ABSTRACT
A perfect microscopic object-glass is entirely useless when made to act upon parallel rays, like that of a telescope, the separate figures necessary to correct spherical aberration for each being as widely different from each other as an ellipse from a parabola. Care must be taken, however, in using the glasses, in such a solar microscope, that the illumination is directed truly through their axis, and likewise that they are placed considerably within the focus of the illuminator, otherwise the coloured portion of the sun’s image, formed by the prismatic edges of the illuminating glass. The swinish vulgar will always be gratified by such spectacles, because they have no idea that a microscope of any kind is to do more than exhibit objects very much dilated in point of bulk: if any optician could contrive an instrument, which would at one swoop take in the whole of a horse, ass, or elephant, and exhibit it.
