58 SEC. 3. MEASUREMENT. 



The sledge which carries the tracing work moves without greasing between 

 six finely polished carnelian plates ; by this arrangement any errors, which 

 might be caused by clotted grease, will be rendered absolutely impossible. 



297a. Micrometer Gauge and Screw, unfinished ; divisions 



adjusted to show -rs^r^ 11 f an incn - 



Maudslay Sons and Field. 



297b. Micrometer (Screw) Gauging Machine, by the late 

 Mr. Henry Maudslay, divided on the head of micrometer screw to 

 show Toro^th f an i nc k- 



Maudslay Sons and Field, Engineers, Lambeth. 



F. TIDE REGISTERS. 



255. A Registering Water-mark, of new construction, 

 which records the curve of the water-level and its mean height. 



Lieutenant- General Baeyer, President of the Geodetic 

 Institute at Berlin. 



678. Complete Magneto-electric Water-level Indica- 

 tor. Siemens and Halske, Telegraph Works, Berlin. 



279. Three Gauges, in enamel cast iron, for registering the 

 height of a river or lake. De Dietrich and Co., Niederbronn. 



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 posts are fixed by means of iron clamps to piers, vertical 

 embankments, &c., and serves for the observation of the stand of the water in 

 rivers, canals, lakes, and ponds. 



Placed properly distanced from one another into the chief water-courses 

 and its tributaries, it permits to observe the rise of the water, and consequently 

 thfe giving of timely warning, by telegraph or otherwise, to the inhabitants of 

 the districts concerned. 



280. Recording Tide Gauge, with self-acting calculation of 

 the mean height of the water (system, 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, constructed by Dennert and Pape of Altona, with 

 clock by T. Knoblich, of Hamburg, has a graphic apparatus for registering 

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

 automatically. The registration of the water-level is effected by means of 

 diamond points upon a cylinder placed horizontally for the accurate division 

 of the arc ; for the indication of the water-level a peculiar dividing machine 

 accompanies the flood-measurer. 



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 



