Page:A Brief History of South Dakota.djvu/43

 CHAPTER VII

along the way Lewis and Clark took celestial observations to ascertain the latitude and longitude. They also kept a record of the temperature, with a mercury thermometer made for them in St. Louis by a French physician and scientist named Dr. Sauguin. They fell in with the doctor when they arrived at St. Louis; and he gave them much valuable information and assistance and told them how important it was that they should have a thermometer. The good captains had not the slightest idea what a thermometer was, but the little doctor hurried about to find the materials out of which to make the instrument. Not in the Mississippi valley could he find the glass or the quicksilver, till finally he bethought himself of his wife's French plate-glass mirror, and, in spite of her protest, he scraped the quicksilver from the back of it, melted up the mirror, and made from it the stem of the thermometer, into which he poured the quicksilver he had scraped from the looking-glass. This was soon properly graduated, or scaled to degrees of heat and cold, and, judging by what we now know of the temperatures of the Missouri valley, was reasonably accurate. From such circumstances as the foregoing the student will understand how primitive was the outfit of the explorers. 37