WITH THE MICROSCOPE. 233 



The extreme detail, beauty of texture, and sharp delineation of the 

 objects in the prints from Mr. Delves' negatives marked a very im- 

 portant step. The frontispiece to this work was obtained by Dr. 

 Maddox in the following manner, as described in a note to me : 



" Prints selected from some of my negatives, representing objects 

 magnified in various degrees, varying from the i^ inch objective 

 to the yVth, were placed on a card in such a manner as to try to 

 balance each other in their effects, and such size of card adopted 

 that, when reduced one-half, it might correspond with the dimensions 

 chosen by yourself for the plate. The card of prints being placed 

 at the requisite distance, a Ross' 1 5-inch focus landscape lens was 

 used to obtain the negative copies. 



" To render the minutest line, especially in the Pleurosigrna 

 angulatum, well evident in the negative, it was necessary not to 

 carry the development or intensifying process too far, or these became 

 filled up and much obscured, hence the interspaces between the 

 figures allowed a little light to pass; as this seemed detrimental 

 and rendered the figures less effective in appearance, these parts 

 have been painted out. 



" The illustrations were photographed with the objective stated in 

 the ' explanation.' The T Vth objective was made by Mr. Wenham, 

 and through his liberality placed at my service." 



Many of these photographs require a magnifying glass to bring 

 out their detail. 



My friend Dr. Dean, of Boston, U.S., sent me some very perfect 

 photographs of sections of the medulla oblongata, taken with the 

 low powers. These are by far the most perfect photographic illus- 

 trations of structures from the higher animals that I have seen. 

 (" The Grey Substance of the Medulla Oblongata and Trapezium," by 

 John Dean, M.D., Smithsonian Contributions to Knowledge, 173. 

 Washington, 1864.) These photographs were also successfully 

 printed by photolithography. Dr. Duchenne, of Boulogne, also ob- 

 tained some very successful results with anatomical structures, and 

 M. Rouget has employed the same means in the ordinary way and 

 stereoscopically, to illustrate some of his views in minute struc- 

 ture. 



In 1865, Dr. A. Helwig, of Mayence, published his work on the 

 Crystalline Forms of Alkaloids, and their Sublimates, &c., illustrated 

 by a large number of photomicrographs. Dr. Moitessier has also 

 adorned his book on photomicrography, " La Photographic Appli- 

 quee aux Recherches Micrographiques, 1866," with three photograph 

 plates of various objects. 



Dr. Draper, of America, employed for many of the plates in his 



