68 SEC. 3. MEASUREMENT. 



The first of these on the Niederbronn pattern is in black and white and 

 graduated to centimetres, the second on the Nancy pattern is graduated in 

 black and white for every two centimetres, and the third on the Paris pattern 

 is in blue and white graduated to five centimetres. 



These water-mark plates are fixed by means of iron clamps to piers, vertical 

 embankments, &c., and serve for the observation of the level of the water in 

 rivers, canals, lakes, and reservoirs. 



Placed at proper distances from one another in the chief water-courses and 

 its tributaries, they enable the rise of the water to be observed, and conse- 

 quently timely warning to be given, by telegraph or otherwise, to the inhabi- 

 tants of the districts concerned. 



28O. Recording Tide Gauge, with self-acting indications of 

 the mean height of the water (system of F. H. Reitz, Hamburg) ; 

 executed by Dennert and Pape, in Altona. 



Royal Prussian Geodetic Institute, Berlin. 



The tide-measuring system exhibited by the Royal Prussian Geodetic 

 Institution of the European measurement of a degree, at the instance of its 

 president, General Baeyer, and constructed by Dennert and Pape of Altona, 

 with clock by T. Knoblich, of Hamburg, has a graphic apparatus for regis- 

 tering the tide-curve and an arrangement by which the mean water-level is 

 indicated automatically. The registration of the water-level is effected bj r 

 means of diamond points upon a cylinder placed horizontally for the accurate 

 division of the arc. 



The mean water-level is indicated by means of two agate rollers with di- 

 visions, which slide upon a horizontal glass disc turned by the clock of the 

 tide-measurer, moved to and fro by the rising and falling water, and by the 

 rotation of the glass disc, and may be read off at any desired intervals of 

 time. 



The calculation otherwise necessary of the mean water-level (the true level 

 of the sea) from the indications of the registering apparatus is saved by the 

 above-mentioned mechanical arrangement, and effected automatically with 

 very great accuracy by the tide-measurer. 



The determination of the form and dimensions of the earth undertaken by 

 the European Committee for re-measuring degrees of longitude and latitude, 

 also contains the determination of the mean sea level at points on different 

 coasts, and its comparison by means of accurate levellings. During the last 

 few years the Committee has endeavoured, in consequence of these examina- 

 tions, to study the different apparatus and to promote a more exact observa- 

 tion of the tide corresponding to the exact levellings recently taken. 



These circumstances were the cause of a eommissiou from his Excellency 

 General Baeyer, President of the Central Office of the European Committee 

 for higher geodetic purposes, and the Royal Prussian Geodetic Institution, 

 to F. R. Reitz, instructing him to prepare a tide apparatus according to his 

 system. The instrument now exhibited was made by Dennert and Pape, of 

 Altona. and the clockwork by Theodor Knoblich, of Hamburgh. It is in- 

 tended by the Imperial German Admiralty to place this new instrument, 

 after the close of the Exhibition, on the Isle of Sylt, Schleswig. 



The commission given by his Excellency General Baeyer referred to the 

 construction cf a new instrument, combining a registering apparatus and 

 mechanical means of determining the mean level of the sea. The apparatus 

 here described is therefore a combination of both objects. 



A buoy A, moved up and down by the tide in a vertical shaft, turns a disc 

 C, about a horizontal axis, by means of a copper wire B. During the ebb 

 the wire B descends and turns the disc C; during the flood the same is 



