The fluid is non-toxic and non-hazardous, an inert oil/hydrocarbon mixture like mineral oil: Galileos are carefully packaged. The cylinder walls are laboratory grade glass, so sturdiness isn't an issue. A four-color cardboard box sleeve surrounds a form-fitted foam case that virtually guarantees safe arrival: This fascinating, functional instrument is the point at which science meets art. Four hundred years ago Galileo discovered that specifically weighted floating bubbles would predictable rise or sink in a liquid as the temperature of that liquid is changed. These decorative glass reproductions of Galileo's discovery have glass floats precisely weighted 6 gram increments suspended in a clear, environmentally safe, non-toxic liquid. Simply read the tag on the lowest floating bubble to read the temperature: The 17 inch measures every 4 degrees from 60 F to 96 F and is accurate to within 2 degrees with eleven floats.