The strongest are:

Theory that atoms exist, i.e. matter is not continuous.

Much before atoms were thought to be "experimentally real", chemists from the 19th century already used "conceptual atoms" as units for the proportions observed in macroscopic chemical reactions, e.g. $2H_2+O_2\leftrightarrow H_{2}O$. The thing is, there was still the possibility that those proportions were made up of something continuous that for some reason could only combine in the given proportions, so the atoms could only be strictly consider calculatory devices pending further evidence.

Subtle is the Lord by Abraham Pais (1982) chapter 5 "The reality of molecules" has some good mentions. Notably, physicists generally came to believe in atoms earlier than chemists, because the phenomena they were most interested in, e.g. pressure in the ideal gas law, and then Maxwell-Boltzmann statistics just scream atoms more loudly than chemical reactions, as they saw that these phenomena could be explained to some degree by traditional mechanics of little balls.

Confusion around the probabilistic nature of the second law of thermodynamics was also used as a physical counterargument by some. Pais mentions that Wilhelm Ostwald notably argued that the time reversibility of classical mechanics + the second law being a fundamental law of physics (and not just probabilistic, which is the correct hypothesis as we now understand) must imply that atoms are not classic billiard balls, otherwise the second law could be broken.

Pais also mentions that a big "chemical" breakthrough was isomers suggest that atoms exist.

Very direct evidence evidence:

Less direct evidence:

Subtle is the Lord by Abraham Pais (1982) page 40 mentions several methods that Einstein used to "prove" that atoms were real. Perhaps the greatest argument of all is that several unrelated methods give the same estimates of atom size/mass:

Subtle is the Lord by Abraham Pais (1982) page 85:so it is quite cool to see that organic chemistry is one of the things that pushed atomic theory forward. Because when you start to observe that isomers has different characteristics, despite identical proportions of atoms, this is really hard to explain without talking about the relative positions of the atoms within molecules!

TODO: is there anything even more precise that points to atoms in stereoisomers besides just the "two isomers with different properties" thing?

Was the first model to explain the Balmer series, notably linking atomic spectra to the Planck constant and therefore to other initial quantum mechanical observations.

This was one of the first major models that just said:

It still treats electrons as little points spinning around the nucleus, but it makes the non-classical postulate that only certain angular momentums (and therefore energies) are allowed.

Bibliography:

Nihonium is a synthetic chemical element with the symbol Nh and atomic number 113. It is one of the superheavy elements in the periodic table and was first officially reported in 2004 by a team of Japanese scientists at the RIKEN institute. The name "Nihonium" is derived from "Nihon," which is one of the ways to say "Japan" in Japanese, reflecting the element's discovery in Japan.

Taqi ad-Din Muhammad ibn Ma'ruf, often referred to simply as Taqi ad-Din, was a prominent Arab astronomer, mathematician, and engineer during the 16th century. He was born in 1526 in Damascus in the Ottoman Empire (modern-day Syria). He is best known for his contributions to astronomy and for establishing the first observatory in the Islamic world, the Maragha Observatory, which played a pivotal role in the development of astronomical research.

The Pearson distribution, or Pearson system of distributions, is a family of continuous probability distributions that are defined based on moments, especially how the shape of the distribution is determined by its moments (mean, variance, skewness, and kurtosis). This system was introduced by Karl Pearson in the early 20th century, and it encompasses a wide range of probability distributions, including the normal distribution, beta distribution, and skewed distributions.

Data-Link Switching (DLSw) is a networking protocol that helps in the interconnection of different types of network protocols, specifically to facilitate the transmission of data over WAN (Wide Area Network) links. It was primarily developed to enable the encapsulation and transport of legacy protocols, such as IBM's SNA (Systems Network Architecture), over TCP/IP networks.

Edward H. Sussenguth was a renowned American marine biologist, particularly recognized for his work in the field of ichthyology, the study of fish. He significantly contributed to our understanding of fish taxonomy and ecology, particularly in the Atlantic Ocean. Sussenguth's research included extensive studies on the life histories and populational dynamics of various fish species. His work is important for both academic research and practical applications in fisheries management and conservation.

IBM DISOSS, or IBM Dynamic Infrastructure Services for Open Systems Software, is a set of software and tools designed to help organizations manage and optimize their IT infrastructure. It focuses on improving the performance, security, and scalability of systems, particularly in dynamic and virtualized environments. DISOSS enables better resource management, automates tasks, and enhances the overall efficiency of IT operations, supporting both traditional and cloud-based architectures.

Synchronous Data Link Control (SDLC) is a bit-oriented synchronous communication protocol used for transmitting data over point-to-point and multipoint links. It was developed by IBM in the 1970s as a way to facilitate reliable and efficient data transmission in telecommunications. ### Key Features of SDLC: 1. **Synchronous Communication**: SDLC operates synchronously, meaning that data is transmitted in a continuous stream along with a clock signal.