Alfred Marshall explored a scientific method for theorising complex economic phenomena using mechanical and biological analogies. Moreover from his very first book The Economics of Industry Marshall paid attention to the efficacy of a science of tendencies to understand real economic movements. To clarify this, this paper begins by reviewing a methodological problem suggested by Thorstein Veblen, concerning which of Marshall’s economics should be regarded as ‘quasi-evolutionary’. Critically Veblen considered Marshall’s approach to economic progress could not avoid assumptions of a natural law and normality, even though Marshall analyzed the tendency of economic change produced over the ultra-long-term. However, we focus on the approaches Marshall found most convincing, which were based on eighteenth and nineteenth century scientific methods proposed by Cournot, John Herschel, and William Whewell. We examine the methodological significance derived from the analogies of astronomy and tidology over the secular term. Specifically, Marshall investigated the analysis of wages as a science of tendencies to realise fair wages through conciliation, where the influence of time, region, and custom were considered. Therefore, this article demonstrates how Marshall applied a non-Newtonian method based on tidology to the study of secular movements in economic society to develop his understanding of the organic growth of economy scientifically.