Baby Names Beginning With "Z": Meaning: Vigorous, Alive?

Questions

In what year did John Ericsson make the first realistic application of solar energy using parabolic solar reflector to drive caloric engine on steam boiler?

Last names of the two men who invented spectrum analysis?

In what year did Kirchhoff & Bunsen invent spectrum analysis?

Who invented the stethoscope?

In what year did Rene Laennec invent the stethoscope?