440 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



will break the contact ; gravity will spread the globule out 

 ao-ain, when it will asrain touch the iron and contract ; and 

 so on. The explanation of this phenomenon is to be found 

 in the fact that the electric current developed on contact of 

 the two metals changes the capillary constant of the mer- 

 cury, and hence its form. This is the action which M. Lipp- 

 mann has utilized in his motor. In a glass tank filled with 

 diluted sulphuric acid are two small cylinders containing 

 mercury. A bundle of capillary tubes, open at both ends, is 

 placed in each cylinder, resting on the mercury, each bundle 

 being: connected above with one end of a walkingj-beam, to 

 the prolongation of which is attached a connecting rod, 

 crank, and fly-wheel. By means of a commutator on the 

 axis of the fly-wheel, the mercury in each cylinder is alter- 

 nately connected with a small battery ; its capillary constant 

 is changed, its ascent in the tubes increased, that side pre- 

 ponderates, and causes a semi-rotation of the fly-wlieel. This 

 sends the current to the other cylinder, which, acting simi- 

 larly, completes the rotation. As many as one hundred rev- 

 olutions per minute have been obtained with this engine. 

 Conversely, on rotating the fly-wheel by hand, a galvanom- 

 eter in the current indicates the production of an electric 

 current. 3 -Z?, XXXV., 5. 



EAILWAY SIGNALS AND BLOCKS. 



The Highland Railway of Scotland has introduced upon its 

 road what the English journals describe as a novel and in- 

 frenious combined block and si2;nal svstem, the invention of 

 Dr. Whyte, who has devoted several years to the w^ork of 

 improving the mechanical arrangements for operating rail- 

 way trains. The system is entirely self-acting, and its opera- 

 tions are performed with the agency of an electro-magnetic 

 machine of simple construction. An engine running past, 

 say two stations, blocks the line at the first by raising a 

 semaphore ; places an automatic check against the passing 

 of a second engine by the ringing of an alarm-bell on the 

 second engine itself, should it attempt to follow; announces 

 its approach to the second station, or can be stopped by the 

 station-master there ; Avhile on reaching that station it clears 

 the line at the previous one of both semaphore and alarm- 

 bell, so as to leave it free for any approaching train. The 



