in constructing a realistic picture of atoms which was not warranted empirically' (Nye, 1980). He made this clear by warning his readers not to mistake the ''real' science with its idiosyncratic contemporary form' (Nye, 1980) and he understood that language controls the human mind, containing the language of atoms within this bracket. In a lecture at Collège de France he picked apart the atomic theory's physical hypotheses and asked his audience if anyone had ever seen an atom. Moreover, he refused to use 'atomic notation and values for atomic weights, because…the notation did not conform to experimental relations of volume and gaseous mercury and cadmium' (Nye, 1980). Similar to the previous paragraph, Berthelot's main motivation for his anti-atomist stance was due to the fact that the 'hypotheses of the atomic theory…proposed unseen entities' (Nye, 1980). The models of atoms which physicists conjured up were too imaginative and hypothetical for Berthelot, claiming that to regard the atom as 'solid, ponderable…a subtle ethereal fluid in motion is 'a symbol, a fiction….[just as the]…electric, magnetic, calorific and luminous fluids that one allowed at the beginning of the century…have now no more reality in the eyes of contemporary physicists than the four elements'' (Nye, 1980).