SCIENTIFIC CONGRESS OF CARLSRUHE. , 365 



tuning-fork, suspended above a glass balloon containing a quantity of 

 water determined by experiment, a distinct sound, capable of being 

 heard throughout the hall of audience. The balloon must not be full, 

 nor ought the fork to touch it ; the instrument is simply held with the 

 hand and in the prolongation of the neck of the balloon. The sound 

 emitted depends on the position of the two branches of steel in reference 

 to the neck of the balloon, the perception of the sound being very dis- 

 tinct when the plane of these two branches is in the axis of the neck, 

 but none at all when the plane is perpendicular to it. 



These facts had been recognized by M. Dove while engaged in re- 

 searches to ascertain- whether the ear which receives during a certain 

 space of time some determinate sound becomes insensible to that sound, 

 as the eye which has been fixed for some time on a certain color be- 

 comes insensible to that color. It might be said that the eye becomes 

 habituated to the color, as the sense of smell becomes habituated to 

 certain odors. 



The analogy which exists between acoustic vibrations and those of 

 light is borne out in this respect, inasmuch as M. Dove has satisfied 

 himself that the ear may in effect be habituated to a sound to the extent 

 of no longer perceiving it, after having been subjected to the impression 

 for a time more or less protracted. 



Iron in a state of great comminution, as we obtain it, where one of 

 its oxyds is reduced by hydrogen, has for sometime been employed in 

 medicine. Well prepared, this reduced iron is so oxydizable that it 

 kindles spontaneously in the air and burns with vivid sparks. Now, 

 there has lately been established in the Tyrol a factory in which iron 

 in powder is produced, having a considerable degree of tenuity, although 

 the pulverization is effected mechanically and, as it would seem, with 

 very delicate files. Experience has not yet pronounced with respect 

 to the therapeutic properties of this product; neither does it burn spon- 

 taneously in the air, although it is extremely combustible, as was proved 

 by an experiment which M. Magnus exhibited in the presence of the 

 meeting. When a flame is applied to these filings they do not kindle; 

 but they burn readily when previously suspended to the poles of a 

 magnet. The experiment, which is quite a pleasing one, is easily con- 

 ducted: there needs but to plunge the magnet into these filings, when 

 they group themselves around the poles and remain suspended, forming 

 a sort of beard, to which, if a match is applied, combustion immediately 

 takes place and progresses rapidly. If we then shake the magnet, a 

 multitude of sparks will be detached, being the particles of the iron in 

 a state of combustion. 



This property seems to pertain exclusively to these filings from the 

 Tyrol, for I have ascertained that iron recently reduced possesses it in 

 a very slight degree, and that the same iron, after having been pre- 

 pared for some time, will have entirely lost its pyrophoric quality. 



At Frankfort-on-the-Main there exists a species of scientific associa- 

 tion, the Pliysikalisclie Verein, composed in great part of men of the 

 world, who meet twice a week, for the purpose of keeping themselves 

 abreast of the progress of physics and chemistry. The expenses of the 

 association are provided for by an annual assessment of ten florins on 

 each member. Science is here expounded by M. Boettger, than whom 



