84 SEC. 3. MEASUREMENT. 



the cement block breaks, prevents the lever from falling more than half an 

 inch. 



These machines are now in general use, nearly one hundred of them having 

 been sent to different parts of the world. They are principal!}' used by the 

 leading royal and civil engineers in this country, and by a large number of 

 contractors and cement manufacturers. 



42 Ob. Drawings of Machines and Apparatus for testing 

 Materials. Charles Jenny, Vienna. 



Five* sheets of drawings, representing : 



1. Machine for testing, by means of traction and pressure, the elasticity 



and density (solidity) of materials. 



The actual machine of the Imperial Institute was constructed by C. Faff in 

 Vienna. 



2. Testing machine for materials. Werder's system constructed for testing 



flexible elasticity and solidity. Executed by the Machine Factory 

 Company, Kell & Co., at Nuremberg. 



3. Testing machine for materials. Werder's system. Constructed for test- 



ing the elasticity of twisting and solidity. Executed by the Machine 

 Factory Company, Kless & Co., at Nuremberg. 



4. Machine and apparatus for ascertaining and determining the elasticity 



and solidity of wire, leather straps, thin ropes, &c. 



Executed in the former workshops of the Imperial and Royal Polytechnic 

 Institute. 



5. Optical apparatus for determining the modulus and the limits of elasticity 



by the application of tractive force, pressure, flexible elasticity, and 

 solidity. 



The original apparatus of the Imperial Polytechnic Institute were con- 

 structed by G. Starke and Kammerer, mechanicians, at Vienna. 



42 la. An Attraction Meter. An instrument for measuring 

 horizontal attraction. Dr. Siemens. 



This instrument consists of two horizontal tubes of wrought iron, ter- 

 minating at each end in a horizontal tube of cast iron. The first-named 

 horizontal tubes are partially closed at their extremities, and communicate 

 with the transverse tubes below their horizontal mid-section. The transverse 

 tubes communicate also by means of a horizontal glass tube of 2 millims. 

 diameter at a superior level to the former. 



The whole apparatus being mounted upon three set screws is filled to the 

 level of the half diameter of the transverse tubes with mercury, which mer- 

 cury also fills the whole of the longitudinal connecting tube ; the upper halves 

 of the cast-iron transverse tubes and the glass connecting tube are filled 

 with alcohol, comprising, however, a small bubble of air, which can be made 

 to occupy a central position in the glass tube by raising or lowering the set 

 screws. 



If a weighty object is approached to either extremity of the connecting 

 tube, an attractive influence will be exercised upon the mercury, tending to 

 a rise of level in the reservoir near at hand, at the expense of the more 

 distant reservoir ; and this disturbance of level between the two reservoirs 

 must exercise a corresponding effect upon the index of air in the horizontal 

 glass tube, moving it away from the source of attraction. The amount of 

 this movement must be proportional to the attractive force thus exercised. 

 Variations of temperature have no effect upon this instrument, because the 

 liquids contained on either side of the bubble of air are precisely the same 

 in amount ; and the total expansion of the liquids is compensated for by an 



