IK) Dr. Goring on the neio Microscopes, Sj^c. 



so closely to the side of the tube containing the metals, as to 

 prevent the artificial illumination from being thrown down 

 upon opaque objects, so as to be returned at a sharp angle, 

 Unless we employ silver cups, with which they are a match 

 for any object requiring this sort of light, such as the fly's foot, 

 &c. All those opaque objects which require an oblique radi- 

 ance, such as the whole family of lines, are shown decidedly 

 better by the reflectors than the refractors. The 0.3 focus 

 metals with 0.2 aperture, allow just room enough for this kind 

 of illumination, and exhibit this class of bodies in a style which 

 no glass microscope will, I think, ever be able to surpass or 

 even equal. In short, where is the object which a good Amician 

 Cannot show in the best possible manner?* it has, however, 

 one imperfection, which renders it a disagreeable instrument for 

 giving a general view of objects, viz. it will not give a very low 

 power without a contracted field of view, with a nebulosity in 

 the middle of it ; whereas the achromaiics are not subject to 

 any such inconvenience : the superiority, therefore, with very 

 low poivers, must be conceded to them. Both of these valuable 

 instruments have their separate utilities and applications, and 

 I think it may be asserted, without disparagement to either, 

 that each possesses the properties which the other is deficient 

 in. Those who have not seen transparent objects wdth a good 

 reflector, cannot well form an idea of the effect produced by the 

 total absence of all coloured fringes, more especially, perhaps, 

 on very delicate animalcula3. In the best achromatics there is 

 always a tinge of colour left by the secondary spectrum, (though 

 I must say that my 0.2 object-glass approaches very nearly 

 to the perfection of a reflector in this point.) If, in addition to 

 the total absence of chromatic dispersion, a perfect figure has 

 been given to the metals caused to correct along with truly 

 achromatic eye-pieces, upon the same principle that the hy- 

 perbolical aberration of the large metal in a Gregorian telescope 

 is made to counteract the spherical error of the small one, 



♦ In Vol. i., No. 11, of Gj7/'# Techno/ogtca/ Repository, August 1827, Art. 22, "Oa 

 Jt difficult test object for the IMicrnscope," is contained an underhand insinuation, 

 calculated to prodme an inopression to the mind of the reader, that the Amician mi- 

 croscope will not sliow the minute hairs on the larva of a dern.estes. I must state 

 that the said hairs are scarcely worthy to be called test objects, being far more easy 

 than bat's hairs, and demonstrable by any microscope; t/ie two inch metals of the 

 Amician show Uiem perfectly well. 



