PHYSICS OF THE GLOBE. 117 



EQUALITY OF THE SURFACE LEVELS OF THE ATLANTIC 



AND PACIFIC OCEANS. 



Lines of levels run from sea to sea across the states of 

 Nicaragua and Panama, during the recent inter-oceanic ca- 

 nal surveys, made under the direction of Commander E. P. 

 Lull, U.S.N., confirm the fact that the surface levels of 

 the Atlantic and Pacific oceans at mean tide are exactly 

 the same. The Atlantic terminus of the Nicaragua line was 

 at San Juan del Norte, which is practically at the leeward- 

 most part of the Caribbean. The theory that the waters 

 of that sea are banked up by the northeast trade- winds, 

 forming a head for the Gulf Stream, seems thus to be dis- 

 proved. 



TIDAL CURRENTS IN THE GULF OF MAINE. 



A very interesting and valuable series of observations on 

 the Off-shore Tidal Currents in the Gulf of Maine, begun in 

 1877, have been completed during the present summer, un- 

 der the direction of Dr. C. P. Patterson, Superintendent Uni- 

 ted States Coast Survey, by Master Robert Piatt, U.S.N., 

 commanding the Coast Survey schooner Drift. These ob- 

 servations show that the tidal currents of this locality are 

 of sufficient strength to render their consideration in the 

 reckoning, especially of sailing-vessels, highly important; 

 and from them Professor Henry Mitchell, of the Coast Sur- 

 vey, has deduced rules and tables (part of which have already 

 been published, with a chart of the Gulf of Maine, showing 

 the positions of tide-stations and the localities of a number 

 of remarkable tide-rips. {Coast Survey JYbtice to Mariners, 

 No. 15, 1877.) It is found that on the line between Nan- 

 tucket Shoals and Cape Sable Bank (covered by the pub- 

 lished tables) the ebb-current runs southwardly during the 

 first four and a half hours, and the flood-current northward- 

 ly from the sixth to the eleventh hour after the moon's tran- 

 sit {northing or southing). Table I. gives for each of the lo- 

 calities named the times of turning from the flood-current 

 to the ebb, and of the reverse, with the direction and rate of 

 the flow all referred to the times of the moon's transit. Ta- 

 ble II. gives, for the same localities, the direction and rate of 

 the current for each hour after the time of high-water at Bos- 



