Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: certain that the necessary heat, at least, is attained. By removing one, two or three of the flat pieces, it will be found that, in a little time, the position of the mercury becomes steady, and is not aifected by closing one of the holes or unclosing another. The steadiness of the boiling-point, whether the steam issues languidly or with considerable vehemence, is rather a puzzle to me, but the fact is quite certain." In Plate I. fig. 5, is represented the cylindrical boiler : is the cork through which the thermometer tube is inserted into the steam without touching the water; b is the escape tube; i the spirit-lamp; w the water used, which must be pure rain or distilled water, for the admixture of any salt would raise the boiling-point. 39. The Scale. Fahrenheit's division.—We have now on the scale two fixed points, and unless we aim at extreme nicety, we have only to divide the space between them into a certain number of equal parts, extending the divisions above the boiling-point and below the freezing, and the scale of the thermometer will be complete. In the thermometer in general use in England, this space is divided into 180 portions called degrees; it derives its name from Gabriel Fahrenheit, a native of Dantzic, who fixed his zero at the point of the lowest cold observed in Iceland, which wassupposed to be as low a temperature as was likely to become the subject of philosophical investigation : this zero is 32 below the freezing-point, and 212 below the boiling-point of water. The advantages of this scale, which it possesses above others, are, that the observer, especially in meteorology, is very seldom troubled with negative degrees, which do not commence till the extreme cold of 0, or 32 below freezing, has been reached ; as the divisions moreover are more numer...