74 SEC. 3. MEASUREMENT. 



the radius of the discs C and E. The buoy then is fixed at a certain height 

 by a wire O. In this position the height of P. below a point given by 

 levelling is carefully measured. The absolute height of the water represented 

 by the chosen position of the buoy is now known. After this the mean 

 height corresponding to the same position (viz., the constant height of this 

 position) is calculated according to the result by a number of 10 or more 

 revolutions of the disc M. If the measured height corresponding to the 

 position of the buoy be equal h, and if the height given by the instrument 

 be equal m, h m is the absolute height (according to the levelling) from 

 which the mean height given by the instrument is taken. 



The diamond-point can then be fixed in a position to get a corresponding 

 diagram on the cylinder L to the absolute height given by levelling. 



F. H. EEITZ, 



Hamburgh, May 1876. . Civil Engineer in Hamburgh. 



281. Self-recording Tide-gauge, improved. 



H. C. Ahrbecker. 



In this instrument the whole of the paper can always be seen, and requires 

 renewal only once a month. The clock goes for 32 days. 



This instrument was designed to obviate the disadvantages which occur in 

 working the ordinary pattern. 



A float which rises and falls with the tide in an iron tube is attached to 

 one end of a chain that passes over a wheel, at the other end a counterpoise 

 hangs. When the float rises or falls it communicates its motion (by means 

 of the before-mentioned wheel) to a sliding pencil that moves across a strip 

 of paper drawn under it by the clock. 



In the model exhibited the distance between two lines across the paper, 

 = 2 hours, = 1 ft. in the length. 



This instrument can be made to work without any attention whatever for 

 12 months if necessary. 



282. Mareegraphe," or tide-gauge. Van Rysselberghe. 



G. MISCELLANEOUS LENGTH -MEASURING INSTRUMENTS. 



238. Measuring Wheel for determining distance by regis- 

 tering the number of revolutions ; the upper index pointing out 

 every single and the lower every 100 revolutions. 



Elliott Brothers. 



238a. Odometer or Way Measurer in gilt metal case 

 elaborately chased, an early example, probably made in the second 

 half of the 16th century. " Alexander Nesbitt. 



In Beckmann's History of Inventions there is a description of two instruments 

 resembling this, which belonged to the Emperor Rudolph II. (1576-1612). 



415b. Pare and Distance Indicator for Street Cabs. 



Robert Foster s Sunderland. 



This is an instrument for measuring the distance travelled by a cab or 

 other vehicle to which it may be attached. A driving band taking its motion 

 from the road wheel actuates counting wheels, and so pointers are made to 



