X. ANGLES. Ill 



435b. Dynamometer Waggon, for marking and registering 

 the tractive power, and the distances travelled. 



Eastern Railway of France Company, Paris. 



436. Theoretical Pressure Diagram for calculating the 

 mechanical work in a steam cylinder. 



H. Hadickc, Demmin, Pommerania. 



X. MEASUREMENT OF ANGLES. 



437. lO-inch Protractor, by Ramsden. Royal Society. 



438. Clinometer of Precision, employed in 1865 by Pro- 

 fessor Piazzi Smyth in the interior of the Great Pyramid. 



Prof. Piazzi Smyth. 



This instrument was made to order by T. Cooke and Sons, of York, in 1864, 

 at the cost of Andrew Coventry, Esq., of Edinburgh, for measuring the 

 interior slopes of the Great Pyramid. When thus used it was further 

 mounted on a deep wooden beam, 120 inches long, armed with feet of gun 

 metal. 



The angle measuring portion of the instrument is a complete circle, pro- 

 Tided with three pairs of opposite verniers, each reading to 10" in order to 

 eliminate errors of division as well as eccentricity, and the whole circle can 

 be moved and clamped on its centre so as to repeat any required angle all 

 round the circumference. On the voyage to Egypt a thermometer broke 

 inside the box, and the mercury tarnished the divided rim in parts. The 

 Pyramid angles thus obtained were printed in Vol. II. of " Life and Work 

 at the Great Pyramid," by Professor Piazzi Smyth, in 1867. 



439. Smaller Clinometer of Precision, with improved 

 mounting, readers, and level. Prof. Piazzi Smyth. 



This instrument was made to order by E. E. Sang, of Edinburgh, in 1869, 

 and intended for measuring Great Pyramid angles of slope. It carries its 

 own footbar, 25 inches long, has improved readers and illuminators, and a 

 chloroform level, as being more quick and frictionless than either ether or 

 alcohol. The circle can be rotated and clamped on its own centre for due repe- 

 tition of the angles round the circumference ; the verniers read to 1', and there 

 are supplementary verniers for investigating errors of division. 



435a. Method of ascertaining Angles of Torsion by means 

 of instruments constructed by Professor Wischnegradski. 



Laboratory of Mechanics, Technological Institute, St. 

 Petersburg. 



This is composed of a support fixed with two horizontal screws in the 

 given section of the beam subjected to torsion. This support carries a 

 horizontal axle, upon which is fixed an arc, bearing the teeth, whose pitch 

 measures an angle of 2,440 seconds. This arc gears with an endless screw, the 

 head of which bears a circle divided into 244 equal parts, and furnished 

 with a fixed decimal vernier ; the arc also carries a very sensitive level, placed 

 at the beginning of the experiment in a horizontal position. 



