Lenses for Microscopes. 21 



ing the same,) the aberration of the diamond lens will only be 

 about -j^th of that produced by the glass one, even when their 

 thickness is the same ; but as the curvature of the diamond is 

 less, the thickness may be greatly diminished. 



The chromatic dispersion of the adamant being nearly as low 

 as that of water, its effects in small lenses can barely be appre- 

 ciated by the eye, even in the examination of that valuable class 

 of test objects, which require enormous angles of aperture to be 

 rendered visible, which it is evident must be of easier attainment 

 by diamond magnifiers than by any other sort of microscope. 



A mathematical investigation of the spherical aberration of 

 the diamond when formed into lenses, I hope to lay before the 

 public at a future opportunity. The comparative numbers 

 here taken from the longitudinal aberration are, I believe, 

 sufficiently accurate for practical purposes. 



18, Picket' Street i Strand, 



Analysis of a newly -discovered Spring, at Stanley, near 

 Wakefield,^-By Mr. William West. 



Mineral springs, dependent for their characteristic properties 

 on carbonate of soda, appear to have been little noticed by 

 chemists, and to have been still less attended to as curative 

 means ; at least in proportion to the multitude of cases in which 

 that substance is administered in various other forms. Indeed 

 the inference to be drawn from the silence respecting the 

 modes of analysis adapted to such waters in our best elementary 

 treatises, is that they have hitherto been very seldom met with. 

 In one district, however, of Yorkshire, carbonate of soda is of 

 frequent occurrence ; it is found in the ordinary springs ; often 

 at the same time with substances with which, in artificial solu- 

 tions, or when concentrated, it. would be considered wholly 

 incompatible ; while at other times it is the predominant, or 

 the only remarkable saline constituent. An analysis of a water 

 of this kind, known by the name of the Holbeck Spa, has 

 lately been published in the Annals of Philosophy, by my friend 

 E. S. George; similar springs are found, I understand, as far^ 



