62 report — 1859. 



On a Changing Diaphragm for Double Achromatic Combinations. 

 By A. Claudet, F.R.S. 



Mr. Claudet explained the construction of his contrivance, intended to reduce or 

 increase the aperture of a double achromatic lens without having to unscrew one of 

 the lenses and without any slit on the tube. This is done by two rings revolving on 

 one another, like the top and bottom parts of a round snuff-box, and each carrying 

 a number of india-rubber stripes, the other end of which was attached on the opposite 

 ring ; so that making the ring not fixed in the tube to revolve by an external pinion, 

 the india-rubber stripes were drawn intermixing each other, gradually reducing the 

 aperture until each of them was extending on the diameter of the tube, on which 

 disposition the whole aperture was shut. Mr. Claudet exhibited also the very in- 

 genious pupil diaphragm, invented by Mr. Maugey, optician in Paris. 



On an Instrument for exhibiting the Motions of Saturn's Rings. 

 By Professor J. Clerk Maxwell. 

 The author exhibited an instrument made by Messrs. Smith and Rarnage of Aber- 

 deen, to exhibit the motion of a ring of satellites about a central body, as investi- 

 gated in his ' Essay on the Motion of Saturn's Ring.' It is there shown that a solid 

 or fluid ring will be broken up, and that the fragments will continue in the form of a 

 ring if certain conditions are fulfilled. The instrument exhibits the motion of these 

 fragments as deduced from the mathematical theory. 



On a New Photometer. By the Abbe Moigno. 



The Abbe said that the instrument could be applied to determine the intensity of 

 the light of the fixed stars, and even of the several parts of the surface of the sun. 



On a New Electro-Medical Apparatus. By M. Ruhmkorff, exhibited and 

 explained by the Abbe Moigno. 

 The Abbe briefly described Daniel's, and Grove's and Bunsen's galvanic batteries, 

 the chief objection to the two latter being the evolution of nitrous acid fumes. The 

 peculiarity of the instrument he exhibited was, that sulphate of mercury in solution 

 contained in two neat little cups of carbon was used to excite the zinc ; a small bat- 

 tery of two cells, aided by a Ruhmkorff's coil, packed up in a small box, constituted 

 the apparatus. 



On Becquerel's Phosphoroscope. By the Abbe Moigno. 



On the Phonautograph, an Instrument for registering Simple and Compound 

 Somids. By the Abbe Moigno. 

 The Phonautograph is an instrument which consists of a large chamber or drum, 

 of a spheroidal form, with a diaphragm or drum-head at one end, which, by a 

 system of levers, works a pen to record the sounds which the form of the cham- 

 ber causes it to concentrate on the tympanum. The Abbe exhibited a drawing 

 to the Section, which explained the construction of the instrument, and then ex- 

 hibited drawings showing the actual markings of the pen over a sheet of paper car- 

 ried past it by clockwork ; — 1st, when tuning-forks sounding various notes were 

 vibrated in presence of the instrument ; 2nd, when several notes were sounded on a 

 diapason pipe; and 3rd, when a person spoke before it. In the first two cases, the 

 recording pen drew such regular curves, that the number of vibrations corresponding 

 to the note as seconds could be counted, and, as the Astronomer Royal observed, 

 they were obviously the curve of sines. In the case of the human voice, the words 

 spoken were written below the corresponding tracings of the pen ; and although 

 these were very irregular, yet a marked correspondence could be traced, especially 

 where the words contained r, g, and other well-marked low or guttural sounds. 



Portable Apparatus for Analysing Light. By M. Porro. 

 This instrument was a telescope, at the side of which the light to be analysed 



