Page:Popular Science Monthly Volume 27.djvu/49

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The slow and painful work of months is in this way presented to a class in a few minutes, and the practical lessons caught at a glance. Indeed, in most problems the difficulty is to put others in possession of

PSM V27 D049 History of price relationship between silver and gold.jpg

the facts which one is about to discuss. For this purpose, charts are the labor-saving machine of statistics. They can be made on common white cotton cloth (called sarcenet), which receives ink (black or red or blue) or water-colors; or on heavy manila paper, made large