596 
Transactions of the Society. 
important features of the plant structure are often destroyed. It will 
therefore be readily seen that if I cut a section of one of the calcareous 
nodules containing our coal plants, and cut the section say I /8 in. 
thick (which is not too thick considering the nodules are calcareous), 
polishing both sides and fixing one side to a glass slip as I shall show 
you, I can grind down the section slowly ; and at various stages, by 
my plan of photographing opaque objects, I can get at least six photo- 
graphs, each perhaps exhibiting features different to the rest, besides 
leaving me a transparent section for microscopic examination. It will 
thus be seen that these coal plants can be more fully studied by this 
plan, even from very fragmentary material, which is often the 
condition in which many of the coal plants are found. 
Of my camera I need to say very little ; its construction will be 
readily understood from the appended plate (plate XIV.). It has 
been built up piecemeal, but has absorbed much of my leisure for 
several years. I can use a range of powers from a 5-in. rectilinear 
lens down to my 1-in. microscopic objective for opaque photography, 
and in photographing transparent objects I can use my microscopic 
objectives from 4 in. down to a 1/16. The view (plate XV.) shows 
the light as transmitted to an opaque object when the argand or 
incandescent burner (which I now use) is raised to its proper height, 
and when the burner and condenser are lowered to throw the light 
direct through the object ; it is then fixed for transparencies. 
I thought it might be necessary to bring a few lantern slides and 
a few slides of sections in various stages of preparation to further 
illustrate our subject, and if any gentleman would like to ask any 
question on the slides or the camera I shall be most pleased to give 
further information. 
P.S. — I may just add that the stage or object-holder to the 
camera is so constructed at the back as to receive or hold all the 
substage appliances that I have for my large Microscope, which I 
have often used as occasion has required.* 
* I ought, to have made the remark in my paper that in preparing sections of our 
coal plants each plane or surface intended to be photographed ought to be first 
ground to a smooth surface and then flooded with a few drops of dilute hydrochloric 
acid (1 part in 6 parts water), and when the effervescence ceases wash and dry the 
section, which is then ready to expose in the camera. This procedure is essential to 
show up the structure with the boldness that is shown by the view (plate XV.). 
