Intelligence and Miscellaneous Articles, 239 



This experiment seems sufficiently decisive. But the following is 

 far stronger. 



Experiment 2. — A plate was treated in all respects as in No. 1, 

 except that the application of the nitrate of mercury for removing 

 the developed image was made by yellow light. The plate, now 

 showing nothing but a uniform yellow film, was carefully washed, 

 and an iron developer, to which nitrate of silver and citric acid had 

 been added, was applied. In this way the original image was repro- 

 duced, and came out quite clearly with all its details. 



Now as every trace of a picture and all reduced silver had been 

 removed by the nitrate of mercury, it is by this experiment abso- 

 lutely demonstrated that the image is a purely physical one, and 

 that, after having served to produce one picture, that picture may be 

 dissolved off, and the same physical impression may be made to 

 produce a second picture by a simple application of a developing 

 agent. 



P.S. — Since the above was written, I have repeated the experi- 

 ment with a pyrogallic development, with similar results. Both the 

 first and second developments may be made with an iron developer, 

 or both with a pyrogallic. The experiment succeeds without the 

 least difficulty in either way.— Silliman's American Journal for July 

 1865. 



EXPERIMENTS ON THE PRODUCTION OF CYLINDERS OE ICE BY 

 PRESSURE THROUGH ORIFICES. BY M. FRESCA. 



These experiments were made by acting on ice contained in a cylin- 

 der 0'16 metre (about 6 inches) in diameter, with the requisite pres- 

 sure to drive it through a central orifice in its base 0*05 metre 

 (nearly 2 inches) in diameter. These plates, prepared by Tyndall's 

 method, in some cases coloured at the joints and in others not, 

 acted like plates of lead or of porcelain paste, as before explained by 

 the author to the Academy. The surfaces of the planes of division 

 or joints, originally flat, are transformed by the process, as with other 

 substances, into tubes concentric and perfectly distinct from one 

 another, thus indicating the movement of each point of the mass in 

 the course of the transformation. The cylinders of ice are longitu- 

 dinally furrowed ; and the furrows appeared to proceed from fractures 

 produced at the moment when a portion of the cylindrical block 

 leaves the orifice, and when, as a consequence, it ceases to be sub- 

 jected to pressure at the outer extremity. The porcelain paste 

 afforded the author delicate furrows or fractures of a similar kind, 

 and in some cases the material was divided into small separate 

 lamellae. The evenly-bedded structure of the cylinder of ice shows 

 that the origin of these fractures is subsequent to the first formation 

 of the cylinder. 



For a block of the dimensions employed in the experiments the 



