236 SEO. 8. HEAT. 



The mechanical principle of its construction is as follows : The receiver in 

 which the rotation takes place is in fact the extended vacuum of a barometer. 

 Through the mercury of this barometer a shaft communicates a slow motion 

 to some machinery in the receiver. The velocity of this motion is there 

 greatly increased by means of a suitable train of wheels, until at length a 

 vertical disc is made to rotate with great rapidity on a horizontal axis. If 

 this disc be made to rotate in an ordinary obtainable vacuum it will become 

 heated, and the question is to determine whether this heating of the disc is 

 entirely due to the friction of the residual air, or to something else. 



Two wires, covered with gutta percha, carried through the bed-plate of the 

 apparatus, convey into the receiver a thermo-pile arrangement, by means of 

 which the temperature of the disc may be measured. This thermo-pile may 

 either measure the increased temperature of the disc after rotation by radia- 

 tion in -which case it is fitted with a reflecting cone ; or it may be made to tap 

 the surface of the disc after rotation in which case there is an arrangement 

 working through a barometric tube, by means of which the pile may be 

 brought up to the disc in vacuo after rotation. Finally, there is an arrange- 

 ment, working also through a barometric tube, by means of which a vessel 

 containing some peculiar chemical substance may be uncovered in vacuo at 

 will. The object of this is to reduce the pressure of the vacuum by chemical 

 means. For instance, if we have a carbonic acid vacuum made as low as it 

 can be made by ordinary means, a vessel containing moist potash Avould be 

 uncovered, and a great part of the residual gas absorbed. The experimenters 

 by this means have obtained a vacuum as low as 0'025 in. The conclusion 

 from these experiments appeal's to be, that there is a certain heating of the 

 disc which does not depend on the residual air. 



lO97a. Diagram representing the Apparatus of M. Reg- 

 nault, by M. d'Obelliane. Polytechnic School, Paris. 



1097b. Apparatus, by M. Dulong and Petit, for measuring 

 the Dilatation of Mercury with overflow thermometer. 



Polytechnic School, Paris. 



1O98. Effects of Heat on Nature. 9 Senarmont crystals 

 for heat. Laurent. 



1100. Automatic Fire Extinguisher and Alarm. For 



ships, factories, and all places where steam apparatus is employed. 



Sanderson fy Proctor. 



The action of the apparatus is as follows : 



Thermometers are fixed on the ceiling or elsewhere in the room, and arc 

 set to complete an electric circuit at a given degree of heat, each thermo- 

 ter being in connexion with a galvanic battery and electro-magnet. A steam 

 valve is also fixed in the room, communicating with the valve at the boiler. 

 As soon as a fire breaks out, and raises the temperature of the nearest ther- 

 mometer to the given degree, the electric current is complete, and the electro- 

 magnet, by a very simple contrivance, opens the steam valve in the room and 

 the valve at the boiler, the steam rushes into the room at the existing pressure 

 of the boiler, envelops the flame, and, by well-known chemical laws, effec- 

 tually extinguishes the fire. Simultaneously with the action of the electro- 



