155 



SECTION 5. MOLECULAR PHYSICS. 



WEST GALLERY, UPPER FLOOR ROOM Q 



I. SPECIAL COLLECTIONS. 



Hydrostamm (Hydrometer), with ballast of mercury, for 

 liquids lighter than water. The Accademia del Cimento. 



Hydrostamm (Hydrometer), with ballast of shots, for 

 liquids heavier than water. The Accademia del Cimento. 



The Hydrometer, No. 20, was probably used for determining the specific 

 gravity of precious stones ; by observing to what degree it was immersed 

 without the precious stone, and with the precious stone placed upon the little 

 metallic disc, suspended by the three little chains. This is also a fitting place 

 to draw attention to the so-called " Palla d' Oncia " (ounce ball), of the 

 Grand Duke Ferdinand, u glass globe which displaces very nearly an ounce 

 of water. On the stem several rings were placed in order to make it sink, 

 and then by the number of these rings, it was known what the specific gravity 

 of the liquid was into which it had been immersed. 



Besides the Hydrometer, No. 21, for determining simultaneously the tem- 

 perature and the corresponding specific gravity, other ones of the Accademia 

 del Cimento, which are true thermometers, having in addition the scale of 

 graduation of hydrometers. 



Hydrostamn (Hydrometer), with a small metallic balance, 

 the first idea of Nicholson's areometer. 



The Accademia del Cimento. 



Photograph of the Hydrostamm (Hydrometer), enclosing 

 a thermometer. The Accademia del Cimento. 



Ball of Metal, filled with water, and prepared by the Accade- 

 mia del Cimento to serve in the experiments for the compression 

 of water. The Accademia del Cimento. 



Ball of Metal, still containing some water that served for the 

 experiments of the Accademia del Cimento on the compression 

 of water. The Accademia del Cimento. 



Among the many experiments made by the Accademia del Cimento for 

 the compression of water, either Jby means of rarefied air, by the pressure of 

 mercury, or by the force of percussion, the last one which was carried out 

 with a ball of very thin silver, has attracted the most universal attention. 

 When beaten with a hammer, the water " sweated through all the pores of the 

 " metal, like quicksilver spouting through some skin in which it was being 

 " squeezed." 



