To make a perforated square zinc top for an aquarium, that could be taken off and put on as required, commence by drawing a plan and elevation (Figs. 1 and 2) to the required size. Divide the semicircle d d (Fig. 2) into six equal parts, and draw lines at right angles to C C to pass through the division points b b; also join the division point c to C and d to C. From any point along X Y erect the perpendicular o o, and from 0 mark off lengths corresponding to b B, c C, C d (Fig. 2); join these points to o, and the lengths found, Bo,Co,Do, will be the true slants of the lines b B, c C, C d (Fig. 2). To work the pattern, draw a straight line equal in length to C C (Fig. 2): mark upon this line a centre point A (Fig. 3), and mark on either side of A divisions corresponding to AB ( Fig. 2). From A, B, B (Fig. 3) draw lines at right angles to C C, and mark on these lines from the point A, a length equal to D' d' (Fig. 1), and from B, B lengths equal to o B (Fig. 1). Next use C as centre, and with radius C o (Fig. 1) draw an are; with b c (Fig. 2) as radius and b (Fig. 3) as centre, cut the arc first drawn to obtain the point c; again use C as centre on both sides of the pattern, and with radius oD (Fig. 1) draw an arc; with the division length cd (Fig. 2) cut the arc so as to obtain the point d. Now take the length C D (Fig. 2) as radius, and again using C (Fig. 3) as centre, draw an arc; with D' d' (Fig. 1) as radius and d on the pattern as centre, cut the arc first drawn. Join the intersecting arcs d~D by a straight line, and also join D C. Draw a curve through the intersecting arcs d, c, b, a,b, c, d,to complete the half pattern with seams placed in the centre of the sides at D d, D d. When making the top, bend the corners CC upon any sharp-edged tools until the sides form a right angle with the end; the semicircle forming the half top can be brought to shape by pressing the perforation to a circular shape with the thumb. If the two halves are to be grooved together, an equal allowance for the groove will be necessary on each side of the pattern; if solderiug is adopted, then one lap, as shown, will do.

Pattern for Aquarium Top.