616 SEC. 15. GEOGBAPHY. 



3029. The Mercurial Barometer, an Instrument for 

 Travellers. 



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



The mercury is 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 K. H. Scott, Esq., Director of the 

 Meteorological Office, London, and also at the Kew Observatory, Richmond, 

 with good results. It is now being used by travellers on the African lakes, 

 and various parts of the world. 



3030. Portable Artificial Horizon. 



Its improvement consists, not only in its reduced size and weight, but in its 

 mechanical arrangements, form, and moderate price. 



Secures altitudes near the horizon, as low as 3 ; saves time, and no waste 

 of mercury. 



Ibs. oz. in. in. 



Large size, weighs in the case - 4 10 measures 9 by 5 

 Small - 1 11 measures 6 by 3 



3O3Oa. 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. 



3O30b. 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 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 indis- 

 pensable 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. 



3031. The Double Pocket Sextant, an instrument for 

 travellers. 



