The early twentieth century was a period of dramatic change in physics, as Newtonian mechanics was challenged by the new theories of relativity and the quantum. While we now describe the former as classical and the latter as modern physics, these categories were not self-evident. Even as late as the 1920s, there were not clear definitions of ‘classical’ and ‘modern’ physics, and there was no consensus as to the place of the former in the future of the discipline. In this paper, I explore how British physicists managed the transition from ‘classical’ to ‘modern’ through their scientific and ‘public’ publications in the 1920s. I consider the physicists responsible for managing the Royal Society’s Proceedings, and look at how they made judgements over what counted as a ‘valuable’ scientific contribution. Central to their assessments of a paper’s suitability for publication was its incorporation of what they defined as ‘modern’ physics, with ‘classical’ offerings often deemed unhelpful to the progress of physics. In contrast, the editors of the Philosophical Magazine welcomed ‘classical’ physics, and the journal served as a home for many papers that the Proceedings would not publish. In the ‘public’ sphere, meanwhile, the worth of ‘classical’ physics was promoted almost unanimously in positive terms. In their popular books, physicists who engaged with wider audiences were careful to portray ‘classical’ and ‘modern’ physics as working in harmony, denying any claims of a ‘destructive’ revolution or new theories having superseded the work of Newton. This public reverence towards Newton, and attempts to rescue ‘classical’ physics from disrepute, was part of an effort to present the discipline as stable and consequently trustworthy. I analyse the work of two physicists in particular: Oliver Lodge and James Jeans. The case of Jeans provides a clear example of the contrast between ‘public’ and ‘professional’ evaluations of ‘classical’ physics. As Physical Secretary of the Royal Society throughout the 1920s, Jeans rejected papers that were not sufficiently ‘modern’, but in his public pronouncements he emphasised the continuing importance of Newtonian mechanics. Oliver Lodge, staunch defender of the ether, was an editor of the Philosophical Magazine, and encouraged the type of physics dismissed by Jeans. In Lodge’s popular books and articles, he depicted physics as being in a state of transition, awaiting a ‘Newton’ that would connect the ‘classical’ to the ‘modern’. In both of these cases, issues of trust and expertise are important. Both Jeans and Lodge had trusted contributors, whose work they would publish without question. And in the ‘public’ sphere, Jeans and Lodge acquired the reputation of ‘experts’, trusted to teach the public about physics. Relationships of trust directed the publication of ‘classical’ and ‘modern’ physics throughout the 1920s, revealing a continuity between professional and ‘popular’ publishing. While the content of ‘popular’ physics might differ considerably from that published in the Proceedings, both were influenced by similar forces.