636 SUMMARY OF CURRENT RESEARCHES RELATING TO 



layers of analogous form and arrangement serve in certain cases like that 

 of the animal crystalline lens, and in other cases simply superposed serving 

 for the production of complete achromatism, but also under certain 

 circumstances arranged in a manner contrary to the preceding arrangements 

 they will serve to produce the maximum of chromatism and the separation 

 of the chemical focus or optical focus, or even of the entire or partial 

 spectrum or the neutral tints, &c., for the production of the effects of 

 polarization and interference." 



" Fig. 22 represents a double convex lens formed of concentric layers, 

 the chemical and optic foci of which meet at the same point without 

 aberration of any kind. Fig. 23 is a double concave of the same 

 arrangement. Fig. 24 represents an object-glass composed of a series of 

 three lenses achromatized by concentric layers superposed, and in the form 

 of an ellipsoid, hyperboloid, or paraboloid, or simply a spheroid." 



Making the Lenses. — Although somewhat lengthy, we transcribe this 

 part of the patent in full, as it is by far the most " original " portion of the 

 patentee's description. "In order to make the small Microscope lenses, 

 especially for the first or object-glasses as well as the eye-glasses of the 

 others, liquid glass is placed in a small pot or crucible formed as shown in 

 fig. 25. The vitreous matter is passed through a small opening o, and 

 by means of a blower it is blown in a state of fusion ; by this means it is 

 granulated or divided into round granules, the size of which is in pro- 

 portion to the size of the opening o and of the blower, and to the force 

 with which the air or gas is projected through the fused material. Instead 

 of air or gas high-pressure and superheated steam may be employed, or 

 a stream of water or other liquid at a high pressure and at a suitable 

 temperature. If these granules should be required to be slightly flattened 

 on one side a plate of metal or glass is placed in front and perpendicularly 

 or obliquely to the plane of projection; they are then collected in hot 

 water or any other non-inflammable liquid, or in any other manner, and 

 annealed or fired if need be, and achromatized in the manner hereafter to 

 be described ; there may be any number of openings o and also of blowers 

 that may be thought desirable. 



" The following are the processes for manufacturing the improved 

 lenses with concentric layers having variable refractive and dispersive 

 powers from the centre to the edges, and which process is applicable to 

 the manufacture of lenses of any form and dimensions, spherical, parabolic, 

 elliptical, and hyperbolic, concave, or convex. By means of the apparatus 

 represented at fig. 26 the form and thickness of the lenses from the centre 

 to the edge and their curves may be varied at pleasure according to the 

 degree of density or liquidity of the glass. This apparatus is composed, 

 first, of a hollow fixed foot carrying the bell-shaped vessel made of fire- 

 brick, and having openings for the pipes t, fi, into its interior for con- 

 ducting hydrogen or other gas and condensed air into the blow-pipe c, at 

 the orifice of which they are ignited ; second, of a shaft B, which may be 

 driven at a rapid speed by means of the pulley P in communication with 

 friction gearing ; it carries a capsule or cup g, made of platinum or fire- 

 clay. This cup may be either concave, as in fig. 26, or convex, or of any 

 other form, according to the form of lens required to be produced. A 

 drop or lump of liquid glass is to be placed upon the cup g, the apparatus 

 is set in motion, and when one layer has received the required form the 

 fire is moderated and the apparatus stopped, and the second layer of liquid 

 glass of the same or of diiferent density is laid thereon, and the operation 

 is continued as before, and so on until the lens has been brought to the 

 required form, thickness, and density. The various vitreous matters in 



