NATURAL PHILOSOPHY. 169 



rent colors of the spectrum being exhibited in the ruled spaces 

 -rding to the separations of the lines ; and in those cases where 

 tne distances between the lines are smaller than the lengths of the 

 violet light waves, no color is perceived : and it is stated that if in- 

 equalities amounting to '00002 line occur in some of the systems, stripes 

 of another color would appear in them. 



IMPROVEMENT IX THE MANUFACTURE OF LENSES. 



The following notice of an improvement in the manufacture of 

 lenses, is given in Newton's (London) Patent Journal : 



Tho dioptric lens, heretofore in use, for sea-lights, or other lights 

 requiring great intensity, being constructed of single zones or rings 

 made up of segments according to the diameter of the required lens, 

 has induced a belief that glass could not be prepared without incurring 

 the expense of grinding and polishing the curved surface, and that 

 economy dictated a method of manufacture embracing a center and 

 zones or segments. The inventor was induced to examine the method 

 of Ihe construction of the built-up lens, to try and reduce the expense 

 without diminishing the strength of the light, commencing with the 

 suggestions of Buffbn, that a spherical body, from its thickness, absorbs 

 light according to its density, and that a sectional figure of any required 

 shape and thickness could be cast of glass and ground in concentric 

 cones, to produce a lens, as partially accomplished by Abbe Rochon, 

 who prepared the way for the manufacture of the dioptric lens in se- 

 parate pieces by the ingenious Fresnel, termed " the annular band 

 lens," which is now used in our best light-houses. These lenses are 

 very expensive, for each separate piece must not only have its surfaces 

 formed with great accuracy, but all the separate pieces must be ar- 

 ranged to each other, so that when put together they shall form a per- 

 fect whole. This invention is to produce a dioptric lens which shall 

 present all the practical advantages of Fresnel's annular band lens, at 

 so cheap a rate as to admit of its being applied to all purposes requir- 

 ing intensity of light. The inventor makes dioptric lenses in one or 

 several pieces, moulded and pressed into the form required for the 

 surfaces ; and when made in several pieces, the required fit of the 

 several parts is produced by giving the reversed required form to 

 metal moulds in which the molten glass is to be run and pressed. To 

 promote focal intensity and prevent the absorption of light, each lens 

 is manufactured as thin as the size and number of concavities and 

 convexities will permit. 







CELLS FOR MICROSCOPIC OBJECTS. 



The following communication by Mr. L. S. Beale, is taken from the 

 Microscopic Journal, October, 1852. 



Some time ago a very simple method of perforating thin glass 

 occurred to me, which has been found to answer exceedingly well, 

 and it has this great advantage, that the microscopist can make cells 

 for himself of almost any dimensions required. 



