EMERALD 261 



of the design which is upon the tablet or the picture, but he must stop the point of the 

 style upon the point of the pattern into which the needle should enter, then remove it, 

 and put it down again upon the point by which the needle ought to re-enter in coming 

 from the other side of the piece, and so on in succession. To facilitate this kind of 

 reading off, the pattern upon the tablet is composed of right lines terminated by the 

 points for the entrance and return of the needle, so that the operative (usually a child) 

 has continually under her eyes the series of broken lines which must be followed by 

 the pantograph. If she happens to quit this path an instant, without having left a 

 mark of the point at which she had arrived, she is under the necessity of looking at 

 the piece to see what has been already embroidered, and to find by this comparison 

 the point at which she must resume her work, so as not to leave a blank, or to repeat 

 the same stitch. 



Explanation of Figure. 



A, lower cross bars, which unite the legs of the two ends of the frame. 



a, the six feet of the front end of the frame. 



a', the six feet of the posterior end of the frame. 



a", curved pieces which unite the cross bars A" to the uprights. 



B", handle of the pantograph. 



b, b', b", three angles of the pantograph. 



c, point of the side b b'' on which the point is fixed. 

 c'', point of the pantograph. 



D'', cross bar in form of a gutter, which unites the upper parts of the frame. 



d, fixed point, round which the pantograph turns. 



E, tablet upon which the pattern to be embroidered is put. 

 E', support of that tablet. 



e, cord attached at one end to the side b c of the pantograph passing over a guide 

 pulley, and carrying a weight at the other end. 



e', iron rod by which the tablet E is joined to its support E'. 



F, F, uprights of the cloth-carrying frame. 

 F 7 , F', horizontal sides of the same frame. 



G, four roll beams. 

 G", the piece of cloth. 



g", the strings, which serve to stretch the cloth laterally. 



This machine has not been applied for embroidering nets or muslins, as these fabrics 

 are not sufficiently close to hold the needles ; it has been hitherto used for embroider- 

 ing cloth for vests and other purposes, and silk for ladies' dresses. We learn, 

 however, that some very satisfactory experiments have been made by the Messrs. 

 Houldsworth of Manchester, which promise to lead to the successful application of 

 these machines to the^ finer description of fabrics. 



EMERALD. (Emeraude, Fr. ; Smaragd, Ger.) A precious stone of a pure green 

 colour, ranking in value next to the oriental ruby and sapphire. Although susceptible 

 of a fine polish, its hardness is considerably inferior to that of most other gems, being 

 indeed but little higher than that of quartz. Its specific gravity is also remarkably 

 low, not exceeding 275. The mineral occurs crystallised in regular six-sided prisms, 

 more or less modified on the edges and angles, and offering a tolerably easy cleavage 

 parallel to the basal plane. Heated before the blowpipe it loses its transparency, and 

 at a higher temperature fuses to a vesicular glass ; whilst with borax it forms a 

 transparent bead of a fine green colour. It is quite unaffected by acids. 



The chemical composition of the emerald, and its relation to the beryl and aqua- 

 marine, were first determined, in 1797, by Vauquelin, whose analyses showed it to be 

 a silicate of alumina, combined with a silicate of a peculiar earth, called glucina or 

 beryllia. The most recent analyses of the typical emerald from Muzo, are those by 

 M. Lewy, of which the following is the mean : 



Silica ....... . ; . 67'9 



Alumina 17'9 



Glucina , . 12-4 



Magnesia *'-/ . . 0'9 



Soda 0-7 



Slight traces of sesquioxide of chromium are included in this analysis, but, 

 according to Vauquelin's experiments, the amount of this chromic oxide may rise as 

 high as 3'5 per cent. 



Since this oxide is well known to communicate a fine green tint to glass, the colour 

 of the emerald was naturally referred to its presence ; but this opinion was contra- 

 dicted a few years ago by M. Lewy, who maintained that the extremely minute trace 



