1030 Transactions of the Ameeican Institute. 



film. He had found that the solution -worked most satisfactorily 

 after having been prepared a considerable time, though he had 

 produced good results with new solutions by adding a small quan- 

 tity of tannic acid. 



Prof. Joy exhibited specimens of Mr. Woodbury's photo-relief 

 printing from metal plates, and explained the workings of the pro- 

 cess as detailed to him by the inventor. He also exhibited the 

 mitrex or photographic image in a gelatine film from which the 

 metal plates were formed; also, several plaster casts from photo- 

 graphic impressions of microsopic objects. Prof. Joy also exhib- 

 ited several photographic impressions in natural colors upon metal 

 plates, by Niepes St. Victor, and gave some of the details of the 

 process by which they were produced. A very thin film of silver 

 was formed upon the plate, which was alternately exposed to the 

 action of light in the camera, and to heat sufficient to raise its tem- 

 perature to near the fusing point. 



Mr. Anthony thought that the great obstacle in the successful 

 working of Mr. Woodbury's process was the tendency to lateral 

 spreading of the actinic action in the gelatine film, which rendered 

 it very difficult to produce sharp definitions of fine lines and points 

 in copies by it. 



Mr. Dixon stated that all pictures produced in the solar camera 

 must of necessity lack much in definition, from the fact that every 

 ray of light passing into such instruments was so refracted as to 

 preclude the possibility of obtaining a perfect image. 



Mr. Chapman had found that far better results were produced 

 by interposing a ground glass between the condenser and negative, 

 than by allowing the unobstructed light to pass directly through 

 the negative. 



Mr. Boyle believed that a solar camera might be so constructed 

 as to give far better results than are obtained by those now used. 



The Section then adjourned to the fii'st Tuesday in February. 



February 4, 1868. 

 Prof. Jot in the chair; John IIollenbeck, Secretary pro tem. 



Minutes of the last meeting were read and approved. 

 Prof. Joy presented a communication, with a print, from Dr. H. 

 Carrington Botten. The communication was as follows: 



