Prof. Gonnella on a new system of Eye-pieces. 71 



induction is developed in the metallic thread, the circuit of which is 

 closed an instant after the voltaic circuit has been shut or opened. 

 He believes, that by following up these experiments he shall be able 

 to connect the principle of electro-dynamic induction with that of 

 the influence of the electricitj' of tension. 



M. Matteucci mentioned his experiments on the current yielded 

 by the frog, and described some new experiments on the torpedo. 



M. Carlini spoke of the use of the barometer in the measurement 

 of heights, and described an apparatus for the purpose of having the 

 level of the mercury constant. 



M. Marianini read the history of two cases of paralysis which were 

 completely cured by the use of dynamic electricitj', applied in an in- 

 termittent manner. 



M. Zantedeschi confirmed the experiments of M. Matteucci on 

 the torpedo ; he thinks that the nerves come from the dilatation of 

 the medulla oblongata, which forms the fourth lobe, with the gray 

 matter which covers it. — M. Savi has also made the observations. 



M. Morren has found phosphorus in glow-worms, as well as a 

 system of prisms or transparent lenses above the luminous matter. 



Professor Gonnella* presented some printed memoirs, in one of 

 which appears the theory and the description of a machine for measu- 

 ring plane surfaces, which he had invented and constructed in 1824, 

 and an abridged memoir of which he had published in the Antologia 

 for 1825. In another of these memoirs he gives a theory of new 

 systems of eye-pieces of arbitrary lengths for the Newtonian tele- 

 scope, and for spherical as well as for parabolic object-glasses, ac- 

 cording as is best suited for artists. In reducing for each telescope 

 the length of the tubes of the eye-pieces greater than the semi- 

 diameter of the object-glass, we may substitute for the small plane 

 metallic mirror a rectangular prism of glass, very small, whatever 

 may be the opening of the object-glass, since the prism may be 

 placed very near the focus without the eye of the observer being 

 obliged to be within the great tube ; for the length of the eye-piece 

 determines the place of the eye on the outside of this same tube. 

 We thus obtain the power of constructing the best telescopes, with 

 the prism, as pointed out by Newton, of large dimensions ; for, the 

 prism being very small, we may, — 1st, easily find pieces of perfect 

 glass for them ; 2nd, we may have the total reflexion of the rays, 

 since tbe quantity of liglit absorbed by the thickness of the prism is 

 insensible ; 3rd, we may obtain the advantage that the loss of the 

 central rays of the object-glass, intercepted by the prism, shall be 

 very small in relation to the diameter of the object-glass, and always 

 emaller relative to the greatest diameters ; for the size of the prism 

 is always constant for all the object-glasses, viz. about an inch for 

 each side of the right angle of the rectangular triangle which forms 

 its base. In short, it only remains for us to observe, that the tele- 

 scopes with the prism have double the clearness of those which have 

 the small plane metallic mirror. 



* [This notice is extracted from a letter addressed by Prof. Gonnella to 

 Mr. Babbage, and kindly communicated to us by that gentleman. — Edit.] 



