Mr. H. Hennessy on an Application of Photography. 273 



appeared entirely on agitating its solution with a great excess 

 of animal charcoal. 



By analogical reasoning I was led to try the effect of this 

 agent on salts of inorganic constituents, and here a similar ac- 

 tion was exerted. A large quantity of sulphate of magnesia 

 was removed from its solution in water, as also of chloride 

 of barium, sulphate of soda and other salts. The fact of sul- 

 phate of lime being removed from its solution has I find been 

 already noticed by Payen and Graham. 



On laying the preceding experiments before the Society, I 

 stated that I proposed to carry on the investigation, but I 

 have since met with a paper by M. Chevallier*, " On the ac- 

 tion of Animal Charcoal on Metallic Salts," in which he also 

 proposes investigating its action on the organic salts. Had I 

 been aware of the existence of this paper at the time, I cer- 

 tainly should not have brought my own experiments forward, 

 and shall not continue the investigation until M. Chevallier 

 has closed his researches. I can only express my regret that 

 I should even thus far have anticipated his results. 



XLI. On the Application of Photography to Registering the 

 Thermometer and Barometer. By Henry Hennessy f. 



THE delicacy required in an instrument for registering 

 continuously the indications of the thermometer or ba- 

 rometer is such that contrivances of a merely mechanical na- 

 ture could never fulfil such a purpose. As I am not aware 

 that the photographic process has been ever applied to effect 

 this desirable object, I here present some account of my at- 

 tempts at showing the practicability of such an application of 

 that process :f. It occurred to me a few months since, that the 

 shadow of the mercury, or whatever fluid may be used to in- 

 dicate by its oscillations physical changes going on in the at- 

 mosphere, could be received upon a sheet of prepared photo- 

 graphic paper or a Daguerreotype plate. In proceeding to 

 make the necessary experiments, I found that the common 

 mercurial thermometer was not adapted for my purpose. No 

 method in my power could prevent the light from travelling 

 as it were around the column of mercury, and thus preventing 

 the formation of a distinct shadow. It appears that the best 

 method for obviating such an inconvenience would be to have 

 the sides of the thermometer tube made of some opake sub- 



* Comples Rendiis, vol. xix. p. 1279. f Communicated by the Author. 



X [We are informed by Mr. Hunt, that many years since, Mr. Thomas 

 Jordan tried a great many experiments on using photographic papers to 

 register meteorological instruments, and published his results in the Reports 

 of" the Polytechnic Society. — Ed.] 



Phil. Mag. S. 3. Vol. 27. No. 180. October 1845. T 



