inch; these are indicated by the dotted lines, which divide the double paper into four triangles, each of which is to be again folded into eighths, and care must be taken that all the folds are made the same way, that is, projecting to the same side of the paper. When complete, the double and creased paper will appear as _Fig. 7_. Now divide each eighth into half, by a fold in the _opposite_ direction to those previously made, when it will be found that the whole will fold up like a paper fan; the projecting loose ends which are formed by the corners _b_, should be cut off, and the double sides separated for the first time by blowing them apart, when the whole may be readily opened out as in _Fig. 8_. In making this filter, which takes a much less time than to follow the description, two precautions are requisite. The folds should be made at once with one firm pressure, and not with a series of rubbings; and all the creases should stop short of the middle, otherwise a hole will be made at that point, long before the filter is completed. The advantages of this filter are, that it exposes a large surface for the liquid to pass through; and from its only being in contact with the funnel where the angles project, the current flows away readily. [Illustration: _Fig. 8._] The best means for filtration of water, and the construction of water filters will be treated of when we speak of the “domestic manipulation” connected with that liquid. IV. THE MANUFACTURE AND USE OF CEMENTS. The term cement, includes all those substances employed for the purpose of causing the adhesion of two or more bodies, whether originally separate, or divided by an accidental fracture. As the substances that are required to be connected together are exceedingly various, and differ very much in their properties as to texture, &c., &c., and as the conditions under which they are placed, with regard to heat and moisture, are also exceedingly variable, a number of cements, possessed of very different properties, are required; for a cement that answers admirably under one set of circumstances, may be perfectly useless in others. A vast number of cements are known and used in the various arts; but they may all be referred to a few classes, and our object in this paper will be to describe the manufacture and use of the best of each class, and also to state what are the general principles upon which the success or failure of cementing usually depends.