108 SEC. 3. MEASUREMENT. 



In this instrument a lever of the second order supports a glass cylinder 

 containing 100 grammes of mercury by means of a spiral spring attached to 

 its extremity. The variation of the weight of the mercury, due to a change 

 in the altitude of the point of observation, produces a corresponding variation 

 in the length of the spring ; this is rendered apparent by means of a pointer 

 30 centimeters in length, worked by a watch chain passing round a pulley on 

 the axis of the pointer and attached to the lever. 



42 le. Photograph of Pendulum of Altitude. 



A. Gerard, Liege. 



The pendulum consists of a glass rod mounted on knife edges ; the bob is 

 a cylinder of mercury attached to the glass rod by a spiral spring, thus 

 affording a perceptible variation in time of oscillation, due to variations of 

 gravity. 



42 5 a. Drawing of a Registering Statical Gauge for 

 Pressure in Guns. System of W. Paschkiewitsh. 



Captain W. Paschhiewitsh, St. Petersburg. 



2828. Dynamic Anemometer for obtaining the horizontal 

 and vertical pressure of air in motion, upon inclined surfaces of 

 different forms and angles. Manufactured by John Browning. 



The Council of the Aeronautical Society of Great Britain. 



This instrument is intended simultaneously to determine the component 

 parts i.e., how much pressure is due to the horizontal, and how much to 

 the vertical of a current of air when directed against planes of different 

 areas, and of different forms, at angles varying from 15 to 90. The experi- 

 ments are tabulated in the Aeronautical Society's Keport for the year 1871 

 (Hamilton and Co.). 



426a. Machine for measuring the slipping between hard 

 surfaces rolling in contact. Prof. Osborne Reynolds. 



This machine was constructed for the purpose of verifying the conclusions 

 of the exhibitor respecting rolling friction, and the existence of a certain 

 amount of slipping between two smooth surfaces of different curvature, or diffe- 

 rent hardness, when the one rolls on the other under pressure. It has also been 

 used to measure the slipping between the surfaces, when the one is driving 

 the other against various resistances and at various speeds, as well as the 

 wear of the surfaces. 



The large rolling surface is of cast-iron, supported so that it can rotate 

 freely, but otherwise rigidly fixed. For the smaller surface various materials 

 have been used, that exhibited being of steel ; this cylinder is supported so 

 that while its axis is always parallel to that of the larger cylinder, it can 

 be pressed against the latter with various degrees of pressure by means 

 of a lever acting through friction rollers. Arrangements are made for 

 recording the number of revolutions of both cylinders ; and connected with 

 "both spindles are driving pulleys and friction breaks on Appold's system, by 

 means of which the force to be transmitted can be regulated. 



An amount of slipping of not more than the one hundred thousandth part 

 of the distance rolled can be measured with this machine. 



The machine was constructed in Owen's College by Mr. Foster. 



