252 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



of 300 miles, have been measured. Of the topographical sur- 

 vey 3700 square miles have been executed. The southern 

 section of the great Indian arc of the meridian has been com- 

 pletely revised, and Colonel Walker expresses his opinion 

 that no portion of the principal triangulation remains which 

 will ever be required to be revised, the last of the weak por- 

 tions having been made strong and comparable with the best 

 modern triangulation. In the course of the accurate work, 

 determinations have been made of the rate of progress of 

 certain sand hills near Cape Comorin. These travel pro- 

 gressively in a direction from west-northwest to east-south- 

 east, which is that of the prevailing winds in this locality. 

 They move at the rate of about seventeen yards per annum. 

 Tidal observations are being made in the gulf of Kutch which 

 promise to lead to valuable results. Very great difficulties 

 were found in selecting suitable stations for fixing the tide- 

 gauges difficulties that were overcome only by sinking 

 wells on the shore connected with the sea by open pipes, and 

 in which wells the tide-gauges were set up. 



THE HAEBOR OF NEW YORK. 



One of the most important recent contributions to the 

 Coast Survey has been the renewed investigation of all the 

 phenomena peculiar to New York Harbor, under the special 

 direction of Professor Henry Mitchell. The physical survey 

 of this harbor and its approaches require to be frequently 

 renewed, in order to keep track of the numerous changes 

 continually occurring both from natural and artificial causes. 

 In the recent report of Professor Mitchell to the Superintend- 

 ent of the Coast Survey, made in response to a resolution 

 of the New York Chamber of Commerce, it is shown that 

 the Jersey Flats no longer receive the deposits formerly car- 

 ried by currents upon its interior space. In consequence, 

 the deposits have accumulated to such an extent upon the 

 fore slope of the bank that the flats are rapidly growing out 

 into the main channel. If these flats are to be occupied by 

 buildings, provision should be made specially for keeping a 

 bold frontage. In the vicinity of Middle Ground Shoal and 

 of Gowanus a similar movement outward seems to be tak- 

 ing place from a similar cause. The importance of the East 

 River to the preservation of the entrance to New York Har- 



