ON THE ITALIAN EXHIBITS. 197 



stand how these instruments register themselves. The wooden stopper 

 floating on mercury rises and falls with it, and transmits its motion to 

 this pendulum, which in its upper portion has an arc covered with 

 paper, on which at every hour, this needle, set in motion by clock- 

 work, makes a mark. This same needle advances a little after every 

 impression, and thus these marks form a curve upon the paper. 



I come now to speak of Nobili, and shall, for the sake of brevity, 

 mention only those objects which you see before you. Here is his 

 first astatic galvanometer, made in the year 1825. And this is 

 another instrument for hydro-electrical currents. Here is Nobili's 

 magnetoscope for proving the presence of the very slightest magnetic 

 influences ; it is composed, as you see, of a system of astatic needles 

 suspended to a thin thread of silk inside this crystal bell, surmounted 

 by a tube which has on its upper part a graduated circle, with an 

 index such as is used in scales " di torsione." 



Here are three different models of thermo-electrical piles. In the 

 construction of such instruments he attained great excellence. But I 

 want particularly to draw your attention to this one, which is com- 

 posed of thirty-six elements, bismuth antimony, and is provided 

 with a conical reflector ; it was of the greatest possible use to him in 

 the experiments which he carried on, partly in collaboration with the 

 celebrated Melloni, on the radiation of heat. All have heard of 

 Nobili's coloured rings, obtained by means of the chemical action of 

 the electric current ; this " rosettone" was obtained by him in this 

 wise. We have in Florence the complete chromatic scale constructed 

 by him, and who has read his memoirs on the subject knows with 

 what profundity he has treated this attractive argument. 



And, although I cannot put the instrument itself before your eyes, 

 allow me to remind you of his globe, round which there circulates an 

 electrical current for imitating the magnetical phenomena of the earth. 

 It was made by him in 1822, whilst it was only in 1824 that Dr. Birk- 

 beck presented a similar one to the Royal Institution (of London) ; 

 and, as he got his first idea from Barlow, it was henceforth known as 

 Barlow's Globe. 



With regard to the magneto-electrical machines of Nobili and 

 Antinori, and to their publications on the phenomena of induction, I 

 feel it my duty to add a few words. It is certain that your celebrated 



