NATURAL PHILOSOPHY. 



IMPROVEMENT IX ELECTRICAL MACHINES. 



M. Provenzali, of Rome, has found that by covering a part of the 

 conductor of an ordinary electrical machine with a thin sheet of gutta 

 percha, the sparks that may be drawn from the part thus covered 

 greatly exceed in length, those which can be obtained from the part 

 uncovered. It appears that this effect depends upon the obstacle 

 which the insulating sheet offers to the dispersion of the electricity, 

 which dispersion tends to take place from the asperities of the surface 

 of the conductor, and which discharge in part at a distance this same 

 conductor, whenever it is approached with a non-insulated conductor 

 for drawing the sparks. M. Provenzali proposes to cover the whole 

 conductor of the machine in this way, to see if it will not protect it 

 from the action of moist air, and give always a considerable quantity 

 of electric fluid. In order to obtain the largest sparks, it is neces- 

 sary to have the insulating sheet strongly electrified. 



ELECTRO-CALORIC MACHINE. 



In 1844, M. Andrand put in action on the railroad from Paris to 

 Versailles, an air locomotive, in presence of a commission named 

 by Government. Although with some points of resemblance, it was 

 not precisely a caloric engine like that of Ericsson, against whom, M. 

 Andrand enters no claim of priority. The locomotive acted through 

 air at first compressed in a heater and then dilated by the heat. The 

 air acted at high pressure, and the generator consisted of a worm 

 plunged in a fire for the purpose ; on passing through this spiral tube, 

 the air was dilated ; then on reaching the water cylinders it under- 

 went additional dilatation, for the concave bottom of the cylinders 

 were furnished with plates of cast iron, which were at white heat. 

 The dilatation thus obtained, increased three fold, according to M. 

 Andrand, the power of the condensed air ; whence he concluded that 

 in order to arrive at a practical solution of the problem, the previous 

 compression could be dispensed with, and obtain at the same time the 

 condensation of the air by using for this purpose part of the expan- 



