Slipher developed spectrographic methods that allowed researchers to see a Doppler effect in the distances of what were then called “spiral nebula,” what we today call galaxies. Simply put, by measuring the longer wavelength red shift (objects moving away) and shorter wavelength blue shift (objects moving closer), Slipher demonstrated that the universe was not static.
The gap between the two flasks is partially evacuated of air creating a near vacuum which significantly reduces heat transfer by conduction or convection