200 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



raerous attempts by growing grass and trees on the sands 

 themselves, has gradually overwhelmed the villages it has 

 met in its course. The tidal observations made by the 

 survey in the Gulf of Kutch can only be satisfactorily car- 

 ried out by setting up the gauges on shore, over wells sunk 

 near the high-water line, and connected with the sea by iron 

 piping. The wells are twenty-two inches in diameter, and 

 the piping two inches, which dimensions do not materially 

 retard the tidal phenomena. 



GEODETIC SIGNALS USED IN THE ADIRONDACK SURVEY. 



In his interesting report on the survey of the Adirondack 

 wilderness of New York, Mr. Verplanck Colvin explains the 

 construction of a very simple signal which w T as used by him 

 with success to replace the expensive heliostat. This ar- 

 rangement was constructed of a vertical shaft, over which 

 Avas suspended by wires four square sheets of ordinary high- 

 ly polished tin, from which sheets respectively others were 

 suspended at various angles with the horizon. When the 

 sun was about rising or setting, the reflection from the sur- 

 face of the vertical sheets of tin were sufficient to make this, 

 signal visible at a distance of twenty miles, and that, too, in 

 every direction ; since by the action of the wind this arrange- 

 ment was kept constantly in rotation. Mirrors of glass were 

 at first tried, but were too easily broken in transportation, 

 while the sheets of tin were carried safely to all positions. 

 In the survey of so rough a country as the Adirondack re- 

 gion, the delicate and expensive instruments required in the 

 exact work of the Coast Survey could scarcely be employed, 

 except at an unjustifiably great expense. Mr. Colvin's sur- 

 vey looks to the rapid preparation of sufficiently accurate 

 maps of that region, based upon geodetic triangulation and 

 barometric determinations of the altitudes of prominent 

 points. 



THE SARANAC EXPLORING EXPEDITION. 



For the purpose of increasing the attractions of the ethno- 

 logical exhibition at the Centennial, undertaken by the Indian 

 Bureau and the Smithsonian Institution, the Secretary of the 

 Navy directed the United States steamer Saranac, bound on 

 a cruise to the North Pacific, to take on board at San Fran- 



