T 58 SE. 15. GEOGRAPHY. 



3035a. Capt. George's Improved Portable Artificial 

 Horizon. Made by H. Porter. Capt. C. George, E.N. 



This combines the reservoir for holding the mercury with the trough for 

 observation, the two being cast in one piece of iron, with a stopcock to let the 

 mercury run from the reservoir into the trough and back again when not in 

 use. This instrument has a perfectly worked parallel glass floating upon the 

 surface of the mercury, thus giving a perfectly brilliant surface and protected 

 from the action of the wind ruffling the surface of the mercury during ail 

 observation. This instrument combines the most perfect horizontal surface, 

 with exceeding portability (being less than one sixth the size of the ordinary 

 mercurial artificial horizon) and the greatest facility in use. 



3030a. Artificial Horizon, constructed by W. Herbst. 



M. W. Herbst, Pulkowa. 



M. Herbst's artificial horizon differs from that commonly used in the follow- 

 ing points : It is a box of rectangular shape, the mercury is enclosed in the 

 lower part of the box, and brought up on the silvered copper-plate by means 

 of a screw ; it admits of easy cleansing of the reflecting surface without any 

 loss of mercury ; its folding rectangular roof is covered with mica. 



303Ob. Plumb Level, or Artificial Horizon. 



Louis Brocher, Geneva. 



The instrument consists of a vertical rod, a horizontal disc, and a small 

 suspension chain. In operating, the instrument should be held suspended 

 . by. the chain, like a plumb-line, the eye being on a level with the disc ; the 

 projection of the plane of its upper and lower surface determines the 

 Horizon. As the rod is graduated, and as the distance from the eye to 

 the rod can be ascertained -by means of a line, the observer can determine ap- 

 proximately the sine of the angle "of elevation of the object building, tree, or 

 mountain and ascertain its height, if not absolutely, at all events relatively. 

 This instrument, which was originally invented with a view of supplying a 

 means (in sketching from nature) of ascertaining in any place the level of 

 the horizon (a matter indispensable for correct perspective), may be, and 

 has already been, useful to architects, engineers, geographers, tourists, and 

 also to agriculturists, for drainage purposes. Its small size renders it easy 

 to carry, and the rapidity with which observations can be taken enables them 

 to be repeated almost without intermission. 



3029. Mercurial Barometer, an instrument for travellers. 

 Made by H. Porter. Capt. C. George, R.N. 



Its peculiarity is, that the tube and cistern are carried empty, the mercury 

 being secured separately in an iron bottle. 



The cistern is used as a funnel. 



It is filled, when required, by the traveller, using the spiral cord, which is 

 kept in the tube while being filled. 



Circular motion is given to the spiral cord, which, acting on the dense body 

 of the mercury, forces the cord upwards, and out of the mercury, and with it 

 the air bubbles, leaving a superior vacuum, as shown by the mercury always 

 having a convex surface whether rising or falling. 



A spare tube is in same box. 



The instrument has been tested by E. H. Scott, F.R.S., Director of the 

 Meteorological Oflace, London, and also at the Kew Observatory, with good 

 results. It is now being used by travellers on the African lakes, and various 

 parts of the world. 



