During the process of raising with the peened side of the mallet, an external mould FGHF (fig. 101), with a needle-point P, at its vertex, is applied, to indicate its proper position with reference to the mould; and allowance is made on the height and diameter of the reflector to meet the expansion of the metal during the _hard-hammering_ which is to follow. After each course of the raising with the wooden mallets, the reflector must be annealed in the following manner:--The reflector is first damped with clean water, and its surface dusted over with a powder, composed of one pint of powdered charcoal to one ounce of saltpetre, which is applied by means of a thin flannel bag. The reflector is then put on a clear charcoal fire, where it is turned round as the powder flies off, which is an indication that the metal is duly heated. Over-heating is very injurious. When removed from the fire, the reflector is plunged into a large tub, containing what is called the _pickle_, which is a solution of one quart of vitriol in five or six gallons of water. After this it is washed with clean water, and scoured with Calais sand. The next step is to put the reflector, thus raised _nearly_ to its true form, into an iron stool, where a small hole being drilled in its vertex, a circle is described from this point with a beam-compass, so as to cut the paraboloïd to the proposed size. [Illustration: Fig. 102.] [Illustration: Fig. 103.] [Illustration: Fig. 104.] [Illustration: Fig. 105.] The reflector is next _hard-hammered_ all over (or _planished_, as it is technically termed) on the bright steel-head _a_ (fig. 103), with the planishing hammer (fig. 102); and to facilitate working, the reflector is slung in a flexible frame SS, and counterbalanced by a weight _w_, hanging by a cord over the pulleys _p_ _p_. When the reflector is all _planished_ over, the next process is the _smoothing_, which is done on the steel-head _a_, with a lighter hammer (fig. 104), muffled with fine parchment at each end. After it is smoothed comes the _finishing_, or what is called the _filling up to the mould_. This is a tedious process, and the workman requires continually to have recourse to the marble table at M, on which he lays the reflector, as shewn in fig. 105, and applies to successive portions of its surface the mould _g_ _n_, which has a needle-point centred at _n_, in the small hole drilled in the vertex. During this examination, he marks with a fine slate-pencil those portions of the reflector which do not meet the mould _g_ _n_. The parts, so marked, are gently gone over with the muffled hammer, until every point touches the mould. This last process requires great caution; for, if any part of the surface be raised above the gauge, it is hardly possible to remedy it. Such a mistake, indeed, can only be corrected by annealing the reflector afresh, and bringing it back to the true form with the mallet; but reflectors so _cobbled_ are never good. The table M (fig.