Isaac Newton proposed a mechanical universe with small solid masses in motion.
John Dalton proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
Michael Faraday studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. He was not a proponent of atomism.
J. Plucker built one of the first gas discharge tubes
Lother Meyer lassified elements into six families by their valence.
Dmitri Mendeleev arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law
James Clerk Maxwell
James Maxwell proposed electric and magnetic fields filled the void.
Sir Williams Crookes
Sir William Crookes discovered that cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass.