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 Rh degrees higher. The want of it in various departments of the arts and manufactures is already sensible. The valves of steam engines, for example;—the tables of printing presses,—stereotype plates,—surface plates,—slides of all kinds, require a degree of truth much superior to that they generally possess. In these, and a multitude of other instances, the want of truth is attended with serious evils. In the case of the slide valves of steam engines, there is occasioned a great loss of steam power, and also an immense increase of wear and tear. In stereotype printing, inaccuracy of the plates renders packing necessary to obtain a uniform impression. A vast amount of time and labour is thus sacrificed, and the end is, after all, but imperfectly attained.

The extensive class of machinery,