ILLUSTRATING ITALIAN SCIENCE. 895 



produces the inversion of the current in the electro-magnet, and 

 by means of a swing commutator with small cups of mercury. 

 (See Description by Prof. Dal Negro, Padova, 1838, and in 

 Annali delle Scienze del Regno Lombardo-Veneto, tomo VIII. 

 bimestre 1, 1838.) 



(9.) 1. MACHINE for DIVIDING. (Salleron, Paris, 1870.) 



2. Cathetometer of the Tecnomanasio of Milan, improved in the 

 workshop of the Astronomical Observatory at Padua ; added to it 

 is an internal counterpoise. 



3. Balance of precision, by Deleuil, of Paris. 



4. Quadrant Areometer, by Poleastro (1803). It is a hydro- 

 static balance with quadrant. It is used to ascertain the density of 

 fluids, and is much more correct than ordinary areometers. 



5. Sphaerometer, by B runner (1870). 



6. Goniometer, by Babinet. 



(10.) 1. MODEL of a PUMP by suction and. 



2. Barometer, by Poleni (1740-1760).* ff^ 



3. Barometer, by Amontons. 



4. Barometer, by Cassini. V^* & Si 7* 



5. Barometer (quadrant). \v?^v^ 7" O< ** 



6. Barometer of Fortin. 



7. Barometer of Fortin, constructed by Bellani. 



8. Syphon barometer, constructed by Bellani. 



(11.) 1. AIR-PUMP by suction and pressure, by Deleuil. Gives 

 rarefaction to 2 mill., and compression to 10 atmospheres. The 

 effect is double, and the piston does not touch the walls. 



2. Differential manometer of Regnault. 



3. Metallic manometer. 



(12.) 1. DOUBLE SIREN of Helmholtz (Koenig, Paris). 



2. Apparatus by Koenig for the combination of vibrating forces. 

 May also be used for the experiments of Lissajous. 



3. Apparatus by Koanig for the interference of sounds. 



4. Organ pipes with manometrical capsules, by Koenig. 



5. Apparatus for musical flames. 



6. Analyser of sounds (Koenig). 



7. Acoustic interrupter. 



(13.) 1. HELIOSTAT, made at Padua in 1828 by the younger 

 Tessarolo, resembling, with modifications, that by Prandi. The 

 reflected ray may be thrown in any direction. (See Opere Scient. 

 di Bologna, 1824, p. 244, and Santini, Struinenti Ottici, vol. 1, 

 Padova, 1828.) 



2. Heliostat of Silbermann ; made at Paris. 



* A constant level in the vessel is obtained by the immersion of a screw. 



