894 SEC. 20. COLLECTION OF APPARATUS AND PHOTOGRAPHS 



first the foundations of the chemical theory of the pile. (See Description of 

 a new electrometer and some experiments in charging the voltaic column, 

 by Ab. Dal Negro, T. X. I., Italian Society of Science, Modena, 1804.) 



(5.) 1 and 2. OLIGOCHRONOMETER, by Prof. Salvatore Dal Negro, 

 applied to researches on the laws of weights falling freely. By 

 cutting the thread which holds the weights suspended, the 

 pendulum is set at liberty, which, being stopped by the weight 

 arriving at the end of its course, cuts another thread. 



3. Oligochronometer. (See New method for measuring the 

 smallest fractions of time, invented by the Ab. Dal Negro, Padova, 

 1816. New Oligochronometer, Padova, 1809.) 



(6.) MODEL OF OLIGOCRONOMETER, by Dal Negro, applied to 

 the measurement of the velocity of projectiles. 1 . Cannon, the ball 

 of which on coming out of the mouth breaks a thread which sets 

 the pendulum of the Oligochronometer in motion (2). 3. Movable 

 hinged target, which on being hit breaks a thread which stops the 

 pendulum. 4. Details of the Oligochronometer. (See New 

 method for measuring the velocity of projectiles, 1824, by Sig. Ab. 

 Dal Negro, Padova, 1824.) 



(7.) 1. ELECTRO-MAGNETIC MOTOR, by Prot\ Salvatore Dal 

 Negro. Two permanent magnets suspended like a pendulum 

 can oscillate in the proximity of the poles of a temporary magnet, 

 in which the current circulates alternately in contrary direc- 

 tions, by means of a swinging commutator with small cups of 

 mercury moved by the pendulum itself. The attractions and 

 repulsions which result render the movement of the pendulum 

 continuous, and this, by means of levers, is transformed into 

 continuous rotatory motion. (See Description of electro-magnetic 

 rams (arieti), both simple and compound, by Prof. Ab. Dal Negro. 

 Padova, 1838. Also Annali delle Scienze del Regno Lombardo- 

 Veneto, tomo III. bimestre I., 1838.) 



2. Electro-magnetic Pendulum, by Prof. Dal Negro. The rod 

 of the pendulum is formed by a bundle of permanent magnets, 

 one extremity of which can oscillate between the poles of an 

 electro-magnet. The inversion of" the current is effected as in 

 the above-described motor. This pendulum is interesting, his- 

 torically, as recording the first attempts at using electricity as a 

 motive power. 



(8.) ELECTRO-MAGNETIC MOTOR, by Prof. Dal Negro. The 

 apparatus consists of a lever of the first order, to one extremity 

 of which is attached the anchor of an electro-magnet, and to the 

 other a hammer which by alternate elevations and descents strikes 

 a rod. and produces a movement like that of a shuttlecock, and 

 afterwards the lifting of a weight. This movement of the lever 



