148 ANNUAL OF SCIENTIFIC DISCOVERY. 



ington, from the published report of which the following sketch 

 was made. 



During the latter part of 1869, Col. Woodward began a series 

 of experiments with the design of removing certain difficulties in 

 the photographing of tissues on a large scale. The solar light 

 was used, and little difficulty was found in arranging a method 

 which gave most excellent results. Great annoyance was caused, 

 however, by the uncertaint} 7 of the weather, there being but few 

 days suitable for working to advantage. This led Col. W. to 

 seek some other means of illumination, and by the use of the 

 electric, magnesium, and lime lights he has succeeded in produc- 

 ing photo-micrographs with even the highest powers as well or 

 even much better than by ordinary sunlight. 



Two reports have been presented to the surgeon-general ; 

 the first dated January 4, 1870, concerning the use of the mag- 

 nesium and electric lights, the second, dated June 4, 1870, con- 

 cerning the use of the lime light. 



The electric light used in the first series of experiments was 

 produced by 50 small Grove's elements, using a Duboscq's 

 electric lamp. Not only could photographs be taken on as large 

 a scale as by sunlight, but the exaggeration of light and shadow 

 given by the electric light proved most admirably adapted to the 

 production of clear and well-defined photo-micrographs. The 

 magnesium light was found to possess many of the excellences 

 of the electric light, but its best effect is given when the object is 

 not magnified more than 1,000 diameters. 



With the electric light the following method was used in the 

 production of the photographs : 



The electric lamp was placed on a stool against the wall at one 

 end of the room, and its light concentrated by a pair of condens- 

 ing lenses on the lower lens of the achromatic condenser of 

 the microscope. The microscope, a large Powell and Lealand's 

 stand, was placed on a small table with levelling screws and ar- 

 rangements for raising and lowering it at pleasure. The lenses 

 employed were made by Wales, and specially constructed for 

 bringing the actinic rays to a focus. For powers above the 

 eighth-inch, the objectives of Powell and Lealand were found to 

 answer an excellent purpose. 



The electric light being arranged and working, the microscope 

 was moved till the centre of the achromatic condenser and the centre 

 of the illuminating pencil coincided ; the object was then placed on 

 the stage and adjusted. A cell of plate glass, filled with a satu- 

 rated solution of ammonio-sulphate of copper, was placed between 

 the light and the condenser, thus cutting off a large proportion of 

 the luminous and calorific rays, besides making the colors of the 

 object disappear, so that its appearance to the eye was the same 

 that its photograph would have when taken. 



The slide having been arranged, the eye-piece of the micro- 

 scope was removed, and the image allowed to iall on the ground 

 glass of the plate-holder, previously placed at the distance giving 

 the required magnifying power. The objective once carefully 

 focussed, the sensitive plate was exposed, thus finishing the diffi- 



