874 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
process. Where the object is entirely novel and the peculiar grain- 
like structure of the picture might cause erroneous conclusions, where 
there is a large amount of fine detail, or where, as in diatoms, the 
structure consists of a series of fine lines, or minute dots, elevations, 
or apertures, then this process is not so applicable. But even here it 
is serviceable if only the general appearance of the object is desired. 
One suggestion may be allowed to be offered — that in studying all 
process work the best effect is given if the picture is held at a rather 
greater distance from the eyes than the distance of normal vision, i. e. 
ten inches. By this means the attention of the observer will not be 
distracted by seeing the individual dots or points of which the image 
is made up, but he will still be enabled to appreciate all the delicate 
effects of light and shade. 
There are several methods in common use for producing what are 
called half-tone prints. The bitumen process, though commercially 
but little used on account of its slowness, is one of the best for re- 
producing detail, especially since Valenta has discovered some valuable 
improvements, while the numerous so-called enamel processes which 
have recently been introduced, modifications of the gelatin process, 
are valuable in that they are rapid and cheap. The cheapness, of 
course, is one of the strongest recommendations for the use of any half- 
tone process, as a cut which on wood might cost from 10 to 20 
dollars could be put into a half-tone for 3 to 5 dollars. Another 
advantage is that the amount of detail in a picture would make no 
difference in the price of a zinc plate, it being sold for a certain price 
per square inch, while the cost of a woodcut would depend very largely 
on the fineness of the detail which was to be reproduced. This kind 
of illustration has already been largely used in medical work, and the 
A. M. M. J. a year or two ago republished some half-tone cuts by the 
author of photomicrographs of sections of woods, showing the capabilities 
of the process. For the representation of very delicate work, the 
numerous photo-gelatin processes are more satisfactory, as the minutest 
detail can be accurately shown, but they are much more expensive, 
and must be printed on special paper and presses. But graphic illus- 
trations in some form add largely to the attractiveness of an article, as 
well as enabling the reader to comprehend at a glance the idea which 
is sought to be conveyed. Few can draw, but dry plates have made 
photomicrography almost a pastime, and the half-tone process offers, by 
all odds, the best mode of reproducing photographs with all the accuracy 
of the original, and with a minimum of expenditure of time and money, 
and it is to be hoped scientific periodicals will be led to make more 
use of this new method.” 
Drawing Photomicrographic Objects.* — Dr. H. G. Piffard has done 
much to simplify the drawing of photomicrographic objects, by means 
of his application of the prism to the Microscope. His method is to 
insert a right angle prism by means of a short tube in the place of 
the eye-piece of the Microscope, and on one of the square faces of the 
prism another short tube to hold the ocular. The object then having 
been placed upon the stage and focused, a piece of plain drawing- 
* Anthony’s Photographic Bulletin, xxiii. (1892) p. 516. 
