12 Maddox^ on the Delineation of Microscopic Objects, 
reflected lights to which may be added polarized and artificial 
illumination and the employment of coloured media. 
Finding how much the appearance of an object may be 
altered by the direction of the illuminating pencils^ as will be 
recognised in some of the photographs of the Coscinodiscus_, 
&c.^ where the focus remained unaltered, the plan of deter- 
mining the constant focus for a certain objective and object 
has been seldom attended to, but in most cases trials 
have been repeated until the appearance of the negative 
seemed satisfactory, due regard being made for the common 
over- correction^ ^ where necessary. As the objects are 
focussed in sunlight, it must be remembered there is a 
chance, without some care, of softening the cementing medium 
of the lenses of the object-glasses or of ^^firing^^ the object. 
The advantage of the prism was noticed more than three years 
since, and consists in the readiness with which the centring 
of the object-glass and condenser can be recognised on its 
surface, and a trifling alteration given to the course of the 
rays entering them. 
A few stereophotographs have been taken by the plan sug- 
gested by Professor Wheatstone, also by the method pro- 
posed by Mr. Smith ; the best negative was fractured by a 
fall, but its definition was barely satisfactory. That of the 
animal (parasite ?) found on the Brittle Star was by the 
plan of masking the alternate half of the front lens of the 
objective, as also of the Brittle Star, seen by transmitted light. 
The print of the former appears rough, as the object was 
mounted without other preparation than gentle washing, its 
edges being covered by Diatomacese. No particular scale 
has been adopted as regards the magnitude of the image, it 
being generally preferred to render the object about the size 
usually chosen by microscopists ; still many of the negatives 
will bear considerable amplification, if required. 
However inadequately this subject is now placed before 
you, it possesses in itself a sufi^icient charm and interest to 
claim your attention to the extended variety of a ^'^ beau- 
teous garniture'^ that can be made to unfold its exquisite 
tracery by the simple means advocated, enable us ^' to imitate, 
in some faint degree, and to admire, at least, where we cannot 
imitate, the perfection^^ that adorns even Creation^s lowliest 
forms. 
