Fuel oil conservation. Logs snapping in the fireplace mean fuel conservation as well as cozy evenings at home. On crisp days… https://www.rawpixel.com/image/12307210/image-plant-person-artFree Image from public domain licenseAn alchemist in his laboratory. Oil painting by a follower of David Teniers the younger. https://www.rawpixel.com/image/14016541/image-face-person-bookFree Image from public domain licenseA physician examining a urine-flask. Oil painting by Justus Juncker. https://www.rawpixel.com/image/14004029/physician-examining-urine-flask-oil-painting-justus-junckerFree Image from public domain license